design criteria for sewage systems
Transcript of design criteria for sewage systems
Page 1Texas Commission on Environmental Quality Chapter 217/317 - Design Criteria For Sewerage System Rule Log No. 95100-317-WT
The Texas Commission on Environmental Quality (commission) proposes new Subchapter A,
§§217.1- 217.19; Subchapter B, 217.31-217.37; Subchapter C, 217.51-217.71; Subchapter D, 217.91
217.100; Subchapter E, 217.121-217.138; Subchapter F, 217.150-217.164; Subchapter G, 217.180
217.192; Subchapter H, 217.200-217.210; Subchapter J, 217.240-217.252; Subchapter K, 217.270
217.278; and Subchapter L, 217.290-217.307, concerning the design criteria for sewerage systems.
EXPLANATION OF PROPOSED RULE
The proposed rule package has three major goals: implementing the Commission’s goal of having all
water related rules under the 200 series by repealing Chapters 317 and 323 and incorporating its
provisions into new proposed Chapter 217; bringing the standards and criteria for wastewater treatment
systems up-to-date with current engineering practices and technology; and, updating the rules to better
reflect the current Commission’s permitting practices.
Chapter 317 was last comprehensively revised in 1986. Since then, minor revisions in 1988, 1990, and
1994, have addressed specific concerns, but have not sought to bring the rules in line with advances in
wastewater treatment technologies. Revisions are also needed to address requirements in other chapters
that are not referenced in Chapter 317, and to address requirements in current wastewater treatment
system discharge permits that are not addressed by current Chapter 317 requirements.
The proposed rule also includes the repeal of Chapter 323, which was last revised in 1978. This repeal
will incorporate provisions in Chapter 323 into Chapter 217 to bring the rule’s requirements in line with
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current advances in wastewater treatment technologies. Revisions are also needed to address
requirements in other chapters that are not referenced in Chapter 323, and to address requirements in
current wastewater treatment system discharge permits that are not addressed by current Chapter 323.
These new rules will ease the administrative burden on the commission by providing specific criteria by
which wastewater treatment systems must be built. These criteria must be used by licensed engineers in
designing the systems. Facility plans must be prepared by and have the seal of a licensed professional
engineer, ensuring that the system was designed in accordance with commission rules. The proposed rules
have been written to provide the engineering community with minimum standards for wastewater
treatment that the commission finds acceptable.
Variances
The rules as proposed will also provide some flexibility in allowing variances for innovative technology
that are approved on a case-by-case basis by the executive director. The objectives of these rules are
that wastewater treatment systems designed using these requirements will be a cost effective and
protective of human health and the environment. The proposed rules provide a mechanism for the
executive director to approve innovative technologies to treat domestic wastewater. Approvals of the
innovative technology may include the requirement for pilot studies, demonstration projects or
performance bonds. Performance bonds--to be used to pay for replacement of innovative technology
equipment or processes–may be required in some instances where a design engineer receives conditional
approval to use innovative technology and after a reasonable amount of time, the commission recognizes
that the technology does function correctly to meet the minimum design standards. The proposed rule also
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provides flexibility for the approval of nonconforming technology, that is, technology that is not addressed
in or conforms to the design criteria, but is known to perform or produce results that meet design criteria
standards. The rule also establishes criteria for a wastewater treatment facility and design criteria for
effluent re-use as authorized under 30 TAC Chapter 210.
Subchapter A
Proposed new §217.1, relating to Applicability, establishes that Chapter 217 applies to any individual who
proposes to construct facilities which will collect, transport, treat or dispose of domestic wastewater. The
chapter also provides the administrative processes governing implementation.
Proposed new §217.3, relating to Definitions, defines terms as used in this chapter. No definitions were
defined previously, except as otherwise noted in a subchapter.
Proposed new §217.4, relating to Purpose, clarifies that these design criteria are the minimum guidelines
which shall be used for the comprehensive consideration of domestic sewage collection, treatment or
disposal systems necessary to meet state water quality standards.
Proposed new §217.5, relating to Variances, clarifies current commission practices and procedures for
requesting a variance from the requirements of this chapter.
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Proposed new §217.6, relating to Relationship between Plans and Specifications Approval and
Wastewater discharge permits, clarifies that approved plans and specifications shall correspond to the
flow and effluent limitations set forth in the discharge permit. The rule also clarifies that approval of plans
and specifications does not relieve the facility of the responsibility to obtain a wastewater discharge
permit, nor does the approval of a wastewater discharge permit relieve the facility of the responsibility to
obtain approval of plans and specifications.
Proposed new §217.7, relating to Construction of Approved Facilities, establishes commission practices
and procedures that approval of plans and specifications alone does not imply that construction of the
facility may begin, until a wastewater discharge permit has been issued by the commission, as noted in
§26.027(c) of the Texas Water Code.
Proposed new §217.8, relating to Pre-existing Facilities, establishes commission practices and procedures
for determining the requirements for existing facilities approved prior to the effective date of these rules.
This section also specifies that these rules apply to modifications of existing facilities and to new facilities.
Proposed new §217.9, relating to Submittal Requirements, previously contained in §317.1(a), clarifies that
all proposed wastewater projects must submit a summary transmittal packet, and specifies the content and
process for submittal. This section also clarifies which plans need to be submitted for review by the
executive director and factors used to determine if a review is required.
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Proposed new §217.10, relating to Types of Approvals, previously contained in §317.1(a), clarifies the
type of approvals given plans and specifications and the conditions set with the specific approval. This
section also clarifies that approval of a facility does not relieve the owner or engineer of any
responsibilities. This section establishes criteria for approval of standard construction, as well as non
conforming and innovative technology. This section also establishes the requirements for approval of non
conforming or innovative technologies, including conditional approval with conditions, stipulations or
restrictions.
Proposed new §217.11, relating to Municipality Reviews, previously contained in §317.1(a), clarifies the
authority of municipalities to perform technical reviews of sanitary sewer collection systems within their
boundaries, and incorporates requirements of Texas Water Code 26.034(d) and (e).
Proposed new §217.12, relating to Change Orders, previously contained in §317.1(e), establishes
procedures for the submission of substantial design changes to a project after approval has been granted,
and clarifies commission policy relating to design changes.
Proposed new §217.13, relating to Completion Notification, previously contained in §317.1(e), establishes
the requirement that upon completion of construction, notice shall be provided to the executive director or
the review authority that the completed work substantially complies with this chapter. This also clarifies
commission policy relating to design changes.
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Proposed new §217.14, relating to Inspection, previously contained in §317.1(e), explains that at any time
during construction, any wastewater project is subject to inspection by the executive director or review
authority to determine compliance. This also clarifies commission policy relating to design changes.
Proposed new §217.15, relating to Operation and Maintenance Manual, previously contained in
§317.1(e), clarifies the requirement of developing an operations and maintenance (O&M) manual for any
proposed wastewater facility being constructed that promotes efficient and safe operations and
maintenance, monitoring, and reporting by the operators of the facility. This rule explains more thoroughly
commission requirements for O&M manuals.
Proposed new §217.16, relating to Cooperation Between Engineers and Operations Staff, previously
contained in 317.1(e), encourages discussions of the design elements between the engineers designing the
project and the staff that will be operating the system to maintain good engineering practices.
Proposed new §217.17, relating to Final Engineering Design Report, previously contained in §317.1(c),
clarifies the rule to establish the minimum requirements that should be included in a final engineering
design report.
Proposed new §217.18, relating to Final Construction Drawings and Technical Specifications, previously
contained in 317.1(d), clarifies the requirements for developing the final constructing drawings and
technical specifications for the project.
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Proposed new §217.19, relating to Compliance With Other Regulations, explains existing commission
policies and practices that the rules in this chapter do not supersede or replace any other state statutes or
local or federal requirements.
Subchapter B
Proposed new §217.31, relating to Applicability, explains that Subchapter B applies to all wastewater
treatment designs and details the design values which shall be utilized by the design engineer when
determining the sizes of wastewater treatment system components.
Proposed new §217.32, relating to Design of New Systems - Organic Loadings and Flows, explains the
organic loadings and flow values that must be used for new systems. This section clarifies and updates
commission practices and procedures, incorporates new procedures requested by the regulated
community, and adds new requirements in Chapter 319, relating to General Regulations Incorporated into
Permits.
Proposed new §217.33, relating to Design of Existing Systems - Organic Loadings and Flow, explains that
existing systems which are being modified or re-rated to meet new permit conditions may use historical
data as the design basis for justifying the sizing of existing or proposed wastewater treatment system
components. This section clarifies and updates commission practices and procedures, incorporates new
procedures requested by the regulated community, and adds new requirements in Chapter 319, relating to
General Regulations Incorporated into Permits.
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Proposed new §217.34, relating to One Hundred Year Flood Plain Requirements, previously contained in
§309.13, clarifies the requirement for showing 100-year flood plain limits on plans and the necessary
acceptable measures for locating a unit within the 100-year flood-plain, and incorporates requirements
relating to Federal Emergency Management Act Flood Plain Insurance Study.
Proposed new §217.35, relating to Backup Power Requirements, previously contained in §317.3(e),
clarifies the requirements for back-up power supply for system components.
Proposed new §217.36, relating to Buffer Zone and Design of Odor Abatement Facilities, explains that
construction of wastewater treatment facilities shall be done in accordance with the commission’s buffer
zone restrictions, contained in §309.13 (relating to Domestic Wastewater Effluent Limitations and Plant
Siting, Unsuitable Site Characteristics).
Proposed new §217.37, relating to Effluent Reuse, provides for the use of reclaimed water in place of
potable water whenever practical as designed by the engineer to encourage the recycling of effluent.
Proposed new §217.38, relating to Rating Systems, previously contained in §323.21
Proposed new §217.39, relating to Approved Ratings, previously contained in §323.22
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Proposed new §217.40, relating to Rating Procedures, previously contained in §323.23
Subchapter C
Proposed new §217.51, relating to Applicability, covers the design, construction, and testing standards that
are applicable to conventional sewer collection systems, as well as sewage lift stations, force mains and
reclaimed water conveyance systems.
Proposed new §217.52, relating to Edwards Aquifer, explains that collection systems built over the
Edwards Aquifer shall be designed in accordance with Chapter 213 of this title, relating to Edwards
Aquifer, in addition to the rules in this subchapter.
Proposed new §217.53, relating to Pipe Design, previously contained in §317.2(a), establishes the
requirements for all pipe designs, including but not limited to flow design basis and gravity pipe material.
This section clarifies requirements for separation distances between wastewater lines and water lines,
laterals and traps, odor/corrosion control, and structural analysis of flexible and rigid pipe. This section
incorporates provisions in Chapter 290 (relating to Public Drinking Water). Wastewater collection
facilities shall be designed to transport the peak dry weather flow from the service area. The choice of
sewer pipe shall be based on the type of waste conveyed. The materials used and methods to be applied
in making joints shall be included in the technical specifications. Separation distances between
wastewater lines and water lines, and between manholes and water lines, and other installation
requirements are specified. The horizontal distance between wastewater lines is specified. The vertical
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separation between wastewater lines and water lines, and other installation requirements are specified.
Requirements for laterals and taps are specified. Corrosive liners to reduce odor are described, with
requirements for the design report. Engineering specifications for systems located in active geological
faults are described. Capacity analysis and requirements are specified. Design requirements for the
sizing of new sewers are specified. Requirements for the structural analysis are specified. Engineering
requirements for flexible and rigid pipe are provided. The maximum and minimum slope for sewer
design is specified. Alignment of sewers is specified. Construction methods which utilize flexure of the
pipe joint are prohibited, and engineering requirements for horizontal pipe curvature are specified.
Maximum allowable manhole spacing is provided. Design requirements for inverted siphons and sag
pipes are specified. The requirements for bridged sections for pipes with restrained joints or monolithic
pipe are specified.
Proposed new §217.54, relating to Pipe Bedding, previously contained in §317.2(a)(5), establishes the
requirements for pipe bedding material, bedding compaction, envelope size and excavated trench width
and incorporates current industry standards for pipe bedding.
Proposed new §217.55, relating to Manholes and Related Structures, previously contained in
§317.2(c)(5), explains the placement, size, types and spacing of manholes, and increases manhole cover
size for worker safety. Manholes shall be placed at all points of change in alignment, grade or size of
sewer, with specific design requirements. Manholes shall consist of monolithic cast-in-place materials.
Spacing is specified for straight alignment and uniform grade, with modifications in areas subject to
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flooding. Inside diameters of manholes is specified, as well as size of manhole covers and design
requirements for manholes in the 100-year floodplain. Design specifications for manhole inverts are
provided. Manhole steps are prohibited. Design specifications are provided for connections for pipe to
manholes, venting and cleanouts.
Proposed new §217.56, relating to Rehabilitation/Maintenance of Collection Systems, explains that this
section does not apply to rehabilitation and maintenance projects and that these activities must be done in
accordance with local authority guidelines.
Proposed new §217.57, relating to Trenchless Design for Collection Systems, explains that pipe
installations using trenchless design shall be considered nonconforming technology and shall be subject to
review and approval of the reviewing authority prior to construction.
Proposed new §217.58, relating to Testing Requirements for Installed Gravity Collection Lines, previously
contained in §317.2(a)(4), establishes the criteria for infiltration, exfiltration, or low-pressure air tests for
gravity collection lines. Low pressure air tests are described for pipes based on size of pipe, utilizing
pressure loss or leakage within specified times. Criteria for infiltration and exfiltration tests are described
based on hydrostatic head test per 24 hours. Specific requirements for construction within the 25-year
floodplain are described. Deflection testing is required for all flexible pipe, with specific testing
requirements based on size of pipe. This section incorporates current engineering practices for the sizing
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of rigid mandrel. Design requirements and construction of the rigid mandrel are described. Adjustable or
flexible mandrels are prohibited.
Proposed new §217.59, relating to Testing Requirements for Manholes, previously contained in
§317.2(c)(5), explains that manholes shall be tested for leakage separately and independently of the
wastewater lines by hydrostatic exfiltration testing, vacuum testing or other methods acceptable to the
Executive Director or the designated Review Authority. Maximum leakage for hydrostatic testing is
specified. Alternative test methods and hydrostatic exfiltration tests are described. The option of vacuum
testing was added and requirements for vacuum testing are specified.
Proposed new §217.60, relating to Lift Station Site Selection, previously contained in §317.3(a),
establishes the criteria for selecting lift station sites. Specific site access, security, flood protection and
odor control are specified.
Proposed new §217.61, relating to Lift Station Wet Well/Dry Well Design Considerations, previously
contained in §317.3(b), establishes criteria for pump controls, flood protection, wet wells, lift station
ventilation and dry well sump pumps. This section also proposes a new equation for calculating minimum
wetwell volume. Lift station pump controls are described, electrical equipment shall be protected during a
100-year flood event, design criteria for wet wells and dry wells are specified. Dry well access is
specified. Design criteria for lift station ventilation are specified, including passive ventilation for wet
wells, and mechanical ventilation in lift stations. Design criteria for both wet wells and dry wells are
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provided for mechanical ventilation. Wet well slopes are specified. Requirements for hoisting equipment
are described, as well as dry well valve vault drains and dry well sump pumps. Design criteria for sump
pumps are provided, including pump capacity and piping.
Proposed new §217.62, relating to Pumps for Lift Stations, previously contained in §317.3(c), establishes
general requirements for the pumps that may be used in the design of lift stations. the rule was
reorganized and updated to incorporate current engineering practices. General design criteria for pumps
are provided. Lift station requirements including pumping capacity, pump head calculations and flow
control are provided. Design criteria for self-priming pumps and vacuum priming pumps are provided.
Vertical positioning of pumps is specified. Design of grinder pumps is specified.
Proposed new §217.63, relating to Lift Station Piping, previously contained in §317.3(d), establishes
requirements for pump suctions, valves and piping that shall be used in the design of lift stations. Design
criteria for horizontal pump suctions are specified. Requirements for check valves and piping are
specified.
Proposed new §217.64, relating to Emergency Provisions for Lift Stations, previously contained in
§317.3(e), establishes the provisions, such as retention capacity, reliability of portable generators, and spill
containment structures for emergency situations should a lift station fail. The rule was reorganized and
updated to incorporate current engineering practices. Lift stations shall be designed to prevent stream
pollution in the event of an overflow or surcharge of raw sewage. Alarm systems and service reliability
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are required for lift stations. Retention capacity design criteria are specified. Emergency electrical
power using dual-fed electrical power is described. On-site generators may be used as emergency
power. Design criteria for portable generators or pumps are specified. Spill containment structures may
be used in addition to one of the service reliability options with specified requirements.
Proposed new §217.65, relating to Materials For Force Main Piping, previously contained in §317.2(d),
was reorganized and establishes that force main piping material shall be designed to withstand all working
pressures, plus surge stresses generated by instantaneous pump stoppage due to power failure.
Proposed new §217.66, relating to Force Main Joints, incorporates current engineering practices for joints
of force mains in buried service. Joints shall be either push-on rubber gaskets or mechanical joints with a
pressure rating equal to or greater than the force main pipe material.
Proposed new §217.67, relating to Force Main Pipe Bedding, explains that bedding for force mains shall
comply with §217.54 of this title (relating to Pipe Bedding).
Proposed new §217.68, relating to Identification of Force Main Piping, incorporates safety requirements
that detector tape, on which is printed in a minimum of 1½ inch tall letters the words "pressurized
wastewater" continuously along the tape, shall be laid in the same trench, above and parallel to the force
main.
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Proposed new §217.69, relating to Force Main Design, previously contained in §317.2(d), clarifies and
updates the requirements for velocities, detention time, water hammer from surges, gravity main
connection, vertical alignment, pipe separation, odor control and air release valves for force main design.
Proposed new §217.70, relating to Force Main Testing, incorporates portions of previous §317.2(d)(4),
and explains the required pressure testing procedures for force mains.
Proposed new §217.71, relating to Reclaimed Water and Irrigation Facilities, incorporates provisions in
Chapter 210 (relating to Use of Reclaimed Water), explains the requirements for the design of distribution
systems that will convey reclaimed water to a user. Designs shall be reviewed and approved by the
executive director. Design criteria for gravity piping are specified, including testing requirements, flow
velocities, solid deposition, appurtenances identification and cross-connection controls. Site selection
criteria are specified. Design criteria for reclaimed water pump stations are provided, including pump
controls, pumps and lift station valving. Design criteria for force main piping are provided, including color
identification and isolation valve specifications..
Subchapter D
Proposed new §217.91, relating to Applicability, establishes that Subchapter D is applicable to the design
criteria for alternative sewer collection systems. Design criteria for component sizing are provided.
Design criteria for both on-site and off-site components are specified.
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Proposed new §217.92, relating to Design of Alternative Collection Systems - Component Sizing,
previously contained in §317.2(d), updates current engineering practices and establishes that components
shall be sized based on existing flow data from similar types of systems and service areas, whenever such
data is available.
Proposed new §217.93, relating to Gravity Lines, Force Mains and Lift Stations in Alternative Collection
Systems, §317.2(d), clarifies existing regulations for discharge into alternative systems. The rule explains
that, except where specifically modified in this subchapter, designs for alternative sewer collection
systems shall comply with the applicable requirements of subchapter C in addition to the requirements of
this subchapter. The engineer shall provide an operations and maintenance manual. Requirements for the
manual are specified. Requirements for the holder of the wastewater permit are described.
Management of the alternative collection system may be wither private or public service provider.
Grinder pumps and effluent pumps are not required.
Proposed new §217.94, relating to Management, previously contained in §317.2(d), clarifies the
management structure for alternative wastewater collection systems. The rule explains that due to
alternative wastewater collection systems being constructed of mechanical parts and equipment, a staffing
management structure shall be established to insure that requirements for the operation and maintenance
of the system are maintained. Requirements of the sewer service agreement are specified.
Requirements for existing alternative sewer system components are specified. The manager/operator of
the collection system shall have final approval for materials and equipment. The manager/operator shall
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also inspect and approve installation of the collection system, shall be granted access for inspection at all
reasonable times, and shall have the right to make emergency repairs. The service agreement shall
delineate costs.
Proposed new §217.95, relating to Sewer Service Agreements, previously contained in §317.2(d),
clarifies current agency practice for sewer service agreements and establishes that a sewer service
agreement shall be executed between the manager/operator of the alternative wastewater collection
system and the property owner that allows for the placement and maintenance of alternative system
components located on private property, and lists the times for which the manager/operator shall be
responsible. This section also specifies provisions which must be included in the sewer service
agreement.
Proposed new §217.96, relating to Design of Small Diameter Effluent Sewers (SDES), previously
contained in §317.2(d), clarifies and establishes the criteria for components of a Small Diameter Effluent
Sewer, including interceptor tank design, pre-treatment units, service line design and collection system
design.
Proposed new §217.97, relating to Design of Pressure Sewers, previously contained in §317.2(d),
clarifies the requirements for pressure sewer systems, including grinder pump sewer systems and septic
tank effluent pump systems. Design criteria include service line requirements, on-site pressure sewer
system mechanical equipment requirements, discharge piping requirements, and collection system design.
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Proposed new §217.98, relating to Vacuum Sewer Systems, previously contained in §317.2(d),
establishes the design requirements for vacuum sewers which are non-conforming technology.
Proposed new §217.99, relating to Testing Requirements for Alternative Sewer Collection Systems,
establishes testing methods and requirements for all components of alternative wastewater collection
systems.
Proposed new §217.100, relating to Termination Facilities for Alternative Sewer Collection Facilities,
describes the requirements for the termination of an alternative wastewater collection system at treatment
facilities or into an existing conventional sewer, that are in close proximity to human habitation.
Wastewater collection systems shall be designed to minimize the potential for odors.
Subchapter E
Proposed new §217.121, relating to Applicability, establishes that Subchapter E applies to preliminary and
primary treatment systems used at wastewater treatment systems.
Proposed new §217.122, relating to Coarse Screening Devices, previously contained in §317.4(b),
explains which systems require the installation of a coarse screening device, such as a bar screen.
Proposed new §217.123, relating to Coarse Screening Devices - Redundancy Requirements, previously
contained in §317.4(b), more thoroughly and specifically explains the requirement of providing bypass
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channels, sized to handle the two-hour peak flow of the facility, to bypass flow around any coarse
screening device.
Proposed new §217.124, relating to Design of Coarse Screening Devices, incorporates new safety
requirements and the design requirements for coarse screening devices located in an enclosed area, such
as location, screen openings, hydraulics and corrosion resistance of coarse screening devices.
Proposed new §217.125, relating to Coarse Screening Devices - Screenings and Debris Handling,
previously contained in §317.4(b), explains new requirements that facilities shall be provided for the
storage of a minimum of one-day of screenings and debris. This section also provides requirements for
screenings and debris handling including container covers, runoff control, drainage and disposal of debris.
Proposed new §217.126, relating to Fine Screens, previously contained in §317.4(b), explains that
although not required, fine screens may be used in lieu of coarse screening devices.
Proposed new §217.127, relating to Fine Screens - BOD5 Removal, previously contained in §317.4(b),
clarifies and explains that fine screens shall not be considered equivalent to primary sedimentation for the
removal of BOD5. Engineering design requirements for the use of fine screens are provided.
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Proposed new §217.128, relating to Fine Screens - Redundancy Requirements, previously contained in
§317.4(b), explains that where BOD5 reduction is credited through the fine screen, dual fine screen
treatment trains shall be provided.
Proposed new §217.129, relating to Fine Screen Design Parameters, sets the design parameters if fine
screens are to be installed according to manufacturer’s recommendations for removal of oil and grease,
cleaning devices, automatic conveyance of materials, and construction details.
Proposed new §217.130, relating to Fine Screens - Screenings and Debris Handling, previously contained
in §317.4(b) clarifies the management and disposal of screenings and debris from fine screens shall be
managed and disposed of in accordance with §217.125 of this title (relating to Coarse Screening Devices
- Screenings and Debris Handling).
Proposed new §217.131, relating to Grit Removal Facilities establishes that grit removal facilities capable
of removing inert biodegradable particles larger than 0.2 mm in size are required for all wastewater
treatment systems for proper operation of anaerobic digesters.
Proposed new §217.132, relating to Grit Removal Chambers - Redundancy Requirements, previously
contained in §317.4(b), explains that dual grit removal processes shall be provided whenever grit removal
is required.
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Proposed new §217.133, relating to Design Requirements for Various Types of Grit Chambers, previously
contained in §317.4(b), establishes updated and adds new design criteria for horizontal flow grit
chambers, aerated grit chambers, mechanical grit chambers, cyclonic degritters, and vortex chambers.
Proposed new §217.134, relating to Grit Handling, previously contained in §317.4(b), explains the
requirements for grit washing, drainage for grit washing facilities and grit storage areas, grit chambers and
grit storage.
Proposed new §217.135, relating to Preaeration Facilities, previously contained in §317.4(b), provides
flexibility for preaeration facilities in sizing and design based on the use of preaeration.
Proposed new §217.136, relating to Flow Measurement, previously contained in §317.4(b), provides the
requirement that all wastewater treatment facilities have a means of accurate effluent flow measurement.
Also provides the requirements for primary, including weirs and flumes, and secondary measuring
devices.
Proposed new §217.137, relating to Flow Equalization Basins, previously contained in §317.4(b), explains
new design requirements for the use of flow equalization basins, and the mixing, aeration, volume and
pumped flow requirements of equalization basins.
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Proposed new §217.138, relating to Primary Clarifiers - Design Basis, previously contained in §317.4(d)
establishes the design criteria for primary clarifiers, including the requirements for inlets, scum removal,
effluent weirs, basin sizing, sidewater depth, freeboard, drains, operator protection, primary clarifiers for
BOD5 removal and primary clarifiers for sludge pumping and piping.
Subchapter F
Proposed new §217.150, relating to Applicability, explains that Subchapter F provides the design
requirements for activated sludge systems and is applicable to these systems.
Proposed new §217.151, relating to General Requirements for Activated Sludge Aeration Basins,
previously contained in §317.4(g) provides the requirements for minimum dissolved oxygen concentration
in aeration basins and alternate aeration volume. The rule also adds new prohibitions of contact
stabilization systems for nitrification to ensure compliance with permit requirements under Chapter 305
(relating to Consolidated Permits).
Proposed new §217.152, relating to General Requirements for Activated Sludge Clarifiers, previously
contained in §317.4(d), provides the requirements for activated sludge clarifier components such as inlets,
scum removal, effluent weirs, sludge lines, sludge collection equipment, pumped inflow, and side water
depth. This section also provides restrictions on hopper bottom clarifiers, prevents short circuiting of
influent and effluent weirs, and specifies the calculations which are required to determine return sludge
pumping capacity.
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Proposed new §217.153, relating to General Requirements Which Apply to both Aeration Basins and
Clarifiers, previously contained in §317.4(d) and (g), establishes requirements such as construction
material, freeboard, and flow splitting that pertain to both aeration basins and clarifiers. The rule also
adds new design requirements for flow splitting to maximize facility operations during emergency repairs.
Proposed new §217.154, relating to Aeration Basin and Clarifier Sizing - Traditional Design Approach,
previously contained in §317.4(d) and (g) provides the standard design values which shall be used to size
aeration basins and clarifiers when using traditional design approaches.
Proposed new §217.155, relating to Aeration Basin and Clarifier Sizing - Volume-Flux Design Approach,
provides new designs integrating advanced technology for the sizing of aeration basins and clarifiers when
using the volume-flux design method as an alternative to the traditional design method.
Proposed new §217.156, relating to Aeration Equipment Sizing, previously contained in §317.4(g),
updates and explains the methods for achieving the proper oxygen requirements of the wastewater by
mechanical or diffused aeration systems.
Proposed new §217.157, relating to Sequencing Batch Reactors (SBR), explains the requirements for the
new design criteria for technological advances requirements in using SBRs, including the number of
basins/tanks, aeration requirements, utilization of duplicate controllers, measures for flow variation and
decanting devices.
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Proposed new §217.158, relating to Solids Management, previously contained in §317.4(d) and §317.5(a),
more thoroughly and specifically provides the requirements for properly handling sludge within the
wastewater system, including solids recycling and monitoring, solids wasting and solids blanket, return
activated sludge pump design, waste activated sludge pump design and piping.
Proposed new §217.159, relating to Process Control, previously contained in §317.5(a), provides the
criteria for implementing solids retention time control and aeration system control.
Proposed new §217.160, relating to Operability and Maintenance Considerations, previously contained in
§317.5(a), clarifies and explains more thoroughly and specifically, the requirements of having equipment
operate at the temperature extremes of the plant location and having equipment housed in facilities with
adequate room for removal, repair and installation of equipment.
Proposed new §217.161, relating to Electrical and Instrumentation Systems, previously contained in
§317.7, explains electrical power supply requirements for plant equipment and establishes safety
requirements for protection of equipment.
Proposed new §217.162, relating to Flow Measurement, previously contained in §317.4, establishes new
requirements for adding process control measurements for plants with a design flow greater than 400,000
gallons per day.
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Proposed new §217.163, relating to Advanced Nutrient Removal, previously contained in §317.4(h), adds
more flexibility for advanced nutrient removal which shall be considered innovative and/or nonconforming
technology and will be subject to the requirements of §217.10(b) (relating to Types of Approvals) of this
title.
Proposed new §217.164, relating to Appendix I, Volume-Flux Design Approach, provides new
requirements for alternative volume-flux design approach, aeration basin sizing, and clarifier sizing.
Subchapter G
Proposed new §217.180, relating to Applicability, provides the requirements in Subchapter G for trickling
filters, rotating biological contactors, submerged biological contactors and filtration systems.
Proposed new §217.181, relating to Trickling Filters - General Requirements, previously contained in
§317.4(e), clarifies the general requirements for the use of trickling filters which are secondary aerobic
biological processes used for treatment of sewage. This section also provides requirements for
determining process applicability and pretreatment.
Proposed new §217.182, relating to Nitrifying Trickling Filters - Additional Requirements, provides new
requirements for using trickling filters to provide nitrification sufficient to meet the new requirements of a
discharge permit, including ventilation, temperature, pH, predation, hydraulic application rates, media,
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tertiary nitrificaton filter, and combined BOD/nitrification filters and to update the rules to comply with
engineering design advances.
Proposed new §217.183, relating to Dual Treatment Systems Utilizing Trickling Filters, explains new
requirements and processes for use of trickling filters or other attached growth units in series with
suspended growth processes to update the rules to comply with engineering design advances. This
section includes classification of dual treatment processes, design criteria for attached and suspended
growth processes, and treatment unit design criteria.
Proposed new §217.184, relating to Rotating Biological Contactors (RBC) - General Requirements,
previously contained in §317.4(f), provides the requirements and provisions for the use of improved
rotating biological contactors (RBC) units, including pretreatment, enclosures and ventilation, media
design, design flexibility, tank configuration, control of unwanted growth in the initial stages, downtime
maintenance provisions, bearing maintenance, organic loading design requirements, hydraulic loading
design requirements, stages of RBC units, drive systems, and dissolved oxygen to update the rules to
comply with engineering design advances.
Proposed new §217.185, relating to Nitrifying Rotating Biological Contactors (RBC) - Additional
Requirements, previously contained in §317.4(g), provides additional requirements for RBCs used for
BOD5 removal and nitrification of domestic wastewater.
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Proposed new §217.186, relating to Dual Treatment Systems Utilizing Rotating Biological Contactors
(RBC), explains the new requirements for allowing RBC units to be used in conjunction with other
systems to take advantage of the strengths of both systems and to update the rules to comply with
engineering design advances.
Proposed new §217.187, relating to Submerged Biological Contactors (SBC) - General Requirements,
explains the new process for designing submerged biological contactors (SBC) under the same criteria as
RBCs except that two air headers will be required for each SBC unit, and any submerged bearings shall
be sealed to update the rules to comply with engineering design advances.
Proposed new §217.188, relating to Dual Treatment Systems Utilizing Submerged Biological Contactors
(SBC), explains the new process for designing SBC units to be used in conjunction with other systems to
take advantage of the strengths of both systems as long as the design engineer submits information
describing how the proposed system will provide the required treatment levels.
Proposed new §217.189, relating to Filtration - General Requirements, previously contained in §317.4(l),
updates and clarifies the general requirements for filtration systems such as permit water quality
requirements, water quality requirements, redundancy, source of backwash water, disposition of
backwash water, place in sequence of treatment units, overload conditions and control of slime growth.
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Proposed new §217.190, relating to Additional Specific Design Requirements for Deep Bed, Intermittently
Backwashed, Granular Media Filters, previously contained in §317.4(l), updates and clarifies additional
design criteria for deep bed, intermittently backwashed, granular media filters including application rates,
media design, backwash system, underdrain system, tank design and controls.
Proposed new §217.191, relating to Additional Specific Design Requirements for Multi-Compartmented,
Low Head, Automatically Backwashed Filters, previously contained in §317.4(l), updates and clarifies
additional design criteria for multi-compartmented, low head, automatic backwash filters including
application rates, media design, backwash system and traveling bridge.
Proposed new §217.192, relating to Alternative Designs for Effluent Polishing, explains that the use of
other processes for tertiary suspended solids removal, such as microscreens or countercurrent, continuous
filtrate and backwash flow filters, will be considered nonconforming technologies and shall be subject to
the requirements of §217.10(b) of this title (relating to Approvals of Innovative and Nonconforming
Technologies.)
Subchapter H
Proposed new §217.200, relating to Applicability, explains that Subchapter H applies to the minimum
design requirements for Imhoff tanks, constructed wetlands, facultative ponds, aerated and partially-
aerated ponds, stabilization ponds, treated effluent storage ponds, evaporative pond systems and overland
flow processes.
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Proposed new §217.201, relating to Primary and Secondary Treatment Units, previously contained in
§317.4, clarifies commission policy on the requirements for primary and secondary treatment units as they
pertain to this chapter.
Proposed new §217.202, relating to General Design Considerations for Natural Systems, previously
contained in §317.4 and §317.15, updates requirements which apply to one or more of the natural
systems covered by this subchapter including specific references to the natural treatment systems or units
for which the design criteria in the subsection apply. Natural systems include flow distribution,
windbreaks and screening, maximum liner permeability, embankment design and construction, disinfection,
sampling point significance, and storm water drainage.
Proposed new §217.203, relating to Imhoff Tanks, provides new updated design criteria which shall be
utilized when constructing Imhoff tanks including settling compartment, surface loading, scum baffles, gas
vents, digestion compartment loading, Imhoff tank dimensions, sludge removal, odor management,
treatment efficiency, and material and construction.
Proposed new §217.204, relating to Facultative Ponds, previously contained in §317.4, provides the
design criteria for facultative ponds, including configuration of inlets and outlets, depth, organic loading,
odor control, and removal efficiency.
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Proposed new §217.205, relating to Aerated Ponds, previously contained in §317.4, provides updated
requirements for complete mix aerated ponds, which are those which have adequate mixing to maintain all
biological solids in suspension and provide uniform oxygen concentrations in the pond. This section also
provides requirements for partially mixed aerated ponds which allow for settling and anaerobic
composition of a portion of the influent suspended solids as well as the biological solids generated in the
system.
Proposed new §217.206, relating to Wastewater Stabilization Ponds, previously contained in §317.4,
provides the requirements for ponds which are designed as secondary treatment units to treat suspended
and dissolved organic matter in wastewater, including odor management, number of wastewater
stabilization ponds, pond dimensions and water level considerations, hydraulic and piping considerations,
maximum organic loading on stabilization ponds, and inlet and outlet structures.
Proposed new §217.207, relating to Evaporative Ponds, previously contained in §317.4, establishes
existing commission practices for general requirements for the use of evaporative ponds, including size
and number, odor management, liners, and configuration of depth and loading, embankment, and inlet and
outlet structures of the pond.
Proposed new §217.208, relating to Constructed Wetlands, previously contained in §317.15, updates and
clarifies the general requirements for these artificially constructed complexes of saturated substrates,
emergent and submergent vegetation, animal life, and water designed to simulate natural wetland ecologic
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conditions based on advances in engineering design. This section includes general design considerations,
free water surface systems, and subsurface flow systems.
Proposed new §217.209, relating to Overland Flow Process, previously contained in §317.40, updates and
clarifies the requirements for the use of the overland flow process (O.F.) as a treatment of wastewater
including nitrification, design constraints, hydraulic loading rate, climate for wastewater storage, storage
basin design, storage basin construction, nuisance odor prevention, soil testing, distribution systems,
terraces, vegetation selection, buffer zone and sampling.
Proposed new §217.210, relating to Integrated Facultative Ponds, explains new engineering design for
integrated facultative ponds which shall be considered nonconforming technology. The section provides
design criteria for integrated facultative ponds including configuration of inlets and outlets, depth, organic
loading, odor control, and removal efficiency.
Subchapter J
Proposed new §217.240, relating to Applicability, explains that Subchapter J applies to the minimum
design requirements for sewage sludge treatment processes and treatment units including thickening,
stabilization, and dewatering.
Proposed new §217.241, relating to Control of Sludge and Supernatant Volumes, previously contained in
§317.5(a)(2), establishes that wastewater treatment facilities shall provide for the return of supernatant, or
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centrate, resulting from sludge processing activities to the head of the treatment works, discharged at a
point preceding the aeration system, or preceding the secondary treatment units if no aeration exists at the
plant.
Proposed new §217.242, relating to Sludge Piping, previously contained in §317.5(a)(3), provides
requirements for piping used in the treatment of sludge, including verifying that any sludge piping included
as part of the sludge processing facilities has sufficient gradient to insure the flow of sludge.
Proposed new §217.243, relating to Sludge Pumps, previously contained in §317.5(a), explains the
requirements for the design of sludge transfer pumps, with design based on both the quantity and
character of the anticipated solids load to be handled by the pumps.
Proposed new §217.244, relating to Exclusion of Grit and Grease from Sludge Treatment Units,
incorporates agency practices contained in provisions of Chapter 312 of this title (relating to Sludge Use,
Proposal, and Transportation) and explains the requirement that the design of the wastewater facility shall
minimize to the greatest extent deemed possible by the design engineer, the discharge of grit, debris, oil or
grease to the sewage sludge treatment units.
Proposed new §217.245, relating to Ventilation, provides new safety requirements that any sludge
treatment or processing areas, where the presence of fumes or gases of a level sufficient to constitute a
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public health hazard or a threat to air quality, shall be provided with sufficient ventilation to eliminate these
dangers.
Proposed new §217.246, relating to Odor Control, explains that the engineer shall design all sewage
sludge process units to minimize or eliminate nuisance odors.
Proposed new §217.247, relating to Chemical Pretreatment of Residuals, establishes criteria
incorporating new state and federal requirements in 40 CFR 503 and Texas Health and Safety Code,
Chapter 361, for the use and handling of chemicals and equipment that can be added to enhance solids
removal, necessary for many sludge treatment or processing units. This section includes chemical
selection, safety provisions for storage of chemicals, minimum chemical supply, chemical handling,
housing of chemicals, feed equipment, solution tanks, and requirements for chemical application.
Proposed new §217.248, relating to Sludge Thickening, establishes minimum criteria for sludge thickening
for use in volume reduction and conditioning of sludge prior to sludge treatment. The section establishes
commission practices including general requirements for thickeners, specific requirements for mechanical
(gravity) thickeners, specific requirements for dissolved air flotation thickeners, and specific requirements
for centrifugal thickeners.
Proposed new §217.249, relating to Sludge Stabilization, previously contained in §317.5, updates new
design requirements incorporating new state and federal requirements in 40 CFR 503 and Texas Health
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and Safety Code, Chapter 361, for the stabilization processes including anaerobic digestion, aerobic sludge
digestion, heat stabilization, and alkaline addition.
Proposed new §217.250, relating to Sludge Dewatering, updates and clarifies previous §317.5(e) and
incorporates new minimum design criteria for comprehensive consideration of sewage sludge dewatering
unit processes, including general requirements, sludge conditioning, sludge drying beds, modified drying
beds, rotary vacuum filtration, centrifugal dewatering, plate and frame presses, and belt presses.
Proposed new §217.251, relating to Sludge Storage, specifies new criteria for the storage of residuals
after processing and prior to final disposal or removal from the site, including general criteria, solids
storage, dewatered solids storage, and dried solids storage to protect water quality.
Proposed new §217.252, relating to Final Use or Disposal of Sludge, explains the new design criteria and
requirement that the engineer shall include the final use or disposal of sewage sludge in the design of the
wastewater treatment facility, including quantities of solids, pollutants, pathogens, vector attraction,
emergency provisions and weather factors. ???40 CFR 503 and H&SC
Subchapter K
Proposed new §217.270, relating to Applicability, explains that Subchapter K applies to the requirements
for disinfection, dechlorination, post aeration, and sampling point locations.
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Proposed new §217.271, relating to Chlorine and Sulfur Dioxide Disinfection and Dechlorination Systems,
previously contained in §317.6, incorporates the requirements for chlorine, sulfur dioxide disinfection, and
dechlorination systems, including redundancy, capacity and sizing, dosage control, handling of chemicals,
and equipment and materials. The section also adds new dechlorination requirements under Chapter 307
(relating to Surface Water Quality Standards) and Texas Water Code, §26.023.
Proposed new §217.272, relating to Design of Sodium Hypochlorite and Sodium Bisulfite Systems,
incorporates new design criteria and specifies general requirements for sodium hypochlorite and sodium
bisulfite systems including capacity and sizing, dosage control, handling of chemicals, equipment and
materials, and safety.
Proposed new §217.273, relating to Application of Disinfection and Dechlorination Chemicals, previously
contained in §317.6, explains the criteria for chlorine mixing requirements and disinfection contact basins
and adds new dechlorination contact time based on new water quality standards under Chapter 307
(relating to Surface Water Quality Standards) and Texas Water Code, §26.023.
Proposed new §217.274, relating to Other Chemical Disinfection and Dechlorination Systems, explains
that all other chemical disinfection or dechlorination systems such as chlorine dioxide, ozone, all tablet or
powder disinfection and dechlorination systems, and liquid solution disinfection and dechlorination systems
other than sodium hypochlorite and sodium bisulfite shall be subject to the requirements of §217.10(b) of
this title (relating to Innovative and Nonconforming Technologies).
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Proposed new §217.275, relating to Ultraviolet Light Disinfection Systems, updates previous §317.6 to
incorporate new design criteria and explains the permit requirements including redundancy, monitoring and
alarms, hydraulics, dosage and system sizing, reactor design and safety, for the use of ultraviolet (UV)
disinfection systems.
Proposed new §217.276, relating to Power Reliability, previously contained in §317.3, explains the safety
requirement that all disinfection systems shall include backup power provisions which are capable of
providing sufficient power to operate all power dependant components of the disinfection system during
any power outage.
Proposed new §217.277, relating to Post Aeration, explains that post aeration shall be provided as needed
to ensure compliance with dissolved oxygen (DO) requirements of permits based on water quality
standards under Chapter 307 (relating to Surface Water Quality Standards) and Texas Water Code,
§26.023.
Proposed new §217.278, relating to Sampling Points, specifies and clarifies required sampling points,
which can be safely accessed by the wastewater treatment system operators.
Subchapter L
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Proposed new §217.290, relating to Applicability, explains that Subchapter L details the general safety
requirements which shall be followed in the design, construction, and installation of wastewater treatment
facilities.
Proposed new §217.291, relating to General Policy, explains that the design engineer shall consider
occupational safety, health hazards, and risks to the workers, other persons, and the public as part of
treatment process, disinfection, and chemical selection in preliminary and final designs.
Proposed new §217.292, relating to Safety Audit, requires, for existing facilities being modified or
expanded, the conducting of a safety audit of the facility for the prior three-year period in order to
determine the locations, causes, types of injuries, and jobs being performed when the injuries occurred.
Proposed new §217.293, relating to Job Hazard Analysis and Protective Equipment Lists, updates and
expands previous §317.7(e) and (f) requiring for increased safety that an analysis of hazardous operation
and maintenance tasks for new, expanded, or modified facilities shall be performed by the engineer in
order to develop layouts that will result in the easiest, safest, and most cost-effective way to accomplish
potentially hazardous tasks and the development of protective equipment lists.
Proposed new §217.294, relating to Railings, Ladders, Walkways, and Stairways, specifies criteria for the
use of railings, ladders, walkways, and stairways contained in safety requirements of the Occupational
Safety and Health Act, §1910.23.
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Proposed new §217.295, relating to Electrical Code, previously contained in §317.7(c), establishes that
electrical design shall conform to local electrical codes or, where there are no local electrical codes, the
design shall conform to the National Electrical Code.
Proposed new §217.296, relating to Unsafe Water, previously contained in §317.7(d), explains that when
non-potable water is made available to any part of the plant, all yard hydrants and outlets shall be properly
marked "Unsafe Water," and all underground and exposed piping shall be identified as specified in
§217.298 of this subchapter.
Proposed new §217.297, relating to Plant Protection, previously contained in §317.7(e), requires that the
plant area, including open clarifiers, aeration basins, and other open tanks, be completely fenced and have
lockable gates at all access points.
Proposed new §217.298, relating to Color Coding of Piping, previously contained in §317.7(g), is
expanded to include piping for reclaimed water and explains that all piping for new facilities shall be color
coded and provides the specified color codes.
Proposed new §217.299, relating to Portable Ventilators and Gas Detection Equipment, previously
contained in §317.7(h), requires portable, gasoline-operated ventilators to be provided for ventilating
manholes.
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Proposed new §217.300, relating to Potable Water, previously contained in §317.7(i), requires that potable
water be provided to the plant site.
Proposed new §217.301, relating to Freeze Protection, previously contained in §317.7(j), explains that all
surfaces subject to freezing shall be adequately sloped to prevent standing water.
Proposed new §217.302, relating to Noise Levels, previously contained in §317.7(k), explains that noise
levels in all working areas shall be kept below standards established by the Occupational Safety and
Health Act.
Proposed new §217.303, relating to Safety Training, clarifies previous §317.7(l) and requires that safety
training be provided annually to all employees.
Proposed new §217.304, relating to Confined Space, maintains that the design engineer shall avoid
designing or otherwise providing areas that can be considered confined spaces as described in 29 CFR
§1910.146.
Proposed new §217.305, relating to Plans and Specification Safety Review, explains new safety
requirements that the design engineer shall review the design plans and specifications to ensure
reasonable and adequate safeguards exist to eliminate and minimize worker exposure to workplace
hazards.
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Proposed new §217.306, relating to Emergency Evacuation, previously contained in §317.?? ,
incorporates Occupational Safety and Health Act requirements for emergency evacuation procedures to
be established where chlorine cylinders weighing one ton or more are located within 1/4 mile of residential
or other high density developments.
Proposed new §217.307, relating to Other Safety Design Guidelines, explains that for additional safety
design guidelines, the engineer shall refer to latest edition of Design of Municipal Treatment Plants, WEF
Manual of Practice No.8, published by the Water Environment Federation or other authoritative
documents.
RULE REVIEW
Concurrently, the commission proposes the reveiw of 30 TAC § 317, in accordance with Texas
Government Code §2001.039, and is publishing the proposed notice of review in the Rule Review Section
of the Texas Register.
Concurrently, the commission proposes the reveiw of 30 TAC § 323, in accordance with Texas
Government Code §2001.039, and is publishing the proposed notice of review in the Rule Review Section
of the Texas Register.
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FISCAL NOTE
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Stephen Minick, Strategic Planning and Appropriations Division, has determined that for the first five
years these sections as proposed are in effect, there will be fiscal implication as a result of enforcement
and administration of the sections. There are no significant implications anticipated for state government.
Local governments affected by the provisions could potentially realize cost savings as a result of adoption
of the proposed rules. The cost savings for local governments will result from better guidance on
acceptable sewage system designs and clearer flexibility for innovative technology (equipment). Local
governments may also realize a cost savings from more efficient systems built using these new criteria.
PUBLIC BENEFIT
Mr. Minick has also determined that for the first five years these sections as proposed are in effect, the
public benefit anticipated as a result of enforcement of and compliance with these sections will be
wastewater system design criteria that is clearer and more consistent with current engineering practices
and that should lead to better designed and more efficiently functioning wastewater treatment facilities.
The public should also benefit from better managed facilities and a more cost-effective regulation of
wastewater facility design and operations. There are no additional economic costs anticipated for any
person, including small business, required to comply with the sections as proposed.
DRAFT REGULATORY IMPACT ANALYSIS
The commission has reviewed the proposed rulemaking in light of the regulatory analysis requirements of
Texas Government Code, §2001.0225, and has determined that the rulemaking is not subject to
§2001.0225 because it does not meet the full applicability of a major environmental rule as defined in the
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act. The intent of the rulemaking is to update the current design criteria for wastewater facilities and is
consistent with the requirements of Texas Water Code §26.043(c). There is not a relevant standard set
by federal law. The proposed rulemaking updates existing rules and do not exceed an express
requirement of state law. There is no delegation agreement or contract directly applicable to the
proposed rulemaking.
TAKINGS IMPACT ASSESSMENT
The commission has prepared a Takings Impact Assessment for these rules pursuant to Texas
Government Code Annotated, §2007.043. The following is a summary of that assessment. The specific
purpose of the rule is to ease the burden on the commission and those regulated by the rule by revising
and updating the current design criteria for wastewater facilities. The proposed revisions will provide
clarity, flexibility, and update standards to current engineering practices. Promulgation and enforcement
of these proposed amendments will not affect private real property which is the subject of the rules.
PUBLIC HEARING
A public hearing on the proposal will be held ________________at ___________ a.m. in Room _____
of the commission Building __, located at 12100 Park 35 Circle, Austin. The hearing is structured to
receive oral or written comments by interested persons. Individuals may present oral statements, when
called upon, in the order of registration. Open discussion will not occur during the hearing; however, a
commission staff member will be available to discuss the proposal 30 minutes prior to the hearing and will
answer questions before and after the hearing.
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SUBMITTAL OF COMMENTS
Written comments on the proposal should refer to Rule Log No. 95100-317-WT and may be submitted to
Betty Bell, Texas Natural Resource Conservation Commission, Office of Environmental Policy, Analysis
and Assessment, MC 205, P.O. Box 13087, Austin, Texas 78711-3087, (512) 239-6087. Comments may
be faxed to (512) 239-5687, but must be followed up with the submission and receipt of the written
comments within three working days of when they were faxed. Written comments must be received by
5:00 p.m., ______________. The executive director is especially requesting comment as to the types
of appropriate Safety Training courses as provided by §217.303. For further information concerning this
proposal, please contact Louis C. Herrin, III, Texas Natural Resource Conservation Commission, Water
Permits and Resource Management Division, (512) 239-4552.
COASTAL MANAGEMENT PLAN
The executive director has reviewed the proposed rulemaking and found that the rule is neither identified
in Coastal Coordination Act Implementation Rules, 31 TAC §505.11, relating to Actions and Rules
Subject to the Coastal Management Program, nor will affect any action/authorization identified in Coastal
Coordination Act Implementation Rules, 31 TAC §505.11. Therefore, the proposed rule is not subject to
the CMP.
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
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provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code.
Proposed new §217.2, relating to Authority, establishes that the Texas Water Code prescribes the duties
of the commission relating to the control of pollution including the review and approval of plans and
specifications for sewage disposal systems in §§5.013, 12.081-12.083, 15.104, 15.114, 26.023, 26.034,
26.041, 49.181-49.182, 51.333, and 54.024.
There are no other rules, codes or statutes that will be affected by this proposal.
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SUBCHAPTER A : ADMINISTRATIVE PROVISIONS
§§217.1-217.19
§217.1. Applicability.
Chapter 217 applies to any person or individual who proposes to construct facilities which will
collect, transport, treat, or dispose of domestic wastewater. This subchapter details the administrative
processes which will govern the implementation of this chapter. This chapter is not applicable to facilities
constructed for the purposes of complying with a commission-issued non-domestic wastewater discharge
permit.
§217.2. Authority.
The Texas Water Code prescribes the duties of the commission relating to the control of pollution
including the review and approval of plans and specifications for sewage disposal systems. This authority
is found in Texas Water Code §§5.013, 12.081-12.083, 15.104, 15.114, 26.023, 26.034, 26.041, 49.181
49.182, 51.333, and 54.024.
§217.3. Definitions.
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The following words and terms when used in this chapter shall have the following meanings
unless the context clearly indicates otherwise.
(1) Alternative wastewater collection systems - alternative wastewater collection
systems include the categories of pressure sewers, small diameter gravity sewers, vacuum sewers, and
combinations thereof. Alternative wastewater collection systems are comprised of both on-site and
off-site components.
(2) Anaerobic biological reactor (ABR unit) - a secondary treatment unit consisting
of a mass of clean large gravel or similar media into which the primary treatment effluent is introduced in
such a manner that the media remains submerged. The treated liquid passes through the media and out of
the unit by gravity. Travel direction is usually upward from the bottom of the media mass.
(3) Annual average flow - the arithmetic average of all daily flow determinations taken
within a period of 12 consecutive months.
(4) ANSI - American National Standard Institute
(5) ASCE - American Society of Civil Engineers
(6) ASTM - American Standard Testing Material
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(7) AWWA - American Water Works Association
(8) Buffer tanks - on-site components that are used to house vacuum valves in
situations where flow quantity requires flow attenuation and/or as transition structures between
non-vacuum and vacuum systems. A buffer tank may also be used as an appurtenance with an off-site
component.
(9) Building lateral - line work that exclusively conveys raw wastewater and connects
the plumbing of a structure to an on-site component. The building lateral is not a part of the alternative
wastewater collection system.
(10) Buried filter - a filter that is constructed with a sand or soil cover. Since such
filters lose the ability for removal/replacement of filter media, the loading must be limited to rates that will
preclude media plugging.
(11) By-Pass
(12) Design flow - the permitted flow rate.
(13) Diurnal Flows
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(14) Drip irrigation - as used in this chapter, refers to the disposal of wastewater by
subsurface irrigation into soil to support vegetative growth.
(15) Drip irrigation line - a line with small emitters or applicators which is used to
dispose of wastewater at an agronomic rate by drip irrigation into the soil zone for plants for agronomic
uptake.
(16) Effective size - if a sample of filter media is examined, and the grain size plotted as
a semi-log grain size curve with the ordinates representing the percent P, by weight, of grains is smaller
than the size denoted by the abscissa, then the effective size of the sample is the diameter D10 which
corresponds to P = 10%. In other words, 10% of the sample particles are finer and 90% are larger than
the effective size.
(17) Effluent pump unit - an on-site component that provides the motive force that
conveys the effluent from an interceptor tank to either of the following:
(A) the collection system in Small Diameter Effluent Sewer (SDES) systems; or
(B) the terminus of the collection system, in pressure systems.
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(18) Engineer - the design engineer who is licensed by the Texas Board of Professional
Engineers.
(19) Equivalent dwelling unit (EDU) - a single, private residence, or a commercial
establishment which produces wastewater of a composition and quantity comparable to that discharged by
a single, private residence.
(20) Facility – a wastewater treatment system.
(21) Filter media - the material placed in the filter containment structure to perform the
filtering action. Materials used as filter media include natural or manmade sand, bottom ash, crushed slag,
fine gravel, etc.
(22) Firm Pumping Capacity - the maximum flowrate under design conditions with the
largest pumping unit out of service.
(23) Force main - a pressure-rated conduit which conveys wastewater from a pump
station to a discharge point.
(24) fps - feet per second
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(25) Grinder pump unit - an on-site component that receives raw wastewater by a
building lateral, grinds the solids present in the raw wastewater into a slurry, and provides the motive
force for transporting the raw wastewater to the terminus of the collection system.
(26) Innovative technology - a process not addressed in this chapter, or a process
specifically identified as innovative by this chapter.
(27) Interceptor tank - an on-site component that receives raw wastewater by a
building lateral, and provides removal of floatable and settleable solids, storage of the removed solids, and
flow attenuation.
(28) Intermittent or single pass filter - a filter through which the water being filtered
passes one time.
(29) Lateral sewer - a sewer running laterally down a street, alley, or easement which
receives only the flow from the abutting properties.
(30) Lift Station
(31) Manager/Operator of the alternative wastewater collection system - a
political subdivision of the State, water supply or sewer service corporation, or other legal entity under the
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regulatory jurisdiction of the commission that is authorized to own, operate, and/or maintain a wastewater
system as a public utility.
(32) mgd - million gallons per day.
(33) Multiple equivalent dwelling unit (MEDU) - is either a group of single, private
residences served by a common on-site component, or a commercial, industrial, institutional, or other
non-residential establishment that produces wastewater in excess of 1500 gallons per day and/or
wastewater of a composition not comparable to that discharged by a single, private residence.
(34) Nonconforming technology - technology or a process that does not conform to the
design criteria of this chapter, or a technology or process specifically identified as nonconforming by this
chapter.
(35) Off-site components - include collection system lines and related appurtenances,
forcemains, pump stations, lift stations, and vacuum stations.
(36) On-site component - interceptor tanks, effluent pump and grinder pump units,
vacuum valve pits and buffer tanks, and their service lines.
(37) Overflows
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(38) Peak flow - the highest two-hour flow expected to be encountered under any
operational conditions, including times of high rainfall (generally the two-year 24-hour storm is assumed)
and prolonged periods of wet weather.
(39) Person - an individual, association, partnership, corporation, municipality, state, or
federal agency, or an agent or employee thereof.
(40) Point of application - point at which wastewater enters native soil except in the
case of mound systems where it is the point where wastewater enters engineered soil material.
(41) Pressure sewers - a sewer that is entirely pressurized by pumps at each service
connection. It is differentiated into grinder pump and septic tank effluent pump (STEP) sewers. A grinder
pump pressure sewer receives raw wastewater in which the solids have been ground by a grinder pump.
A STEP pressure sewer receives the effluent from an interceptor tank.
(42) Private sewer - a closed conduit which conveys wastewater flow and is
constructed and maintained by a private entity(ies) such as a homeowner's association. Private sewers
may be located in areas such as a private street or common area.
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(43) Public sewer - a closed conduit which conveys wastewater flow and which is
located within the public right-of-way or dedicated public easement. A public sewer (or public sewer
system) is intended to serve more than one (1) owner.
(44) Recirculating filter - a filter that is loaded by a mixture of unfiltered and
previously filtered water.
(45) REACT - a step in the Sequencing Batch Reactor (SBR) process where the
influent in the SBR basin is aerated.
(46) Sand filter - a contained mass of sand or other equivalent media to which water
may be applied such that the water will pass through the sand resulting in the removal of water borne
materials such as organic debris, bacteria, or grit, and reduction of the amounts of dissolved nutrients.
The sand filter consists of the containment structure, an underdrain piping network, the underdrain media,
the filter media, and a liquid distribution mechanism to spread the load over the filter surface.
(47) Sequencing Batch Reactor (SBR) - a fill and draw activated sludge treatment
system, identical to conventional activated sludge systems, except the processes are carried out
sequentially in the same tank. SBR systems have the following five steps carried out in sequence.
(A) Fill - The basin is filled with the influent;
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(B) React - The influent in the basin is aerated;
(C) Settle - The mixed liquor within the basin is settled (clarification);
(D) Draw - The basin is decanted; and,
(E) Idle - The sludge is wasted from the basin.
(48) Service connection - a private sewer from a single source to the main or lateral
sewer in the street, alley, or adjacent easement.
(49) Service lead - a sewer which branches off a public sewer and extends to the
limits of the public right-of-way. From a main or lateral sewer, the service lead would serve one or more
houses, single-family lots, or other types of small land tracts situated in the same block with the main or
lateral sewer, but not directly adjacent thereto. Such a line, shall never exceed 150 feet in length. If the
sewer is designed to serve more than two houses, or the equivalent of two single-family residences along
a street, a lateral sewer as defined above shall be constructed.
(50) Service line - the service line is the line work that hydraulically connects an on-site
component to the off-site components and is a part of the alternative wastewater collection system.
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(51) Sewer main - a sewer which receives the flow from one or more lateral sewers.
(52) Small diameter effluent sewers (SDES) - sewers that receive effluent from an
interceptor tank and transport the flow by gravity. SDES are differentiated into minimum grade effluent
sewers (MGES) and variable grade effluent sewers (VGES). MGES are designed with a constant
downward slope. A VGES has no slope restrictions except that effluent should shall not flow back into
any service connection.
(53) Uni-Bell -
(54) Uniformity coefficient - the uniformity coefficient (U) is equal to the ratio
D60/D10: D60 is the grain size corresponding to P = 60% on the plot of sample grain size, and D10 is the
grain size corresponding to P = 10% on the plot of sample grain size. A low uniformity coefficient
indicates a uniform grain size in a sample, while a high value indicates a wide variation in grain size.
(55) Vacuum valve pit - a vacuum valve pit is an on-site component that receives raw
sewage by a building lateral and provides detention until accumulation of such volume to instigate
operation of the vacuum valve. For EDUs as defined above, the vacuum valve pit and vacuum valve shall
be an integral unit.
(56) Variance - a deviation from a specific requirement of this chapter.
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(57) Wastewater treatment system - all on site treatment components including but not
limited to lift stations; treatment facilities; primary, secondary, tertiary treatment; and sludge treatment.
(58) WEF – Water Environment Federation
§217.4. Purpose.
These design criteria are minimum requirements which shall be used for the comprehensive
design of domestic sewage collection, treatment, or disposal systems. This chapter establishes the
minimum design criteria pertaining to effluent quality necessary to meet state water quality standards.
These minimum criteria may not be appropriate for certain design situations. The design engineer shall
use best professional engineering judgement to determine whether the criteria set forth in this chapter are
sufficient to meet the public health and water quality requirements as established by the commission.
The executive director may require more stringent criteria where, in the executive director’s judgement,
the use is necessary to meet public health and water quality goals. Plans, specifications, and final
engineering design reports for a proposed project shall conform to the requirements of this chapter.
§217.5. Variances.
A variance is a deviation from a specific requirement of this chapter. An example of a variance
is the use of a slightly flatter slope for a pipe than the minimum slope prescribed by this chapter in order to
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maintain the minimum separation distance between the proposed wastewater line and an existing water
line. All known variances from the requirements of this chapter shall be disclosed to the executive
director or appropriate review authority at the time that project related materials are submitted. Variances
which are incorporated into the project after construction begins, shall be disclosed to the executive
director or appropriate review authority in the completion certification required by §217.13 of this title
(relating to Completion Notification). All variance disclosures shall be made under the seal of a
professional engineer licensed in the State of Texas and shall state that based on the best professional
engineering judgement of the engineer, the variance will not result in a risk to public health or water
quality. A technical justification for any variances shall also be included under the professional engineer’s
seal. The executive director may request further information regarding any variance disclosures. If, as
determined by the executive director, the variance would result in a situation which would contradict the
state public health and water quality requirements, the executive director may deny the variance, or,
require further measures to be taken by the owner. If the executive director does not, within ten working
days of receiving a signed, dated, and sealed variance disclosure, notify the engineer by fax or letter, that
further information is requested, or, that the variance is denied, the variance shall be considered to be
approved. A variance shall not be granted or approved from any prohibition included within this chapter.
§217.6. Relationship between Plans and Specifications Approval and Wastewater Discharge
Permits.
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(a) Plans and specifications approvals shall correspond precisely to the flow and effluent
limitations set forth in the associated discharge permit. A plans and specifications approval may
correspond to any of the existing permit phases. If plans and specifications approval at an interim phase
is obtained, an additional plans and specifications approval shall be requested before the
facility may begin operating at the next permit phase.
(b) Approval of plans and specifications in accordance with this chapter does not relieve the
owner of a wastewater treatment facility of the responsibility to obtain a wastewater discharge permit or
other authorization in accordance with Chapter 26 of the Texas Water Code. In no case shall bypassing
of partially treated wastewater be authorized during construction without an order for such discharge.
(c) Commission approval of a wastewater discharge permit does not relieve the owner of a
wastewater treatment facility of the responsibility to obtain plans and specifications approval of that
facility, in accordance with this chapter, prior to discharge.
§217.7. Construction of Approved Facilities.
(a) Approval of plans and specifications by the Executive Director does not imply that
construction of the facilities may begin. Construction shall not begin on any approved wastewater
treatment facility until a wastewater discharge permit has been issued by the commission, unless the
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commission authorized the applicant to construct prior to permit issuance, pursuant to Texas Water Code,
§26.027.
(b) Phased construction of wastewater treatment facilities shall correspond to phases included in
the associated wastewater discharge permit. If other types of phased construction are desired, the
engineer shall disclose this phased construction and request a variance from this subsection through
§217.5 of this title (relating to Variance Clause).
§217.8. Pre-existing Facilities.
(a) Any facilities which were constructed in accordance with a plans and specifications approval
granted prior to the effective date of these rules, which are not being modified in any way, and for which
no design related permit changes have been made, or, are proposed, shall not be required to comply with
the requirements of this chapter. These facilities are required to meet the standards and criteria
established at the time of the original plans and specifications approval, along with any wastewater
discharge permit requirements.
(b) New facilities or any modifications to existing facilities shall comply with the requirements of
the chapter which is effective on the date the plans and specifications are submitted.
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(c) New facilities which are proposed for construction shall comply with the requirements of this
chapter.
(d) Existing facilities, which have never received a plans and specifications approval, shall
comply with the requirements of this chapter.
§217.9. Submittal Requirements.
(a) All proposed wastewater projects shall submit a summary transmittal letter, which conforms
to the requirements found in subsection (c) of this section to the TNRCC Water Permits and Resource
Management Division, except as provided by §217.11(b) of this title (relating to Municipality Reviews)
(b) Wastewater projects which receive a technical review for compliance with this chapter and
approval from a state agency other than the TNRCC need not be submitted to the agency for review, if
under the following conditions:
(1) the review is performed under the supervision of a professional engineer licensed in
the State of Texas, and the review ensures that the project substantially complies with this chapter, and
(2) the state agency has been granted authority in lieu of the commission under state
law.
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(c) A summary transmittal letter shall be submitted, by certified mail, to the Commission’s
Wastewater Permitting Section, and to the TNRCC Regional Office in which the project will be located,
for all other wastewater projects constructed in the State of Texas. If the executive director does not
notify the person who submitted the summary within 10 working days of receipt of submittal that a review
will occur, under subsection (d) of this section, the project is deemed approved. The information in the
summary shall be signed, dated, and sealed by a professional engineer licensed in the State of Texas. All
summaries shall include, at a minimum:
(1) the name and address of the design firm;
(2) the name, phone number, and facsimile number of the engineer;
(3) the county(s) in which the project will be located with an identifying name for the
project;
(4) the name of the entity which proposes to own, operate, and maintain the project
through its design life;
(5) the permit name and permit number of the relevant wastewater treatment facility;
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(6) a statement verifying that the plans and specifications are in substantial compliance
with all the requirements of this chapter and which states that any deviations from the requirements are
based on the best professional judgement of the licensed professional engineer who prepared the final
engineering design report and the project plans and specifications;
(7) a brief description of the project scope which includes the specifics of the project, a
description of deviations variances from the requirements of this chapter, including the use of non
conforming or innovative technology, and an explanation of the reasons for such deviations which is
sufficient to satisfy the requirements of §217.5 of this title (relating to Variance Clause).
(d) Any project is subject to review by the executive director. Factors to be used to determine
whether a review will be performed include, but are not limited to, the following: whether or not a
nonconforming or innovative technology is being proposed; the stream segment in which the project is
located; and the applicant’s compliance record. If the executive director chooses to review a project, the
engineer or project owner shall be notified in writing, or by facsimile, of the executive director’s intent to
review the project within ten days of receipt of the summary. Upon receipt of the notification of intent to
review, the engineer shall submit to the executive director a complete set of plans and specifications and a
complete final engineering design report. These submitted materials shall be sufficient to satisfy the
executive director that the project is in substantial compliance with this chapter. If the executive director
reviews a project, approval may be granted in accordance with §217.10 of this title (relating to Types of
Approvals).
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(e) A complete set of plans and specifications, the final version of such plans and specifications
with engineer's certification, a complete engineering design report, all change orders and test results, a
copy of the written summary submitted to the executive director, and any written approvals granted by the
executive director, a municipality, or another state agency shall be maintained and kept by the permittee,
or person(s) responsible for management of a collection system if not the permittee, for at least three
years from the date the engineer certifies to the executive director that the project is complete. Any or all
of this material shall be submitted to the executive director, another state agency, or municipality upon
request. Such materials shall be readily available for inspection by executive director staff upon request
during regular business hours.
§217.10. Types of Approvals.
Approval given by the executive director, or a participating municipality or state agency with
review authority as provided for in §217.9 of this title (relating to Submittal Requirements), shall not
relieve the sewerage system owner or the engineer of any liabilities or responsibilities with respect to the
proper design, construction, or authorized operation of the project in accordance with applicable
commission rules. Regardless of the type of approval, constructed facilities when in operation are required
to produce the quality of effluent specified in the facilities discharge permit(s). The types of approvals
described in paragraphs (1)-(3) of this section may be utilized by the executive director or any other
review authority.
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(1) Standard approval. Plans and specifications found to comply with all applicable parts
of these criteria shall be approved for construction.
(2) Approvals of innovative and nonconforming technologies.
(A) Technologies considered to be nonconforming or innovative include, but are
not limited to, those technologies not conforming to or addressed in the design criteria of this chapter.
Innovative technology is technology or a process not addressed the design criteria of this chapter, or a
technology or process specifically identified as innovative by this chapter. Nonconforming technology is a
technology or process that does not conform to the design criteria of this chapter, or a technology or
process specifically identified as nonconforming by this chapter. An example of a nonconforming
technology is the use of a trickling filter as a once-through roughing filter.
(B) If an approval for nonconforming or innovative technologies is requested,
engineering proposals for processes, equipment, or construction materials shall be fully described in the
summary transmittal letter submitted in accordance with §217.9(c) of this title, and the reasons for their
selection clearly outlined. The requestor shall wait for written approval from the executive director prior
to proceeding with any innovative or nonconforming technology. Prior to approval or disapproving of the
request the executive director may request a full review of a project which contains innovative or
nonconforming technology. Approval of processes, equipment, or construction materials which are
considered to be innovative or nonconforming shall be granted only in cases where the executive director
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or review authority determines, after an engineering evaluation of the supporting information provided in
the submitting engineer’s design report, that the technology will not result in a threat to public health or the
environment. The executive director may require processes considered to be nonconforming or
innovative to be supported by results of pilot or demonstration studies. Where similarly designed full scale
processes exist and are known to have operated for a reasonable period of time under conditions similar
to those suggested for the proposed design, performance data from these existing full scale facilities shall
be submitted at the executive director’s request in addition to, or in lieu of, pilot or small scale
demonstration studies. Any warranties or performance bond agreements offered by the process,
equipment, or material manufacturers shall be fully described in the summary transmittal letter.
(C) The executive director or review authority may require the manufacturer or
supplier to obtain and furnish evidence of an acceptable two-year performance bond from an approved
surety which insures the performance of the innovative or nonconforming technology. The two-year
period shall commence upon substantial completion. Determination of substantial completion will be by a
licensed professional engineer designated by the owners. The executive director will consider as an
acceptable performance bond one which covers the full cost of removal or abandonment of the innovative
or nonconforming facility and equipment, the replacement with previously agreed upon facilities or
equipment conforming to these rules, and all associated engineering fees necessary for the removal and
replacement.
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(D) Approval of innovative and nonconforming technologies may include a
condition which states that, after some predetermined period of time after the installation and startup of
the innovative or nonconforming technology, an engineering report detailing the performance of the
nonconforming or innovative technology shall be submitted. The engineering report shall include objective
calculations and data detailing the technology's performance, and written submittals from the engineer and
the permittee which state that the nonconforming or innovative technology has satisfied the
manufacturer's claims.
(3) Conditional approval. The executive director may grant approvals which contain detailed
conditions, stipulations, or restrictions. Examples of such conditions and stipulations include, but are not
limited to, testing requirements, reporting requirements, operational requirements, and additional installation
and design requirements which may be necessary to ensure compliance with this chapter. Any
conditional approval granted may be issued for a specific set of flow situations, wastewater
characteristics, and/or required effluent quality. If a conditional approval is granted, both the sewage
system owner and engineer, as appropriate, shall be responsible for ensuring that the approval conditions
outlined by the executive director have been met.
§217.11. Municipality Reviews.
(a) Municipalities may perform technical reviews of sanitary sewer collection systems under
Texas Water Code, §26,034. If a municipality decides to perform technical reviews of sanitary sewer
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collection systems after the effective date of this rule, the municipality shall submit 30 days prior to
commencing review to the executive director maps clearly delineating the jurisdictional boundary of the
municipality for the area for which they will be responsible for review of plans and specifications. Within
90 days of a change in the boundary of the municipality, the review authority shall submit maps to the
executive director detailing the boundaries of the review authority. If at any time a municipality, which
has chosen to implement this review authority, decides to cease review of sanitary sewer collection
system plans and specifications, the municipality shall provide written notice to the executive director at
least 30 days prior to the date on which cessation of the final plans and specifications review is expected
to occur. Municipalities shall incorporate the items detailed in paragraphs (1)-(5) of this subsection into
their review programs.
(1) The municipality’s review and approval process shall ensure substantial compliance
with the rules of this Chapter.
(2) All reviews performed by an employee of the municipality shall be conducted by a
professional engineer, licensed in the State of Texas, or the employee conducting the review shall be
under the direct supervision of a professional engineer, licensed in the State of Texas, who is ultimately
responsible for the review and approval of each collection system submitted and installed in the
municipality’s jurisdiction.
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(3) The responsible review engineer shall be either an employee of the reviewing
municipality, or a consultant to the municipality, separate from the private consulting firm charged with the
design work under review. For purposes of this section, the term "separate" means that the responsible
review engineer is not employed by and does not receive any compensation from the private consulting
firm or from any parent companies, subsidiaries, or affiliates charged with the design. The municipality
shall provide the executive director, on request, documentation of agreements with private consultants
sufficient to allow the agency to audit the municipality’s compliance with this subsection.
(4) A participating municipality may review and approve engineering reports, plans, and
specifications only for projects which transport primarily domestic waste within the boundaries of
jurisdiction of that municipality. For each project approved for construction, the municipality shall issue an
approval letter or other indication of the approval which clearly details the project being approved.
(5) The municipality shall maintain complete files of all review and approval activities
carried out under its authority and shall make any existing project files available to the executive director
upon request and/or during audits performed in accordance with subsection (b) of this section.
(b) The executive director may perform periodic audits of the review and approval process of
municipalities, which perform technical reviews of sanitary sewer collection systems in lieu of the
executive director, to ensure that the projects approved by the municipalities are in substantial compliance
with this chapter. If the executive director decides to perform an audit of a municipality's review and
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approval process, the executive director will provide the municipality with a minimum of five working days
advance notice of the pending audit. The executive director may, for auditing purposes only, review
specific projects which have previously been approved by the review authority. The municipality shall
provide to the executive director, on request, documentation of all agreements between the private
consultants and the municipality which relate to the wastewater collection system review program. If the
executive director finds through reviews of specific projects or through audits of the municipality's review
and approval process that a municipality's review and approval process does not provide for compliance
with the minimum design and installation requirements detailed in this chapter, the review and approval
authority shall address these findings within a time established by the executive director. If compliance
cannot be achieved, the review authority shall be voided for that municipality. If such authority is voided
for a municipality, the executive director shall notify the municipality in writing and shall include the
justification for voiding the authority of the municipality. If the authority of a municipality is voided, all
new projects proposed to be constructed within that municipality’s jurisdiction shall be submitted to the
executive director in accordance with §217.9(c) of this title (relating to Submittal Requirements). If the
authority of a municipality is voided, then the municipality shall inform all new projects of the requirement
to seek approval from the commission.
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§217.12. Substantial Design Changes.
If substantial design change occur for a project after an approval has been granted, the engineer
shall notify the executive director or review authority with a written description of the extent of the
changes. The notification shall have the signed and dated seal of a professional engineer licensed in the
State of Texas. The determination of what constitutes a substantial design change shall be made by the
engineer based on best professional judgement. The executive director or review authority may request
additional information regarding the project design change. The executive director or review authority
may perform a technical review of these changes to ensure that the changes will meet its public health
and water quality requirements. If the executive director or review authority does not request information
from the engineer by mail or facsimile within 10 working days of receiving a signed, dated, and sealed
notification, the changes shall be considered to be approved.
§217.13. Completion Notification.
Upon completion of construction of any wastewater facility constructed in the State of Texas, the
design engineer, or other engineer appointed by the owner, shall provide a notice to the executive director
or the review authority which is signed, sealed, and dated by a professional engineer licensed in the State
of Texas, and which attests that the completed work substantially complies with the approved plans,
specifications, and any approved substantial design changes, and the O & M Manual has been prepared
and delivered.
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§217.14. Inspection.
During construction, any wastewater project is subject to inspection by the executive director or
the review authority during normal working hours to determine compliance with this chapter, the project
plans and specifications, the final engineering design report, and any approval letters.
§217.15. Operation and Maintenance Manual.
An operations and maintenance (O&M) manual shall be developed by the engineer for any
wastewater facility. The O&M manual shall include information specific to the designed project
necessary to promote efficient and safe operations and maintenance, monitoring, and reporting by the
operators. The engineer shall provide the owner of the proposed facility, and the operator who will be
responsible for operation and maintenance of the wastewater treatment facility, the opportunity to make
comments and recommendations to the O&M manual before the manual is finalized. A copy of the final
version of the O&M manual shall be kept by the owner of the facility and at the wastewater treatment
facility, and shall be submitted to the executive director upon request. If during the course of operations it
is determined that the original O&M manual is in error or requires updating, copies of any amendments to
the O&M manual shall also be kept by the owner at the treatment plant site. The following items shall be
considered to be included in the O&M manual:
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(1) Administrative and record keeping items such as a table of contents showing the
location of the contents within the manual; a copy of the wastewater discharge permit; names and
telephone numbers for pertinent contacts within the appropriate state and federal regulatory agencies; a
sample of a typical Monthly Effluent Report applicable for the size and type of facility proposed; a sample
daily activity report that contains spaces for the results of any internal monitoring done in association with
internal process control, such as flow rates from the various units, dissolved oxygen levels, pH, solids
concentrations, settling test results, clarifier sludge blanket depths, sludge age or retention time and
disinfection residuals; and, a description of the quality assurance/quality control record keeping
requirements for all laboratory analyses performed. This daily activity report may be modified by the
operators to include additional necessary information;
(2) Operation and maintenance requirements such as a section describing the typical
flow pattern within the facility, including the size and capacity of all units; the typical start-up procedures,
routine operational procedures and shut-down procedures for all units; a description of the manner in
which solids are returned to aeration or wasted and the expected volumes under various flow conditions;
expected solids concentrations in all units; expected clarifier overflow rates; expected disinfectant and
dechlorination usage and dosage amounts during normal and emergency operating conditions; descriptions
and frequencies of routine in-situ and laboratory analyses to be performed, including a list of references to
standard testing procedures literature; descriptions of routine maintenance activities to be performed,
including lubrication and inspection schedules for all pumps, motors, and other equipment; and a
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recommended spare parts inventory with the names and telephone numbers of manufacturers and
suppliers; and,
(3) Safety items such as a discussion of all known or reasonably anticipated safety
hazards within the facility and a description of the location and the method of use for all personal safety
equipment; and a discussion of emergency evacuation plans including appropriate contact names and
phone numbers of entities or individuals to be contacted during emergency situations including chemical
releases.
§217.16. Operational Considerations.
The engineer shall consult with the relevant operations staff during the design of the project. The
design shall include design elements which are desired by the operations staff when, in the best
professional judgement of the engineer, such design elements are practical. When construction, startup,
and shutdown situations threaten a facility’s ability to remain in compliance with its discharge permit,
engineering staff and operational staff shall communicate sufficiently to minimize danger to public health
and water quality during these periods.
§217.17. Final Engineering Design Report.
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A final engineering design report shall be developed for any wastewater facilities constructed in
the State of Texas. This report shall bear the signed and dated seal of a professional engineer licensed in
the State of Texas who is responsible for the design. The final engineering design report shall include any
calculations, analyses, graphs, formulas, constants, tables, geologic information, hydraulic and hydrological
information, historical data, and technical assumptions which are needed to show compliance with this
chapter, or, to justify variances from this chapter in accordance with §217.5 of this title (relating to
Variance Clause). At a minimum the following items, as determined to be applicable to the project by the
engineer, shall be included in the final engineering design reports.
(1) Collection Systems (if applicable) shall include the following:
(A) a map which shows the existing service area and the area proposed for
service;
(B) terrain data in sufficient detail to establish general topographical features of
present and future areas to be served;
(C) details which explain how the design flow for the system was determined;
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(D) minimum and maximum grades for each size and type of pipe and
calculations which show the expected minimum and maximum velocities in the piping system for each size
and type of pipe;
(E) the effect of any proposed system expansions on the existing system
capacity for both lift stations and piping;
(F) amount of existing and anticipated inflow/infiltration, its hydraulic effect on
the proposed and existing system, and, if needed, flow monitoring and inflow/infiltration abatement
measures which will be taken to help ensure a properly functioning system;
(G) the capability of the existing trunk and interceptor sewers and lift stations to
handle the peak flow under anticipated conditions and the capability of existing treatment facilities to
receive and adequately treat the anticipated peak flows;
(H) engineering analyses which show compliance with the pipe design
requirements of §217.53 of this title (relating to Manholes and Related Structures), regarding structural
design and minimization of odorous conditions;
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(I) a description of the areas not served by the present proposed project, and the
projected means of providing service to these areas, including special provisions incorporated in the
present plans for future expansion;
(J) calculations and curves which show the operating characteristics of any
system lift stations at minimum, maximum and design flows during both present and future conditions; and,
(K) the safety considerations which have been incorporated into the project
design such as ventilation, entrances, working areas and prevention of explosions.
(2) Wastewater Treatment Facilities (if applicable) shall include the following:
(A) Quantity and characteristics of existing wastewater influent and changes in
characteristics anticipated in the future. If adequate records are not available, analyses shall be made for
the existing conditions and such information included in the report;
(B) Facility siting information which includes: a map and/or sketch with the
location of the proposed wastewater treatment facility, the area included in the facility site, the area that
makes up the dedicated buffer zone and the area surrounding the wastewater treatment facility; a
description of the surrounding area that discloses present and future housing developments, industrial sites,
prevailing winds, highways and/or public thoroughfares, water treatment facilities, water supply wells and
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intakes, parks, schools, recreational areas, and shopping centers; the location of the wastewater discharge
which includes the immediate receiving stream, canal, major water course, or other waters in the state
which will receive the wastewater; or the acreage which will be used for disposal of effluent if not by
discharge to waters in the state. Additionally, the siting information shall include:
(i) All documentation necessary to show full compliance with the buffer
zone criteria specified in §309.13 of this title (relating to Unsuitable Site Characteristics); and
(ii) All documentation necessary to show full compliance with the 100
year flood plain restrictions specified in §309.13 of this title.
(C) A sewage sludge management plan which includes the estimated quantity of
sewage sludge that will be handled, including future sewage sludge loads based on flow projections; the
quality and sewage sludge treatment requirements for ultimate disposal, the sewage sludge storage
requirements for each alternative; the method of sewage sludge transport, the method of sewage sludge
use, storage and disposal; and what alternatives, contingencies and mitigation plans exist to ensure reliable
capacity and operational flexibility;
(D) Methods to address control of bypassing such as information and data
describing features (such as auxiliary power, standby and duplicate units, holding tanks, storm water
clarifiers or flow equalization basins) and operational arrangements (such as flexibility of piping and valves
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to control flow through the treatment units, reliability of power sources) to prevent unauthorized
discharges of untreated or partially treated wastewater during construction; and,
(E) All information and calculations to show that the wastewater treatment
facility design complies with the requirements of this chapter such as the types of units proposed and their
capacities; the detention times, surface loadings, and weir loadings as pertinent to the wastewater
treatment units; and hydraulic profiles for wastewater and sewage sludge which includes a plot of the
hydraulic gradient at peak flow conditions for all gravity lines, the anticipated operation mode of the
treatment facility, organic and volumetric loadings as pertinent to specific units, aeration demands and
how those demands will be supplied, and any other calculations deemed necessary by the engineer, or the
executive director, to show compliance with the requirements of this chapter.
§217.18. Final Construction Drawings and Technical Specifications.
Construction drawings and technical specifications shall be prepared for any wastewater
treatment facility constructed in the State of Texas. The drawings shall include the signed and dated seal
of a professional engineer licensed in the State of Texas, who is responsible for the wastewater treatment
facility design, on each sheet which contains items relevant to the rules of this chapter. The technical
specifications for the project shall be bound together and shall include the signed and dated seal of a
professional engineer licensed in the State of Texas, who is responsible for the wastewater treatment
facility design, on the title page. The final construction drawings and technical specifications shall include,
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at a minimum, all of the items in paragraphs (1)-(3) of this section, which the engineer determines is
applicable to the project. The executive director or review authority may request more information as
needed to allow a review of the project to be performed.
(1) The construction drawings for wastewater collection systems shall include plan and
profile drawings for both gravity lines and pressure piping. Each sheet of the drawings shall be prepared
using a vertical and horizontal scale which is clearly identified on the drawings. The construction
drawings shall specify the size, grade, and type of pipe materials, the location of any structural features of
the collection system, including manholes to be installed, waterway crossings, bridge crossings, siphons, lift
station locations, and air release valves. The construction drawings shall show the location of all potable
water distribution lines which are 9 feet or closer to any portion of the wastewater collection system, and
indicate the separation distances between such lines and the wastewater collection system. The drawings
shall include dimension section details of manholes, manhole covers, and any other collection piping
appurtenances the engineer deems necessary. The drawings for any lift stations shall show the location
of all pumps, valves, pumping control equipment, safety and ventilation equipment; access operator points;
hatches and hoisting equipment for installing; and removing equipment, slope and location of any wet well
floor grouting, valve vaults, valve vault piping and gas migration prevention measures used between the
wet well and the valve vault; location of piping entrances and exits; location of sump pumps; levels of float
switches; and any other lift station related appurtenances the engineer deems necessary.
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(2) The construction drawings for the wastewater treatment facility shall include plan
and profile drawings of all piping and treatment units applicable to the project. Each sheet of the
drawings shall be prepared using a vertical and horizontal scale which is clearly identified on the
drawings. The construction drawings shall include the dimensions of all wastewater treatment units
applicable to the project. The construction drawings shall include all mechanical, electrical, and
construction details applicable to the project. Details of piping systems which the engineer determines to
be complex may be clarified by inclusion of an isometric flow diagram as part of the construction
drawings. The construction drawings shall include a hydraulic profile of the treatment facility at both
design and peak flows. The engineer shall consider including provisions for future expansion of the plant.
(3) As applicable, the specifications for the collection system and the wastewater
treatment facility shall include technical descriptions of all equipment including the quantity and sizes of
the equipment. The specifications shall also include any applicable materials specifications, installation
procedures, construction, and installation safety measures, testing requirements, and national standards
citations.
§217.19. Compliance With Other Regulations.
The rules in this chapter constitute the design criteria promulgated to implement the state statutes
detailed in §217.2 of this title (relating to Authority). These rules do not supersede or replace any other
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state statutes or local or federal requirements such as EPA requirements, OSHA requirements, or the
requirements of the Uniform Fire Code. It shall be noted, however, that the agency shall not be
responsible for interpreting, reviewing, or enforcing these rules and regulations, or any other rules and
regulations which are not implemented under the authority provided to the agency by the Texas Water
Code or other legislative directives.
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SUBCHAPTER B : DESIGN REQUIREMENTS
§§217.31-217.37
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code as well as the authority to set standards to prevent the
discharge of waste that is injurious to the public health under §26.041 of the Texas Water Code.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.31. Applicability.
This subchapter details the design values which shall be utilized by the engineer when determining
the sizes of the wastewater treatment system components. This subchapter applies to all wastewater
treatment system designs including new facilities, upgrades of existing facilities, and re-ratings of existing
facilities.
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§217.32. Design of New Systems - Organic Loadings and Flows.
For new systems being constructed to serve the same service area as an existing plant, §217.33
of this title (relating to Design of Existing Systems - Organic Loadings and Flow) may be utilized for
design, provided sufficient data exists. In the absence of sufficient data, new systems shall be designed
using the flows and loadings in paragraphs (1)-(3) of this section. These values are permitted flows and
loading concentrations which include an allowance for some infiltration.
(1) Design flow. The design flow is the permitted flow. Permitted flow is the average
annual flow value, determined by multiplying the per capita flow in Table B.1 by the number of people in
the service area, for facilities equal to or greater than one million gallons per day (mgd). For facilities less
than one mgd, the permitted flow is the maximum 30-day average flow. The maximum 30-day average
flow may be estimated by be multiplying the average annual flow by a factor of 1.5 or greater.
(2) Two-hour peak flow. The instantaneous two-hour peak flow shall be estimated by
multiplying the permitted flow by a factor of 5 for flows less than 0.5 mgd, and by a factor of 4 for flows
of greater than or equal to 0.5 mgd; unless, the system experiences unusual diurnal and/or seasonal
variations, in which case a higher ratio may be needed, as determined by the engineer. In certain regions
or systems with flow equalization, the facility may be designed for a lower ratio if the engineer provides
supporting data. The supporting data in case of region justification should include flow data from at least
three similar wastewater treatment systems from the region. All treatment units, pipes, weirs, flumes,
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disinfection units or any other treatment unit which is flow limited shall be sized to transport and/or treat
this estimated two-hour peak flow. The treatment facility shall utilize a totalizing flow meter for flow
measurement regardless of size of the facility.
(3) Design Organic Loading. The design organic loading shall be used in design, when
data is not available. The design organic load shall be determined by multiplying the projected uses by
annual average flow determined from Table B.1. of this section and by using the appropriate influent
concentration found in Table B.1. This design organic load is the load which shall be used to determine
the size of any treatment units which are intended to provide treatment of organic wastes. (Figure 1:
§217.32 (3))
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Table B.1 - Design Organic Loadings and Flows for New Wastewater Treatment Systems
Source Remarks Daily Wastewater Flow
(Gallons Per Person)
Wastewater Strength
(mg/L BOD5)
Duration of Flow
(Hours)
Municipality Residential 100 200 24
Subdivision Residential 100 200 24
Trailer Park
(Transient)
2½ Persons per
Trailer
50 300 16
Mobile Home
Park
3 Persons per Trailer 75 300 24
School with
Cafeteria
With Showers
Without Showers
20
15
300
300
8 - 12
8 - 12
Recreational
Parks
Overnight User
Day User
30
5
200
100
16
16
Office Building or
Factory
--- 20 300 Length of Shift
NOTE: The facility
shall be designed for
largest shift.
Motel --- 50 300 12
Restaurant Per Meal 5 1000* 12
Hospital Per Bed 200 300 12 - 24
Nursing Home Per Bed 100 300 12 - 24
Alternative
Collection
Systems
(Subchapter D)
Per Capita 75 N/A 24
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*Based on restaurant with grease trap
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§217.33. Design of Existing Systems - Organic Loadings and Flows.
Existing systems which are being modified or re-rated to meet new permit conditions shall use
historical data as the design basis for justifying the sizing of existing or proposed wastewater treatment
system components. The compiled data must meet the criteria outlined in paragraphs (1) and (2) of this
section.
(1) Flows. When an existing treatment plant is to be re-rated, expanded, or upgraded,
the volume of existing flow shall be determined. At a minimum, the existing plant’s past five years of data
shall be reviewed, and the engineer shall include the calculations and assumptions which were used to
determine the annual average flow, the maximum monthly 30-day average flow, the peak 2-hour flow, the
ratio of maximum monthly 30-day average flow to annual average flow, and the ratio of the peak 2-hour
flow to the annual average flow in the engineering design report. The analysis for the 2-hour peak flow
shall be based on a frequency distribution analysis based on one of the methodologies outlined in
paragraphs (A), (B), or (C) of this section. The flow data for these analyses shall be collected by a
totalizing meter regardless of plant size. The engineering design report shall note the service area of
existing development and future development.
(A) The flow charts for the individual day shall be examined to determine the
maximum sustained flow rate over any 2-hour period.
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(B) Instantaneous flow rates at one hour intervals shall be utilized to calculate
progressive 2 hour interval volumes in order to determine maximum volume for any 2-hour interval for
each day. Based on individual 2-hour peak flow values, a frequency distribution shall be utilized with the
2-hour peak flow not exceeded 98% of the time to be used to determine the ratio of 2-hour peak flow to
the annual average flow. Utilizing this historical ratio, the 2-hour peak flow for the proposed facility may
be predicted. This prediction is based on no major flow changes within the service area.
(C) The projected 2-hour peak flow shall be the result of collection system
monitoring and/or modeling based on the design storm event for the service area. The design storm event
is generally associated with a 2-year, 24-hour storm event.
(2) Organic loadings. When an existing treatment plant is to be re-rated, expanded, or
upgraded, the design organic loading shall be based on the average daily organic load which the facility is
required to treat during the design life of the facility, based on historical data, plus one standard deviation.
The future organic load may be different from the existing historical base and the engineer shall
characterize the future loading and flow. The engineers report shall serve as the basis for the
development of the design organic loading. The determination shall take into account both dry weather
and wet weather conditions. The historical data base shall conform at a minimum to the protocol outlined
in subparagraphs (A) and (B) of this paragraph. This design organic load is the load which shall be used
to determine the size of any treatment units which are intended to provide treatment of organic wastes.
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(A) In order to utilize the existing data for a re-rating, expansion, or upgrade, the
historical data shall have been taken for a minimum of one year consisting of three samples per week
taken during weekdays. The samples shall, at a minimum, consist of a three-part grab sample taken at
10:00 a.m., noon, and 2:00 p.m. If the system experiences a peak load during another period of the day,
the sampling times may be adjusted as the engineer deems necessary to characterize the treatment plant’s
design organic loading. If a sampling program is recommended by the engineer for a frequency less than
3 times per week or less than a three-part grab sample, then the engineer must show that the proposed
sampling program was representative.
(B) Sampling data shall consist of a minimum of CBOD5 or BOD5, TSS, and
NH3-N unless the engineer justifies a different program because of specific treatment requirements.
(C) The engineering analysis utilizing the minimum sampling period shall consist
of a summary of the monthly data, annual-average monthly load, and standard deviation of the monthly
data. The use of a linear regression or other appropriate statistical method may be utilized for the
prediction of the design organic load when significant data exists.
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§217.34. One Hundred Year Flood Plain Requirements.
(a) 100-Year Flood Plain Shown on Plans. The limits of the 100-year flood plain shall be clearly
indicated on the site plan for the proposed wastewater facility based on the current effective FEMA Flood
Insurance Study (FIS). Flood elevations shall be taken from the appropriate Flood Insurance Rate Map or
FIS profile adjusted to the project’s vertical datum. The limits of the flood plain shall be based on the
superposition of the above- mentioned flood elevations on the most accurate, available topography and
elevations of the proposed site. If the proposed site is adjacent to an “approximate” FEMA 100-year
flood delineation (no flood elevation published), a 100-year flood elevation may be determined by
overlaying the effective FEMA delineation over a United States Geological Survey (USGS) Quadrangle
Map and interpolating a flood elevation. If the flood plain information is not available, the engineer shall
provide a 100-year flood elevation based on the best information available.
(b) 100-Year Flood Plain Shown on Profile. The FEMA 100-year water surface elevation,
determined as indicated in subsection (a) of this section, shall be indicated clearly on the hydraulic profile
of the wastewater facility and located in accordance with the vertical scale of the drawing. When the
proposed plant will occupy less than 1,000 feet of shoreline along the flood plain, a single line coincident
with the elevation of the centerline of the outfall pipe shall be sufficient for 1,000 feet or more of
shoreline, the water surface elevation at both the upstream and downstream limits of any protective
structure for the proposed plant shall be shown on the profile.
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(c) Requirements for Plant Site Protection. Proposed treatment units, which are to be located
within the 100-year flood plain, will not be approved unless satisfactory measures to protect all open
process tanks and electric units are provided as part of the proposed wastewater facility design.
§217.35. Backup Power Requirements.
The executive director may review the engineer’s determination of reliability of the existing
commercial power service. Such determinations shall be based on power outage records obtained from
the appropriate power company and presented to the executive director. When requesting outage records
for submittal to the executive director, the records shall be in writing, bear the signature of an authorized
utility employee, identify the location of the wastewater treatment facilities or off-site lift station(s) being
served, list the total number of outages that have occurred during the past 24 months, and indicate the
duration of each recorded outage. If the executive director judges the power supply unreliable, then an
on-site, automatically-starting generator, which can provide sufficient power to ensure continuous
operation of all critical wastewater treatment system units for a duration equal to the longest power
outage in the power records, shall be provided. Off-site lift stations shall also be provided with an on-site,
automatically-starting generator which provides sufficient power to ensure continuous operation of the lift
station for a duration equivalent to the longest power outage on record for the past 24 months. Exceptions
to the auxiliary power generator requirements for wastewater treatment facilities and outlined in the
following paragraphs, and in the off-site lift stations are detailed in Section 217.64.
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(1) Off-Site Lift Stations. Auxiliary generators will not be required for off-site lift
stations in the following cases:
(A) Reliable electrical service from two separate commercial power companies
and automatic switch over capabilities exist;
(B) Reliable electrical service from two independent feeder lines or substations
of the same electric utility and automatic switch over capabilities exist;
(C) Portable generators or pumps, in combination with collection system storage,
may substitute for on-site generators only in cases where the following criteria exist: the firm capacity of
the lift station is less than 100 gallons per minute; the station includes an autodialer or telemetry system;
operators knowledgeable in acquisition and startup of the portable units are on 24-hour call; the station is
accessible during a 25-year flood event; reasonable assurances exist as to the timely availability and
accessibility of the proper portable equipment; and, the station is equipped with properly designed and
tested quick connection facilities; or
(D) Collection system storage may be utilized in lieu of on-site generators where
calculations included in the engineering design report, show that sufficient volume exists in the lift stations,
upstream gravity sewer lines, and manholes to store the volume of wastewater which would be received
during a peak diurnal event of a duration equal to the longest outage in the power records. If storage is
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utilized in lieu of backup power generators, the design report shall also clearly show that the hydraulic
grade line of the collection system is such that in no case will wastewater be allowed to overflow from the
collection system during a peak diurnal event of a duration equal to the longest outage in the power
records. Spill containment structures are prohibited for use as a means of preventing lift station
discharges during a power outage.
(2) Wastewater Treatment Facilities. The requirements for on-site, automatically-
starting generators may be reduced for wastewater treatment facilities as follows:
(A) If reliable electrical service from two separate commercial power
companies exists which ensures a power supply sufficient to power the entire facility continuously, on-site
generators are not required provided automatic switch over capabilities exist;
(B) If reliable electrical service from two independent feeder lines or substations
of the same electric utility exists which ensures a power supply sufficient to power the entire facility
continuously, on-site generators are not required provided automatic switch over capabilities are in effect;
or
(C) Plant lift stations and collection systems may be utilized to store wastewater
in lieu of on-site generators where calculations included in the engineering design report, show that
sufficient volume exists in the lift stations, upstream gravity sewer lines, and manholes to store the volume
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of wastewater which would be received during a peak diurnal event of a duration equal to the longest
outage in the power records. If storage is utilized in lieu of backup power generators, the design report
shall also clearly show that the hydraulic grade line of the collection system is such that in no case will
wastewater be allowed to bypass the treatment plant during a peak diurnal event of a duration equal to the
longest outage in the power records. The protocol, which shall be followed when upstream storage is
used as a means of ensuring complete treatment of the influent wastewater, is detailed in clauses (i)-(iii)
of this subparagraph.
(i) Storage is prohibited as a substitute for on-site generators if any of
the flow to the treatment plant is gravity flow.
(ii) If the influent storage is between 0 and 2 hours and power outage
records indicate a maximum outage of less than 2 hours, the on-site, automatically- starting generators
need only provide sufficient power to operate all components of the disinfection system.
(iii) If the influent storage is between 2 and 4 hours and the power
outage records indicate an outage between 2 and 4 hours, the on-site, automatically-starting generator
need only supply sufficient power to operate all or components of the disinfection system and return
activated sludge pumps. Auxiliary generators are not required to supply power for return activated sludge
pumps where calculation are included in the engineering design report which show that sufficient volume
exists in the clarifiers for storage of sludge.
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§217.36. Buffer Zone and Design of Odor Abatement Facilities.
All construction of wastewater treatment facilities shall be done in accordance with the buffer
zone restrictions detailed in §309.13 of this title (relating to Unsuitable Site Characteristics). Designs for
odor abatement facilities intended to attain compliance with permit buffer zone requirements shall be
detailed in the engineering design report, and the proposed odor abatement measures shall be summarized
in the summary transmittal letter required by §217.9(c) of this title (relating to Submittal Requirements).
All odor abatement facilities will be considered nonconforming or innovative technologies and will be
reviewed on a case-by-case basis by the executive director.
§217.37. Effluent Reuse.
The engineer shall provide for the utilization of reclaimed water in place of potable water
whenever practical. Typical uses include, but are not limited to: wash down water, water used for the
disinfection system operation, water used for chemical mixing, and water for irrigating the plant grounds.
Reclaimed water shall be taken after disinfection. The system shall provide for screening or filtration,
pumping backup with controls, and a pressure sustaining device such as a hydro-pneumatic tank. This
requirement only applies when Type II water is reclaimed as defined in Chapter 210 of this title (relating
to the Use of Reclaimed Water). If reclaimed water is not used when it is available, a justification for the
use of potable water shall be included in the final engineering design report.
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SUBCHAPTER C : CONVENTIONAL COLLECTION SYSTEMS
§§217.51-217.71
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code as well as the authority to set standards to prevent the
discharge of waste that is injurious to the public health under §26.041 of the Texas Water Code.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.51. Applicability.
This subchapter covers the design, construction, and testing standards for conventional gravity
sewer collection systems, and conventional sewage lift stations, force mains, and reclaimed water
conveyance system.
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§217.52. Edwards Aquifer.
All collection systems to be located over the recharge zone of the Edwards Aquifer shall be
designed and installed in accordance with Chapter 213 of this title (relating to Edwards Aquifer Rules) in
addition to these rules.
§217.53. Pipe Design.
(a) Flow Design Basis. Wastewater collection facilities shall be designed to transport the peak
dry weather flow from the service area, plus infiltration and inflow. The engineer shall prepare
calculations detailing the average dry weather flow, the dry weather flow peaking factor and the
infiltration and inflow. The flow calculations shall include the flow expected in the facilities immediately
upon completion of construction and at the end of its 20-year life.
(b) Gravity Pipe Materials. The choice of sewer pipe shall be based on the characteristics of the
wastewater conveyed, the character of industrial wastes, the possibilities of septic, the exclusion of inflow
and infiltration, the external forces, groundwater, internal pressures, abrasion, and corrosion resistance.
The sewer pipe to be used shall be identified in the plans and technical specifications with its appropriate
ASTM, ANSI or AWWA standard numbers for both quality control (dimensions, tolerances, etc.) and
installation (bedding, backfill, etc.).
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(c) Joints for Gravity Pipe. The materials used and methods to be applied in making joints shall
be included in the technical specifications. Materials used for sewer joints shall have a satisfactory
record of preventing infiltration and root entrance. Rubber gaskets, PVC compression joints, high
compression polyurethane, welded, heat fused, or other types of factory made joints are required. ASTM,
AWWA or other appropriate national reference standards for the joints shall be included in the project
specifications.
(d) Separation Distances Between Wastewater Lines and Water Lines; and Manholes and
Water Lines. Where new wastewater lines or manholes are installed in compliance with the requirements
of this subchapter, they shall be installed no closer than nine feet, in any direction, from any water lines,
measured from the outside of the wastewater line or manhole to the outside of the water line.
Wastewater lines shall be installed in separate trenches from water lines. Where nine feet of separation
cannot be achieved, the project shall comply with the requirements in paragraphs (1)-(4) of this
subsection.
(1) New Wastewater Lines - Parallel Lines. Where new wastewater lines are installed
parallel to an existing water line, the horizontal separation distance shall be no less than four feet and the
vertical separation shall be no less than 2 feet (outside to outside), with the water line above the
wastewater line. The wastewater line shall be constructed of pipe material and joints having a minimum
pressure rating of 150 psi.
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(2) New Wastewater Lines - Wastewater Lines Crossing Water Lines. Where new
wastewater lines are installed crossing an existing waterline, the vertical separation shall be no less than
two feet or more below a water line, at a crossing angle between 75 degrees and 90 degrees, with pipe
segment lengths of 18 feet or greater. With these types of installations, one segment of the wastewater
pipe shall be centered under the potable water line such that the joints of the wastewater pipe are
equidistant from the center line of the potable water line. Whenever possible, the crossing shall be
centered between the joints of the potable water line. All wastewater pipe within a distance of 9 feet
from the water line, in every direction as measured perpendicularly from any point on the water pipe to
the wastewater pipe, shall have either a pressure rating for both joints and pipe of 150 psi.
(3) New Wastewater Lines - Other Crossings. Any wastewater line crossing which is
not installed two feet or more below the water line, installed at a crossing angle of less than 75 degrees, or
which uses pipe segment lengths less than 18 feet in length, shall be installed with the same requirements
as those detailed in paragraph (2) of this subsection, with the addition that the minimum distance between
the outside of any wastewater line and the outside of any water line shall be 6 inches and that all portions
of wastewater pipe, which are not rated at a minimum pressure of 150 psi for both joints and pipe, which
are within 9 feet of the water line, as measured perpendicularly from any point on the water pipe to the
wastewater pipe, shall be embedded in cement stabilized sand. Where cement stabilized sand is used, the
sand shall have a minimum of 10 percent cement per cubic yard of cement stabilized sand mixture, based
on loose dry weight volume (at least 2.5 bags of cement per cubic yard of mixture. The cement stabilized
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sand bedding shall be a minimum of 6 inches above and one quarter of the pipe diameter on either side
and below the sewer pipe.
(4) Manholes and Water Lines. If a manhole is to be placed at a distance of less than 9
feet from a water line, the water line shall be encased in a new encasement, a minimum of 18 feet long,
with a pressure rating of at least 150 psi with a nominal diameter of at least two sizes larger than the
existing or proposed water line. The space around the carrier pipe shall be supported at 5 foot intervals
with spacers or be filled to the spring line with washed sand. The encasement pipe shall be centered on
the crossing and both ends sealed with cement grout or manufactured seal.
(e) Laterals and taps. Lateral and taps on all new installations shall be made with a
manufactured fitting that will limit infiltration, prevent protruding service lines, and protect the mechanical
and structural integrity of the sewer system.
(f) Bore/Tunnel For Crossings. Supports for carrier pipe through casings shall be spaced and
designed to ensure that adequate grade, slope, and structural integrity is maintained.
(g) Corrosion Potential. For all installations, if a pipe as a whole or an integral structural
component of the pipe will deteriorate when subjected to corrosive internal conditions, a corrosive
resistant liner shall be installed at the pipe manufacturing facility unless the final engineering design report,
including calculations and data submitted by the engineer, demonstrates that the design and operational
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characteristics of the system will maintain the structural integrity of the system during the minimum 50
year design life cycle. If the corrosion analysis indicates that corrosion will reduce the facility life to less
than 50 years, then appropriate linings shall be incorporated into the design of the facility.
(h) Odor Control. The designer, based upon the hydrogen sulfide generation potential of the
collection system facility, shall determine if odor control measures are necessary to prevent the
wastewater collection system from becoming a nuisance to the public adjacent to the collection facility.
The odor potential shall be determined for flows immediately following construction, at the end of its 50
year life, and for periods between these points, as appropriate.
(i) Active Geologic Faults. For systems to be located in areas of known active geologic faults,
the engineer shall locate any faults within the area of the collection system, and the system shall be laid
out to minimize the number of sewers crossing faults. Where crossings are unavoidable, the engineering
report shall specify design features to protect the integrity of the sewer. Consideration shall be given to
joints providing maximum deflection and to providing manholes on each side of the fault so that a portable
pump may be used in the event of sewer failures. Service connections within 50 feet of an active fault
shall be prohibited.
(j) Capacity Analysis. Sewer lines shall be designed for the estimated future population to be
served plus adequate allowance for institutional and commercial flows. The peak flow of domestic
sewage, peak flow of waste from industrial plants, and maximum infiltration rates shall be considered in
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determining the hydraulic capacity of sanitary sewers. Systems shall be designed to preclude surcharge
at the expected peak flow. All gravity pipes shall have a minimum diameter of 6-inches. combined
sewers are prohibited. connection of roof, street, or other types of drains to sanitary sewer systems is
prohibited.
(1) Existing Systems. When available, the design of extensions to sanitary sewers shall
be based on the data from the existing system. In the absence of existing data, the design shall be based
on data from similar systems or as described in paragraph (2) of this subsection.
(2) New Systems. New sewers shall be sized using an appropriate engineering analysis
of existing and future flow data. The review authority shall have the authority to determine the reliability
and appropriateness of the data utilized for sizing the system. In the absence of local, reliable flow data
and engineering analysis, new sewer systems shall be designed on the basis of an estimated daily sewage
flow contribution as shown in the Table B.1 in §217.32 of this title (relating to Design of New Systems
Organic Loadings and Flows). Minor sewers shall be designed such that when flowing full they will
transport wastewater at a rate approximately four times the system design daily average flow. Minor
Sewers shall be defined as all sewer lines 8" in diameter and less. All other sewer lines shall be designed
to convey the maximum possible flow contributed from any connected minor sewers.
(k) Structural Analysis. The collection system design shall provide a minimum structural life
cycle of 50 years. The owner of the collection system shall provide inspection under the direction of a
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Texas Licensed Professional Engineer during the construction and testing phases of the project. A
flexible pipe is defined as one that will deflect at least 2 percent without structural distress. Materials that
do not meet this criteria are considered to be rigid. Pipe designs shall ensure that the specified pipes are
appropriate for the proposed installations. The flexible pipe design analysis detailed in paragraph (1) of
this subsection shall be performed for flexible pipe installations, and the rigid pipe design analysis detailed
in paragraph (2) of this subsection shall be performed for rigid pipe installations. Open trench designs,
using flexible pipe with a pipe stiffness of 46 psi or greater, a burial depth of 17 feet or less, a pipe
diameter of 12-inches or less, a modules of soil reaction for the in-situ soil of 200 psi or greater, no effects
on the pipe due to live loads, a unit weight of soil of 120 pounds per cubic foot or less, and a pipe trench
width of 36 inches or greater are not required to perform the structural calculations in paragraph 1,
provided that the pipe is installed and tested in accordance with all other requirements of this subchapter.
Flexible pipe designs using pipes with pipe stiffness less than 46 psi or not meeting these conditions shall
complete all the structural design calculations detailed in paragraph (1) of this subsection.
(1) Flexible Pipe. Live load calculations; allowable buckling pressure determinations;
prism load calculations; wall crushing determinations; strain prediction calculations; and calculations which
quantify long term pipe deflection shall be included in the final engineering design report. The final
engineering design report shall include all information pertinent to the determination of an adequate design
including, but not limited to, the method of determining modules of soil reaction for bedding material; the
method of determining modules of soil reaction for in-situ material; pipe diameter and material with
reference to appropriate standards; modules of elasticity, tensile strength, pipe stiffness, or ring stiffness
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constant converted to pipe stiffness as described below; Leonhardt's zeta factor; trench width; depth of
cover; water table elevation; and unit weight of soil. In all cases, the design procedure shall dictate the
minimum pipe stiffness. For direct bury installations, a minimum stiffness requirement shall be specified
by the engineer to ensure ease of handling, transportation, and construction. Where appropriate, pipe
stiffness shall be related to Ring Stiffness Constant (RSC) by the following equation: (Figure 1:
§217.53(j)(1)
PS’C(RSC( (8.337/D) Equation 1.c
PS = Pipe Stiffness, psi;
C = Conversion Factor, (0.80);
RSC = Ring Stiffness Constant; and,
D = Mean Pipe Diameter, in.
(2) Rigid Pipe. The final engineering design report shall include a structural analysis of
the pipe installation and shall include any details necessary to verify that the structural strength of the rigid
pipe is sufficient to withstand the stresses which the pipe is expected to experience. For rigid conduits,
the minimum strengths for the given class shall be noted in the appropriate standard for the pipe material.
A rigid pipe is defined as one that will experience structural distress at a deflection of 2% or greater.
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(l) Minimum/Maximum Slopes. All sewers shall be designed and constructed with slopes
sufficient to give a velocity when flowing full of not less than 2.0 feet per second. The grades shown in
Table C.1 are based on Manning's formula with an assumed "n factor" of 0.013 and constitute minimum
acceptable slopes. The minimum acceptable "n" for design and construction shall be 0.013. The "n" used
takes into consideration the slime, grit and grease layers that will affect hydraulics or hinder flow as the
pipe matures. Where velocities greater than 10 feet per second will occur when the pipe is flowing full,
based on Manning’s formula and an n value of 0.013, special provisions shall be made to protect against
pipe and bedding displacement. Figure 2: §217.53 (k)
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Table C.1 - Minimum and Maximum Pipe Slopes
Size of Pipe (inches) Minimum Slope (%) Maximum Slope (%)
6 0.50 12.35
8 0.33 8.40
10 0.25 6.23
12 0.20 4.88
15 0.15 3.62
18 0.11 2.83
21 0.09 2.30
24 0.08 1.93
27 0.06 1.65
30 0.055 1.43
33 0.05 1.26
36 0.045 1.12
39 0.04 1.01
>39 * *
* For lines larger than 39 inches in diameter, the slope shall be determined by Manning's formula (as shown below) to maintain a minimum velocity greater than 2.0 feet per second when flowing full and a maximum velocity less than 10 feet per second when flowing full.
V’ (1.49/n)( (Rh 0.67 )( ( S) Equation 2.c
V = velocity (ft/sec)n = Manning's roughness coefficient (0.013)Rh = hydraulic radius (ft)S = slope (ft/ft)
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(m) Alignment. Gravity sewers shall be laid in straight alignment with uniform grade between
manholes when possible. Deviations from straight alignment shall be justified by complying with the
requirements of this section. Deviations from uniform grade (i.e., grade breaks or vertical curves)
without manholes in open cut construction is prohibited.
(1) Construction methods which utilize flexure of the pipe joint are prohibited. The
engineer shall provide the calculations for horizontal pipe curvature in the final engineering design report
and detail the proposed curvature on the plans or shall indicate curvature of the pipe on the plans. The
maximum allowable joint deflection shall be the lesser of the following three alternatives:
(A) equal to 5E;
(B) 80% of the manufacturer's recommended maximum deflection; or,
(C) 80% of the appropriate ASTM, AWWA, ANSI or nationally-established
standard for joint deflection.
(2) The maximum allowable manhole spacing for sewers with horizontal curvature shall
be 300 feet. A manhole shall be located at the P.C. and P.T. of the curve.
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(m) Inverted Siphons/Sag Pipes. Sag pipes shall have two or more barrels, a minimum pipe
diameter of six inches, and shall be provided with necessary appurtenances for convenient flushing and
maintenance. The manholes shall have adequate clearances for rodding. Sufficient head shall be
provided and pipe sizes selected to assure velocities of at least three feet per second at initial and design
flows. The inlet and outlet details shall be arranged so that the normal flow is diverted to one barrel.
Provisions shall be made such that any barrel may be taken out of service for cleaning. Provisions shall
be made to allow cleaning across each bend with equipment available to the entity in charge of operation
and maintenance of the facility. Sag pipes design shall minimize nuisance odors.
(n) Bridged Sections. Pipe with restrained joints or monolithic pipe shall be required between
manholes on each end of bridged sections. Bridged sections shall be designed to withstand the hydraulic
forces applied by the occurrence of a 100-year flood including buoyancy. Pipe material shall also be
capable of withstanding impacts from debris. Bank stabilization shall be provided to prevent erosion of
bank sections. Bridge supports shall be spaced and designed to ensure that adequate grade, slope, and
structural integrity are maintained.
§217.54. Pipe Bedding.
(a) Bedding Material. Bedding Classes A, B, or C, as described in ASTM C 12 (ANSI A
106.2), Water Environment Federation (WEF) Manual of Practice (MOP) No. 9, or American Society of
Civil Engineers (ASCE) MOP 37 shall be used for all rigid pipes, provided that the proper strength pipe is
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used with the specified bedding to support the anticipated load(s). Embedment materials Classes IA, IB,
II, or III, as described in ASTM D-2321 (ANSI K65.171), shall be used for all flexible pipes. Regardless
of which bedding class is used, the pipe strength shall be sufficient to support the anticipated load when
used with the specified pipe bedding as required by §217.53(i) of this title (relating to Pipe Design).
Debris, large clods or stones greater than six inches in diameter, organic matter, or other unstable
materials shall not be used as hunching or initial backfill. All backfill shall be placed in such a manner as
not to disturb the alignment of the pipe. Where trenching encounters extensive fracture or fault zones,
caves, or solutional modification to the rock strata, construction shall be halted and an engineer shall
provide direction to accommodate site conditions.
(b) Bedding Compaction. Compaction of bedding envelope shall be in accordance with pipe
manufacturers recommendations and shall be sufficient to provide the modules of soil reaction for the
bedding material necessary to ensure the pipe’s structural integrity as required by §217.53(i) of this title.
The placement of the backfill above the pipe shall not affect the structural integrity of the pipe.
(c) Envelope Size. A minimum clearance of 6 inches below and on each side of the bell of all
pipes to the trench walls and floor shall be provided. The bedding or embedment material class used for
haunching and initial backfill shall be installed to a minimum depth of 12 inches above the crown of the
pipe.
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(d) Trench Width. The width of the trench shall be ample to allow the pipe to be laid and jointed
properly and to allow the backfill to be placed and compacted as needed. As used herein, a trench shall
be defined as that open cut portion of the excavation up to one foot above the pipe. The engineer shall
specify the maximum and minimum trench width needed for safety and the pipe’s structural integrity.
The width of the trench shall be sufficient to ensure working room to properly and safely place and
compact hunching materials. The space between the pipe and the trench wall shall be wider than the
compaction equipment used in the pipe zone.
Figure 1: §217.54(d)
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§217.55. Manholes and Related Structures.
Manholes shall be placed at all points of change in alignment, grade or size of sewer, at the
intersection of all sewers, and at the end of all sewer lines that may be extended at a future date.
Manholes placed at the end of the sewers that may be extended in the future shall include pipe stub outs
with plugs. Clean-outs with watertight plugs may be installed in lieu of manholes at the end of sewers
which are not anticipated to be extended. Cleanout installations shall pass all applicable testing
requirements outlined for gravity collection lines in this subchapter.
(1) Types (Materials). Manholes shall be monolithic cast-in-place concrete, fiberglass,
precast concrete, HDPE or of equivalent construction. Brick manholes are prohibited. The use of brick
to adjust manhole covers to grade is prohibited. All cast-in-place manholes shall be adequately designed
for structural integrity.
(2) Spacing. The maximum required manhole spacing for sewers with straight alignment
and uniform grades are in the Table C.2. Areas subject to flooding require special consideration to
minimize inflow. Tunnels are exempt from manhole spacing requirements due to construction constraints.
Tunnels are required to meet any venting requirements. Figure 1: §217.55(2)
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Table C.2 - Maximum Manhole Spacings
Pipe Diameter (inches) Maximum Manhole Spacing (feet)
6-15 500
18-30 800
36-48 1000
54 or larger 2000
(3) Diameter/Size. Manholes shall be of sufficient inside diameters to allow personnel to
work within them and to allow proper joining of the sewer pipes in the manhole wall. The minimum inside
diameter of manholes shall be 48 inches.
(4) Covers/Inlets/Base.
(A) Manhole Covers. Manhole covers of nominal 30 inch or larger diameter are
required for all sewer manholes where personnel entry is anticipated. Manholes located within the 100
year flood plain shall have gasketed and bolted covers, or have another means of preventing inflow.
Impervious material shall be utilized for manhole cover construction.
(B) Manhole Inverts. The bottom of the manhole shall be provided with a "U"
shaped channel that is a smooth continuation of the inlet and outlet pipes. For manholes connected to
pipes less than 15 inches in diameter, the channel depth shall be at least half the largest pipe diameter.
For manholes connected to pipes 15 to 24 inches in diameter, the channel depth shall be at least three
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fourths the largest pipe diameter. For manholes connected to pipes greater than 24 inches in diameter, the
channel depth shall be at least equal to the largest pipe diameter. In manholes with pipes of different
sizes, the tops of the pipes shall be placed at the same elevation and flow channels in the invert sloped on
an even slope from pipe to pipe. The bench provided above the channel shall be sloped at a minimum of
0.5 inch per foot. Where sewer lines enter the manhole higher than 24 inches above the manhole invert,
the invert shall be filleted to prevent solids deposition. A drop pipe shall be provided for a sewer entering
a manhole more than 30 inches above the invert. If the drop is inside the manhole, a minimum of 48
inches of clear space shall be maintained and the drop shall be permanently affixed to the wall of the
manhole.
(5) Manhole Steps. The inclusion of manhole steps in manholes is prohibited.
(6) Connections. Watertight, size-on-size resilient connectors allowing for differential
settlement shall be used to connect pipe to manholes. Pipe to manhole connectors shall conform to
ASTM C-923.
(7) Venting. Where gasketed manhole covers are required for more than three
manholes in sequence, an alternate means of venting shall be provided at less than 1,500 foot intervals.
Vents shall be designed to minimize inflow. Vents shall be above the 100-year flood elevation.
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(8) Cleanouts. Cleanouts shall be required to be the same size as the main and shall be
restricted to lengths of pipe less than 150'.
§217.56. Trenchless Design for Collection Systems.
Pipe installations using trenchless design shall be considered nonconforming technology and shall
be subject to review under the requirements of §217.10(2) of this title (relating to Types of Approvals).
Structural design and installation details of trenchless designs shall be approved by the reviewing authority
prior to construction.
§217.57. Testing Requirements for Installed Gravity Collection Lines.
An infiltration, exfiltration, or low-pressure air test shall be specified. Copies of all test results
shall be made available to the review authority upon request. Tests shall conform to the following
requirements:
(1) Low Pressure Air Test. The procedure for the low pressure air test shall conform to
the procedures described in ASTM C-828, ASTM C-924, ASTM F-1417, or other appropriate
procedures, except for testing times. The test times shall be as outlined in this section. For sections of
pipe less than 36-inch average inside diameter, the following procedure shall apply unless the pipe is to be
joint tested. The pipe shall be pressurized to 3.5 psi greater than the pressure exerted by groundwater
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above the pipe. Once the pressure is stabilized, the minimum time allowable for the pressure to drop from
3.5 pounds per square inch gauge to 2.5 pounds per square inch gauge shall be computed from the
following equation: Figure 1:§217.57(1)
T’ (0.085(D(K)/Q Equation 3.c
T = time for pressure to drop 1.0 pound per square inch gauge in seconds
K = 0.000419×D×L, but not less than 1.0
D = average inside pipe diameter in inches
L = length of line of same pipe size being tested, in feet
Q = rate of loss, 0.0015 cubic feet per minute per square foot internal surface shall be
used
(A) Since a K value of less than 1.0 shall not be used, there are minimum testing
times for each pipe diameter as shown in Table C.3. Figure 2: §217.57(1)(A)
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Table C.3 - Minimum Testing Times for Low-Pressure Air Test
Pipe Diameter (inches) Minimum Time (seconds) Length for Minimum Time
(feet)
Time for Longer Length
(seconds)
6 340 398 0.855(L)
8 454 298 1.520(L)
10 567 239 2.374(L)
12 680 199 3.419(L)
15 850 159 5.342(L)
18 1020 133 7.693(L)
21 1190 114 10.471(L)
24 1360 100 13.676(L)
27 1530 88 17.309(L)
30 1700 80 21.369(L)
33 1870 72 25.856(L)
(B) The test may be stopped if no pressure loss has occurred during the first
25% of the calculated testing time. If any pressure loss or leakage has occurred during the first 25% of
the testing period, then the test shall continue for the entire test duration, as outlined above, or until failure.
Lines with a 27-inch average inside diameter and larger may be air tested at each joint. Pipe greater than
36-inch diameter shall be tested for leakage at each joint. If the joint test is used, a visual inspection of
the joint shall be performed immediately after testing. The pipe shall be pressurized to 3.5 psi greater than
the pressure exerted by groundwater above the pipe. Once the pressure has stabilized, the minimum time
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allowable for the pressure to drop from 3.5 pounds per square inch gauge to 2.5 pounds per square inch
gauge shall be 10 seconds.
(2) Infiltration/Exfiltration Test. The total exfiltration, as determined by a hydrostatic
head test, shall not exceed 50 gallons per inch diameter per mile of pipe per 24 hours at a minimum test
head of two feet above the crown of the pipe at the upstream manhole. Following the exfiltration test, the
pipe shall be drained and shall be left empty for a period of 24 hours, upon which time the amount of
infiltration into the pipe shall be measured. The total infiltration for this period of time shall not exceed 50
gallons per inch diameter per mile of pipe. When pipes are installed below the groundwater level, an
infiltration test shall be used in lieu of the exfiltration test. The total infiltration, as determined by a
hydrostatic head test, shall not exceed 50 gallons per inch diameter per mile of pipe per 24 hours at a
minimum test head of two feet above the crown of the pipe at the upstream manhole, or at least two feet
above existing groundwater level, whichever is greater. For construction within the 25 year flood plain,
the infiltration or exfiltration shall not exceed 10 gallons per inch diameter per mile of pipe per 24 hours at
the same minimum test head. If the quantity of infiltration or exfiltration exceeds the maximum quantity
specified, remedial action shall be undertaken in order to reduce the infiltration or exfiltration to an amount
within the limits specified. Following remediation action, the line shall be retested.
(3) Deflection Testing. Deflection tests shall be performed on all flexible pipes. For
pipelines with inside diameters less than 27 inches, a rigid mandrel shall be used to measure deflection.
For pipelines with an inside diameter 27 inches and greater, other methods may be used to test for vertical
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deflections. Other methods shall provide a precision of ± two tenths of one percent (0.2 %) deflection.
The test shall be conducted after the final backfill has been in place at least 30 days. No pipe shall
exceed a deflection of five percent. If a pipe section fails to pass the deflection test, the problem shall be
corrected, and a second test shall be conducted after the final backfill has been in place an additional 30
days. The tests shall be performed without mechanical pulling devices. The engineer shall recognize that
this test is a maximum deflection criterion for all pipes, and a deflection of less than five percent may be
more appropriate for specific types and sizes of pipe. Upon completion of construction, the engineer or
other Texas Licensed Professional Engineer appointed by the owner shall certify, to the Review
Authority, that the entire installation has passed the deflection test. This certification may be made in
conjunction with the notice of completion required in §217.13 of this title (relating to Completion
Notification). This certification shall be provided for the Review Authority to consider the requirements
of the approval to have been met.
(A) Mandrel Sizing. The rigid mandrel shall have an outside diameter (O.D.) not
less than 95% of the base inside diameter (I.D.) or average inside diameter of the pipe, as specified in the
appropriate ASTM, AWWA, UNI-BELL, or ANSI Standard, including any appendix. If a mandrel sizing
diameter is not specified in the appropriate standard, the mandrel shall have an O.D. equal to 95% of the
I.D. of the pipe. In this case, the I.D. of the pipe, for the purpose of determining the O.D. of the mandrel,
shall be the average outside diameter minus two minimum wall thicknesses for O.D. controlled pipe and
the average inside diameter for I.D. controlled pipe. All dimensions shall be per appropriate standard.
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(B) Mandrel Design. The rigid mandrel shall be constructed of a metal or a rigid
plastic material that can withstand 200 psi without being deformed. The mandrel shall have nine or more
"runners" or "legs," and the total number of legs shall be an odd number. The barrel section of the
mandrel shall have a length of at least 75% of the inside diameter of the pipe. A proving ring shall be
provided and used for each size mandrel in use.
(C) Method Options. Adjustable or flexible mandrels are prohibited. A television
inspection is not a substitute for the deflection test. A deflectometer may be approved for use on a case-
by-case basis. Mandrels with removable legs or runners may be approved for use on a case-by-case
basis.
§217.59. Testing Requirements for Manholes.
Manholes shall be tested for leakage separately and independently of the wastewater lines by
hydrostatic exfiltration testing, vacuum testing, or other methods acceptable to the Executive Director or
the designated Executive Director or the designated Reveiw Authority. The manhole shall be tested after
assembly and after backfilling. If a manhole fails a leakage test, the manhole shall be repaired and
retested until it passes the test.
(1) Hydrostatic Testing. The maximum leakage for hydrostatic testing shall be 0.025
gallons per foot diameter per foot of manhole depth per hour. Alternative test methods shall ensure
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compliance with the above-allowable leakage. Hydrostatic exfiltration testing shall be performed as
follows: all wastewater lines coming into the manhole shall be sealed with an internal pipe plug, then the
manhole shall be filled with water, and maintained full for at least one hour. For concrete manholes a
wetting period of 24 hours may be used prior to testing in order to allow saturation of the concrete. If the
manhole fails the hydrostatic test, the manhole shall be repaired and retested until it passes the test.
(2) Vacuum Testing. All lift holes and exterior joints shall be plugged with a non-shrink
grout. No grout shall be placed in horizontal joints prior to testing. All pipes entering the manhole shall be
plugged. Stubouts, manhole boots, and pipe plugs shall be secured to prevent movement while the vacuum
is drawn. A minimum 60-inch/lb torque wrench shall be used to tighten the external clamps that secure
the test cover to the top of the manhole. The test head shall be placed at the inside of the top of the cone
section, and the seal inflated in accordance with the manufacturer’s recommendations. A vacuum of 10
inches of mercury shall be drawn, and the vacuum pump shut off. With all valves closed, the time for the
vacuum to drop to 9 inches of mercury shall not be less than 2 minutes. If vacuum tests are used in lieu
of hydrostatic tests, the test shall be done both before and after backfilling of the manhole has occurred.
If the manhole fails a test, necessary repairs shall be made with a non-shrink grout while the vacuum is
being drawn. The test shall be repeated. If the vacuum test is failed twice, the manhole shall be repaired,
and a hydrostatic test shall be performed in accordance with paragraph (1) of this section.
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§217.60. Lift Station Site Selection.
(a) Site access. The lift station shall have an access road located in a dedicated right-of-way or
a permanent easement. The road surface shall have a minimum width of 12 feet and shall be constructed
for access in all weather conditions. The road surface shall be above the water level caused by a 25-year
storm event.
(b) Security. The lift station, including mechanical and electrical equipment, shall be protected
from access by any unauthorized person. The lift station shall be enclosed within an intruder resistant
fence or located entirely within a lockable structure. An intruder resistant fence shall consist of a
minimum of a chain link fence 6 feet in height with a 1-foot section above consisting of 3 strands of
barbed wire.
(c) Flood Protection. The lift station including all electrical and mechanical equipment shall be
protected from a flood event on a 100-year frequency including wave action, and be fully operational
during such event.
(d) Odor Control. Lift stations shall be designed in a manner to minimize odor potential.
Incoming wet well gravity pipes shall be located to reduce turbulence. Retention times in the wet well
shall be minimized.
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§217.61. Lift Station Wet Well/Dry Well Design Considerations.
(a) Pump Controls. All lift stations shall operate automatically based on the water level in the
wet well. Wet well level mechanisms shall be located so that they are unaffected by currents, rags,
grease, or other floating materials. All level mechanisms shall be fully accessible without entering the wet
well. Where bubbler systems are utilized for wet well control, dual air supply, and controls are required.
(b) Flood Protection. All electrical equipment shall be protected during a 100-year flood event
and be protected from potential flooding from the wet well. Motor control centers shall be mounted on a
4-inch tall housekeeping pad. All electrical equipment and connections in wet wells and dry wells shall
be explosion proof unless continuous ventilation is provided.
(c) Wet Wells. Wet wells and dry wells, including their structure, shall be separated by a
watertight and gas tight wall. All wall penetrations shall be gas tight. Equipment requiring regular or
routine inspection and maintenance shall not be located in the wet well, unless maintenance can be made
without entering the wet well. All gravity lines discharging to the wet well shall be located where the
invert elevation is above the liquid level of the pumps "on" setting. Gate valves and check valves shall not
be located in the wet well. Gate valves and check valves shall be located in a valve vault next to the wet
well. Based on peak flow, pump cycle time shall not be less than the those in Table C.4. Figure 1:
§217.61 (c)
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Table C.4 - Minimum Pump Cycle Times
Pump Horsepower Minimum Cycle Times (minutes)
less then 50 6
50 - 100 10
Over 100 15
Minimum Wet Well Volume shall be based on the following formula:
V’ (T(Q)/(4(7.48) Equation 4.c
V = Volume (ft3)
Q = Pump Capacity (GPM)
T = Cycle Time (Minutes)
7.48 = conversion factor in gallons/cubic foot
(d) Dry well access. Access shall be provided to underground dry wells. Stairways shall have
non-slip steps and conform to OSHA regulations with respect to rise and run. Where ladders are utilized
in lieu of stairways, ladders shall conform to OSHA requirements.
(e) Lift Station Ventilation.
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(1) Passive Ventilation for Wet Wells. Passive ventilation such as gooseneck type or
turbine type shall be screened to prevent the entry of birds or insects to the wet well. If passive
ventilation is provided for the wet well, all mechanical and electrical equipment in the wet well shall be of
explosion-proof construction. The passive ventilation shall be sized to vent at a rate equal to the maximum
pumping rate of the station and not exceed 600 fpm through the vent pipe. The minimum air vent size
shall be 4-inch diameter. Vent outlets shall be at least 1 foot above the 100-year flood elevation.
(2) Mechanical Ventilation in Lift Stations.
(A) Dry Wells. Mechanical ventilation shall be provided for all dry wells.
Ventilation equipment under continuous operations shall have a minimum capacity of six air changes per
hour. Ventilation equipment under intermittent duty shall have a minimum capacity of thirty air changes
per hour and be interlocked with the station's lighting system and a gas detection system. The gas
detection system shall monitor, at a minimum, oxygen deficiency, lower flammable limit (LFL), and
hydrogen sulfide concentration.
(B) Wet Wells. If explosion proof mechanical and electrical equipment is not
provided throughout the wet well, continuous mechanical ventilation shall be used to ventilate the wet
well. The ventilation equipment shall be sized for 12 air changes per hour and constructed of corrosion
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resistant material. In residential areas, consideration shall be given to reducing potential odors from the
ventilated wet well.
(f) Wet Well Slopes. The wet well floors shall have a minimum of 10 percent slope to the pump
intakes and have a smooth finish. There shall be no wet well projections which will allow deposition of
solids under normal operating conditions. Anti-vortex baffling shall be included on all lift stations with
greater than 5 MGD firm pumping capacity.
(g) Hoisting Equipment. Hoisting equipment or an access by hoisting equipment for removal of
pumps, motors, valves, etc., shall be incorporated into all lift station designs.
(h) Dry Well/Valve Vault Drains. Floor drains from valve vaults to wet wells shall be designed
to prevent gas from entering the valve vault. Such designs shall include flap valves, "P" traps, submerged
outlets, or a combination of these devices.
(i) Dry Well Sump Pumps.
(1) Pumps. Dual sump pumps, each with a minimum capacity of 1000 gallons per hour
and capable of handling liquid generated during peak operations, shall be provided in all dry wells. Pumps
shall have submersible motors. All wiring to the sump pumps shall be water tight. Dry well floors shall be
sloped toward a sump sized for each pump for proper drainage. The minimum sump depth shall be 6
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inches and shall be designed to prevent standing water on the dry well floor under normal operation.
Sump pumps shall operate automatically by use of a float switch or other level device.
(2) Piping. Sump pumps shall have separate piping which discharges above the
maximum liquid level of the wet well. The piping shall be a minimum of 1½ inches in diameter. Each
sump pump discharge pipe shall include two check valves in series.
§217.62. Pumps for Lift Stations.
(a) General Requirements. All raw sewage pumps shall be of a non-clog design, capable of
passing an incompressible sphere of 3-inches in diameter or greater, and shall have no less than 4-inch
diameter suction and discharge openings. Inspection and cleanout plates, located both on suction and
discharge sides of each pumping unit, are required for all non-submersible pumps to facilitate locating and
removing blockage causing materials unless the pump design accommodates easy removal of the rotation
elements. All pumps shall be securely supported to prevent movement or vibration during operation. For
submersible pumps, rail-type pump support systems, incorporating manufacturer approved mechanisms
designed to allow personnel to remove and replace any single pump without first entering or dewatering
the wet well, shall be provided. Submersible pump rails and lifting chains shall be constructed of Series
300 stainless steel.
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(b) Lift stations designed for a peak flow of less than 120 gallons per minute shall be of
submersible design using grinder pumps.
(c) Lift Station Pumping Capacity. The firm pumping capacity of all lift stations shall be such
that the expected peak flow can be pumped to its desired destination. Firm pumping capacity is defined
as total station, maximum pumping capacity with the largest pumping unit out of service.
(d) Pump Head Calculations. The selection of pumps shall be based upon analysis of the system
head and pump capacity curves which determine the pumping capacities alone and with other pumps as
the total dynamic-head increases due to additional flows pumped through the force main. Piping head loss
shall be calculated in accordance with the Hydraulic Institute standards pertaining to head losses through
piping, valves, and fittings. The selected C factor used in calculation of friction head losses shall be based
on the pipe material selected. (Generally between 100 and 140). For lift stations with more than 2 pumps,
force mains in excess of one half mile, or firm pumping capacity of 100 gpm or greater, system curves
shall be provided for both the normal and peak operating conditions at C values for new and old pipe.
(e) Flow Control. Lift stations or transfer pumping stations located at wastewater treatment
systems, or those lift stations discharging directly to a wastewater treatment system, shall have a peak
pump capacity no greater than the peak design flow of the wastewater treatment system unless flow
splitting or equalization is provided. For wastewater treatment systems where the peak two hour flow is
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greater than 300,000 gallon per day, three or more pumps shall be provided, unless duplex automatically
controlled variable capacity pumps are provided.
(f) Self Priming Pumps. Self priming pumps shall be capable of priming at the design pump "on"
wet well level without reliance upon a separate priming system on the pump, an internal flap valve, or any
external means for priming. Suction pipe velocity shall be between 3 and 7 feet per second (fps), and
each pump shall have its own suction pipe. Each self priming pump shall include a means of venting air
back into the wet well during priming.
(g) Vacuum Priming Pumps. Vacuum primed pumps shall be capable of priming at the design
pump “on” wet well level by utilizing a separate positive priming system with a dedicated vacuum pump
for each main sewage pump. Suction pipe velocity shall be between 3 and 7 fps. Each pump shall have
its own suction pipe.
(h) Vertical Positioning of Pumps. All raw sewage pumps, other than submersible pumps with
"no suction" piping, vacuum primed pumps, or self-priming units capable of satisfactory operation under
any negative suction heads anticipated for the lift station under consideration, shall be positioned such that
the pumps always experience, during their normal on-off cycling, a positive static suction head.
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(i) Individual Grinder Pumps. Grinder pump stations, serving only one residential or commercial
structure which is privately owned, maintained, and operated, shall be designed in accordance with all
local codes, ordinances, and other local requirements and are not subject to the rules of this Chapter.
§217.63. Lift Station Piping.
(a) Horizontal Pump Suctions. Each pump shall have a separate suction pipe. Eccentric reducers
shall be used on suction pipes in lieu of a concentric reducer. Pipes in wet wells shall be equipped with a
turn-down type flared intake.
(b) Valves. A check valve shall be installed on the discharge side of each pump followed by a
full-closing isolation valve on each pump. Check valves shall be swing type with an external lever. If the
full-closing valve is other than a rising stem gate valve, the valve shall include a position indicator to show
its open or closed position. Rubber ball check valves may be used for grinder pump installations only, in
lieu of swing type check valves. Butterfly valves, tilting disc check valves, or other valves utilizing a tilting
disc in the flow line shall not be allowed.
(c) Piping. Lift station piping shall have flanged or flexible connections to allow for removal of
pumps and valves without interruption of the lift station operations. Wall penetrations shall be designed to
allow for pipe flexure while excluding exfiltration or infiltration. Pipe suction velocities shall be between 3
and 7 feet per second.
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§217.64. Emergency Provisions for Lift Stations.
Lift Stations shall be designed to prevent upstream overflows or by-passing of surcharge of raw
sewage. An audio-visual alarm system (red flashing light and horn) shall be provided for all lift stations.
All alarm conditions shall be transmitted, through use of an auto-dialer system or telemetering system, to a
location(s) where 24-hour assistance is available. The alarm system shall be activated in case of power
outage, pump failure, or a specified high wet well water level. In addition to the alarms and telemetering
requirements, all lift stations constructed to pump raw sewage, located at either the wastewater treatment
system or in the collection system, shall be provided with service reliability based on the options detailed in
paragraphs (1)-(5) of this section.
(1) Retention Capacity. The retention capacity in the lift station's wet well and incoming
gravity sewer lines shall be designed to insure that no discharges of untreated wastewater will occur at
the station or any point upstream for a period of time equal to the longest electrical outage recorded
during the past 24 months. If no records are available, the designer shall use 120 minutes to calculate
required retention capacity. A minimum of a 20-minute retention period shall be used even when power
company records indicate a shorter period of outage. Power outage records shall be on the utility
company letterhead, bear the signature of a utility representative, identify the location of the lift station, list
the total number of outages that have occurred in the past 24 months, and indicate the duration of each
power outage. For calculation purposes, the start of the outage period shall begin at the wet well
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elevation at which the last normally operating pump, excluding the standby pump, has just begun to
operate.
(2) Dual-Fed Electrical Power. The lift station may meet the emergency power
requirement by arranging for the facility to receive electrical service through either two separate electrical
distribution circuits or from separate power companies which have a fully automatic switch over
capability designed to assure continuous service. The two distributions lines shall be physically separated,
not carried on the same pole, and obtain their power from different substations. If separate distribution
circuits originate from the same substation, overall substation reliability shall be demonstrated.
(3) On-Site Generators. Emergency power may be provided by on-site, automatic
electrical generators sized to operate the station at its firm pumping capacity.
(4) Portable Generators or Pumps. Portable units may be used to guarantee service
provided the final engineering design report includes the location of the unit(s) and the amount of time
which will be needed to transport the unit(s) to the lift station(s); the number of lift stations for which each
unit is dedicated as a backup; what type of routine maintenance and upkeep is performed on the portable
units to ensure that they will be operational when needed and the power reliability records; and,
information detailed in paragraph (1) of this section. If portable units are proposed as a means of
providing service reliability, they shall meet all of the following criteria:
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(A) The lift station shall be equipped with an automatic device for operator
notification;
(B) Operators shall be on call 24 hours per day and knowledgeable in operation
of the portable units;
(C) The station shall be fully accessible during the 100 year flood event;
(D) Station shall be equipped with a properly designed and tested quick
connection; and
(E) The portable unit shall be sized to handle the firm pumping capacity of the
station.
(5) Spill Containment Structures. The use of a spill containment structure as a means of
providing service reliability is prohibited. Spill containment structures may be used in addition to one of
the service reliability options detailed in this section, provided a detailed management plan for cleaning and
maintaining the spill containment structure is discussed in the final engineering design report. Additionally,
any spill containment structures shall be fenced with a six-foot fence which has a minimum of 3 strands of
barbed wire and which has a locked gate. Spill containment structures shall not be used to reduce other
power reliability requirements in any way.
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§217.65. Materials For Force Main Piping.
Force main piping material shall be designed to withstand all working pressures, plus surge
stresses generated by instantaneous pump stoppage due to power failure under maximum pumping
conditions. The use of pipe and fittings rated at working pressure of less than 150 psi is prohibited. All
pipe shall be identified in the technical specifications with the appropriate ASTM, ANSI, or AWWA
specification number for both quality control (dimensions, tolerances, etc) and installation (bedding,
backfill, etc.). Pipe material specified for force mains shall be of a type having an expected life of at least
as long as that of the lift station and shall be suitable for the material being pumped.
§217.66. Force Main Joints.
Joints for force mains in buried service shall be either push-on rubber gaskets or mechanical
joints with a pressure rating equal or greater than the force main pipe material. Joints for exposed force
mains shall be flanged or flexible adequately secured to prevent movement due to surges. Where
possible, ASTM, AWWA, or other appropriate national reference standards for the joints shall be included
in the project specifications.
§217.67. Force Main Pipe Bedding.
Bedding for force mains shall comply with §217.54 of this title (relating to Pipe Bedding).
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§217.68. Identification of Force Main Piping.
A detector tape shall be laid, in the same trench, above and parallel to the force main. The tape
shall state in a minimum of 1½ inch tall letters "pressurized wastewater" continuously along the tape.
§217.69. Force Main Design.
(a) Velocities. Force mains shall be a minimum of 4 inches in diameter unless used in
conjunction with a grinder pump station. For duplex pump stations, minimum force main velocities shall be
3 feet per second with one pump in operation. For pump stations with 3 or more pumps, the force main
velocity shall not be less than 2 feet per second with the smallest pump only in operation unless special
facilities are provided for cleaning the line, or it can be shown that a flushing velocity of five feet per
second or greater will occur once or twice daily. Pipeline velocities greater than 6 feet per second shall
be checked by the engineer for possible high and low negative surge pressures in event of sudden pump
failure.
(b) Detention Time. Detention time of the force main shall be calculated. This calculation shall
be performed using a range of flow rates which represent the flows expected to be delivered to the force
main by the upstream pump station during a 24-hour period.
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(c) Water Hammer. Consideration of surges due to power failure during pumping shall be given
to force mains based upon the wave speed of the force main material to be provided. Surge control
measures shall be provided when pressures due to water hammer exceed the working strength of the
force main pipe.
(d) Connection to Gravity Main. All force mains shall terminate either at a manhole on the
gravity sewer system or at the wastewater treatment system in an appropriate structure or manhole. The
discharge end of a force main inside a manhole shall be designed to remain steady and produce non-
turbulent flow. The top of the force main shall be matched to the top of the design flow depth inside the
receiving sewer pipe where possible. The receiving sewer line shall be designed to handle the maximum
pump discharge without surcharging.
(e) Vertical alignment. Vertical alignment of a pipeline shall avoid, to the greatest extent
practical, following a pump with rapid rises of pipe grade followed by long stretches of flat grade. This
type alignment encourages water column separation resulting in surges. A rising pipe followed by a
falling pipe shall require an air valve at the summit.
(f) Pipe Separation. When installing a force main, the separation distance between the force
main and any existing or new waterline shall meet the minimum separation requirements established in
§290.44 (e) of this title (relating to Water Distribution).
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(g) Odor Control. Force main discharge points shall be arranged to reduce turbulence. Force
mains shall terminate at or near a manhole invert with the top of pipe matching the water level in the
manhole at design flow. Odor control in the force main shall be implemented if the detention time creates
an odor problem.
(h) Air Release Valves in Force Mains. Air release valves or combination air release/air
vacuum valves, suitable for sewer service, shall be provided at all high points along the vertical force main
alignment. These air valves shall have an isolation valve between the air valve and the force main. The
air valves shall be installed inside of a vault for access with a minimum vault size of 48 inches in diameter.
The vault access shall have a minimum opening of 30 inches in diameter. The vault shall be vented.
§217.70. Force Main Testing.
Final plans and specifications shall describe the required pressure testing procedures. A pressure
test of 50 psi above the normal operating pressure of the force main is required on all installations. A
temporary valve for pressure testing may be installed near the discharge point of the force main and
removed after the successful completion of the test. The pump isolation valve may be used as the
opposite termination point. The force main shall be filled with water for the pressure test. The pipeline
shall be held at the designated test pressure for a minimum of 4 hours, and the equivalent leakage rate
shall not exceed 10 gallons per inch diameter per mile of pipe per day.
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§217.71. Reclaimed Water and Irrigation Facilities.
In accordance with §217.9 of this title, (relating to Submittal Requirements), the design of
distribution systems which will convey reclaimed water to a user shall be submitted, reviewed, and
approved by the executive director. The design of the distribution systems shall meet the requirements of
Chapter 217 of this title (relating to Design Criteria for Sewerage Systems). Where a municipality is the
plan review authority for certain sewer systems which transport primarily domestic waste in lieu of the
commission, design submittals will not be subject to submittal to the executive director and instead shall be
approved by the municipality. Reuse facilities which are designed to transport Type II reclaimed water,
as defined by Chapter 210 of this title, shall comply with §217.52 through §217.70 of this subchapter, as
applicable to the project. Reuse facilities designs which are transporting Type I reclaimed water, as
defined by Chapter 210 of this title, may be designed with reduced minimum requirements. The minimum
requirements for Type I reclaimed water facilities are provided in this section.
(1) Gravity Piping in Type I Reclaimed Water Facilities. Lines which transport Type I
reclaimed water in gravity sewers under gravity flow shall meet the requirements detailed in paragraphs
(1)-(5) of this section.
(A) Type I reclaimed water gravity piping shall comply with §§217.53(c), (f),
(h), (j), (l), (n), 217.54, 217.55(1), 217.55(5), 217.58, and 217.59 of this title (relating to Pipe Design, Pipe
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Bedding, Manholes and Related Structures, Testing Requirements for Installed Gravity Collection Lines,
Testing Requirements for Manholes).
(B) Where velocities greater than 10 feet per second will occur when the pipe is
flowing full based on Manning’s formula and an n value of 0.013, special provisions shall be made to
protect against pipe and bedding displacement.
(C) The designer shall consider methods to prevent or maintain lines to mitigate
the effect of the deposition of solids in the gravity conveyance.
(D) Appurtenances Identification.
(i) above-ground hose bibs (spigots or other hand operated connections)
are prohibited. Hose bibs shall be located in locked, below-grade vaults which shall be clearly labeled as
being of non-potable quality. As an alternative to the use of locked, below-grade vaults with standard
hose bibs services, hose bibs which may be only operated by a special tool shall be placed in non-lockable,
underground service boxes clearly labeled as non-potable water; and
(ii) Signs in both English and Spanish shall be posted and maintained at
storage areas, on hose bibs, and at faucets reading "Non-Potable Water, Do Not Drink" or similar
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warnings. Alternatively, the area shall be secured to prevent access by the public. All hose bibs and
faucets shall be painted purple and shall be designed to prevent connection to a standard water hose.
(E) Cross Connection Control - Separation Distances. Type I reclaimed water
piping shall be separated from potable water piping by a distance of at least nine feet, as measured from
the outside surface of each of the respective pieces. Physical connection between a drinking water
supply line and a reclaimed water line is prohibited. Any appurtenance shall be designed and constructed
to prevent any possibility of reclaimed water entering the drinking water system. Where the nine foot
separation distance cannot be achieved, the reclaimed water piping shall meet the requirements in
subparagraphs (A) and (B) of this paragraph.
(i) New Type I Reclaimed Water Line - Parallel Lines. Where a new
Type I reclaimed water line is installed parallel to an existing water line, the horizontal separation distance
shall be no less than three feet (outside to outside) with the water line at the same level or above the
reclaimed water line. The Type I reclaimed water line shall have a minimum pipe stiffness of 115 psi
with compatible joints, or shall have a pressure rating of 150 psi for both pipe and joints. The Type I
reclaimed water lines which parallel the water lines may be placed in the same benched trench, provided
the reclaimed water line is embedded in cement stabilized sand. Where cement stabilized sand is used,
the sand shall have a minimum of 10 percent cement per cubic yard of cement stabilized sand mixture,
based on loose dry weight volume (at least 2.5 bags of cement per cubic yard of mixture. The cement
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stabilized sand bedding shall be a minimum of 6 inches above and one quarter of the pipe diameter on
either side and below the sewer pipe.
(ii) New Type I Reclaimed Water Lines - Crossing Lines. Where a
new Type I reclaimed water line is installed crossing an existing potable water line, one segment of the
Type I reclaimed water pipe shall be centered on the water line such that the joints of the reclaimed water
line pipe are equidistant from the center line of the potable water line. Whenever possible, the crossing
shall be centered between the joints of the potable water line. The Type I reclaimed water pipe shall
have either a pressure rating of 150 psi for both pipe and joints or a pipe stiffness of at least 115 psi with
compatible joints for a minimum distance of 9 feet in each direction as measured perpendicularly from any
point on the water line to the Type I reclaimed water pipe. The minimum distance between a reclaimed
water line and any potable water line shall be 6 inches. Any portions of reclaimed water line within 9 feet
of a potable water line shall be embedded in cement stabilized sand. The cement stabilized sand shall
comply with the same requirements as those listed in subparagraph (A) of this paragraph.
(2) Site Selection of Type I Reclaimed Water Pump Stations. The design shall comply
with §217.60(a)-(c) of this title (relating to Lift Station Site Selection).
(3) Design of Type I Reclaimed Water Pump Stations. The design shall comply with
§§217.61(d), (g), 217.62(d), 217.63(a), (c) of this title (relating to Lift Station Wet Well/Dry Well Design
Considerations, Pump for Lift Stations, Lift Station Piping) and paragraphs (1)-(3) of this section.
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(A) Pump Controls. All electrical equipment shall be protected from, and
operable during, a 100-year flood event and be protected from potential flooding from the wet well.
Motor control centers shall be mounted on a 4-inch tall housekeeping pad.
(B) Pumps. All pumps shall be securely supported so as to prevent movement
or vibration during operation. For submersible pumps, rail-type pump support systems incorporating
manufacturer-approved mechanisms designed to allow the operator to remove and replace any single
pump without first entering or dewatering the wet well shall be provided. Submersible pump rails and
lifting chains shall be constructed of Series 300 stainless steel. The firm pumping capacity of all reuse
pump stations shall be such that the required flow can be pumped to its desired destination. Firm pumping
capacity is defined as total station maximum pumping capacity with the largest pumping unit out of
service.
(C) Lift Station Valving. A check valve shall be installed on the discharge side
of each pump followed by a full-closing isolation valve on each pump. Check valves shall be swing type
with an external lever. Gate valves with rising stems are recommended for full-closing valves. If other
than rising stem gate valves, such as plug valves, are used, then the valves shall include a position
indicator to show their open or closed position.
(4) Force Main Piping for Type I Reclaimed Water. The design shall comply with §§217.65,
217.66, 217.67, 217.69(a)-(c), (e), (h), 217.70, of this title (relating to Materials for Force Main Piping,
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Force Main Joints, Force Main Pipe Bedding, Force Main Design, and Force Main Testing) and
paragraphs (1) and (2) of this section.
(A) Identification. The force main pipe shall be purple in color or contained in a 8 mil
polyethylene sleeve conforming to AWWA C105, Class C, that is purple in color.
(B) Isolation Valves. In-line isolation valves for reuse pipes shall open clockwise to
distinguish them from potable water isolation valves. Valve casings for underground isolation valves shall
have cast into the cast iron lid "REUSE" or "NPW."
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SUBCHAPTER D : ALTERNATIVE SEWER COLLECTION SYSTEMS
§§217.91-217.100
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code as well as the authority to set standards to prevent the
discharge of waste that is injurious to the public health under §26.041 of the Texas Water Code.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.91. Applicability.
This subchapter sets forth the design criteria for alternative sewer collection systems.
§217.92. Design of Alternative Collection Systems - Component Sizing.
Components shall be sized based on existing flow data from similar types of systems and service
areas, whenever such data is available. If flow data from similar service areas with conventional
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wastewater collection systems are used, consideration shall be given to the effects of inflow and
infiltration on the peak flows of the system. Design and construction of alternative wastewater collection
systems shall be done to minimize excess flows from inflow and infiltration. Roof, street, or other types of
drains that permit entrance of surface water into the sanitary sewer system are prohibited.
(1) On-Site Components. In the absence of existing data, Table B.1 in §217.32 of this
title (relating to Design of New Systems - Organic Loadings and Flows), in conjunction with the following
formula, shall be used for sizing on-site components in residential systems: Figure 1: §217.92(1)
Q’X( (1%B) Equation 1.d
Where: Q = flow in gallons per day
X = per capita wastewater production
B = number of bedrooms
(2) Off-Site components. Design of the off-site components shall be based on the
maximum flow rate expected. The maximum flow rate shall be calculated by the following formula:
Figure 2: §217.92(2)
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Q’A( N%B Equation 2.d
Where: Q = Design flow rate (gallon per minute)
A = Design coefficient, typically 0.5
N = Number of EDUs served by the off-site component
B = Safety factor, assumed to be 20.0
(A) An EDU is assumed to have an occupancy of 3.5 people. For significantly
Q’A1(P%B Equation 3.d
different occupancy rates, the following formula shall be used: Figure 3: §217.92(2)(A)
Where: Q = Design flow rate (gallon per minute)
A1 = Derived from A in previous equation, typically 0.15
P = population to be served
B = Safety factor, assumed to be 20.0
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(B) The safety factor, B, may be adjusted if high wastewater flows are
anticipated. Discharges from commercial or institutional dischargers shall be measured directly or
calculated as previously indicated.
§217.93. Gravity Lines, Force Mains and Lift Stations in Alternative Collection Systems.
Except where specifically modified in this subchapter, designs for alternative sewer collection
systems shall comply with the applicable requirements of Subchapter C of this Chapter, in addition to the
requirements of this subchapter. The manager/operator of the alternative collection system shall comply
with all the requirements of this subchapter and shall ensure that all components which are a part of the
any alternative collection systems which are covered by a sewer service agreement are designed,
constructed and operated in compliance with all the requirements of this subchapter and any other
applicable rules. An operations and maintenance manual covering the recommended operating
procedures and maintenance practices for the alternative wastewater collection system and record
drawings indicating the location of all on-site components of the alternative wastewater collection system
shall be provided to the owner by the engineer, upon the completion of construction. The engineer shall
submit a letter to the Commission’s Wastewater Permitting Section certifying that this action has been
performed. The letter shall include:
(1) A copy of the operation and maintenance manual, and/or the record drawings to the
commission upon request.
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(2) Permit number and names of the permittee.
§217.94. Management.
A management structure shall be established to be responsible for the operation and maintenance
of an alternative wastewater collection system.. The manager/operator of the alternative collection
system shall comply with either paragraphs (1) or (2) of this section.
(1) The manager/operator of the alternative collection system shall be the same as the
entity that holds the wastewater discharge permit for the facility treating the sewage collected by the
alternative collection system. When the manager/operator does not hold a wastewater discharge permit
and as such contracts by written agreement with another entity for wastewater treatment, then that
agreement shall address the responsibility for management and operation of the alternative collection
system. Regardless of which entity takes responsibility for management and operation of the alternative
collection system, it must be an entity under jurisdiction of the commission
(2) The manager/operator of the alternative collection system may contract for
management and operation services by a public or private service provider. The manager/operator shall
have the authority to terminate the contract at any time if the service provider’s services are in conflict
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with the manager/operator’s requirements or wastewater discharge permit, the requirements of this
chapter, or other commission requirements.
(3) Grinder pumps and septic tank effluent pumps, discharging directly into a
conventional gravity sewer system, are not required to comply with the requirements for management.
§217.95. Sewer Service Agreements.
A sewer service agreement shall be executed between the manager/operator of the alternative
wastewater collection system and the property owner that allows for the placement and maintenance of
alternative system components located on private property. The sewer service agreement between the
property owner and the manager/operator of the alternative system shall insure that proper construction
and competent maintenance of the on-site components shall be executed. The on-site components may
be owned by the property owner, or the manager/operator. The sewer service agreement shall be
submitted to the commission with the summary transmittal letter required in §217.9(c) of this title (relating
to Summary Transmittal Letter). Regardless of the ownership of the on-site components, a sewage
service agreement for alternative collection systems shall include the following provisions.
(1) Any existing alternative sewer system components, including building laterals that
are to be incorporated into an alternative collection system shall be cleaned, inspected, tested, repaired,
modified or replaced, as necessary, to the satisfaction of the manager/operator of the alternative
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wastewater collection system prior to connection of these components to the collection system, to insure
the integrity of, and the compatibility to, the alternative wastewater collection system.
(2) The manager/operator of the alternative wastewater collection system shall have
final approval for all materials and equipment prior to the incorporation of the materials and equipment into
any construction or repair of alternative sewer system components.
(3) The manager/operator of the alternative wastewater collection system shall inspect
and approve the actual installation of all alternative sewer collection system components prior to placing
the components into service.
(4) The manager/operator of the alternative wastewater collection system shall be
granted access at all reasonable times to inspect alternative sewer collection system components.
(5) The manager/operator of the alternative wastewater collection system shall be
granted the right to make emergency repairs and perform emergency maintenance to any alternative
sewer collection system components, including building laterals, and utility-owned on-site collection system
components, in order to protect the integrity or operation of the alternative system. The agreement shall
provide that the cost of such repairs or maintenance will be charged to the owner of the property, provide
a means to determine the cost of such repairs, provide a schedule of payment, and provide for a
methodology for cost recovery.
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(6) For those alternative collection system designs that incorporate alternative collection
system components that use power, the service agreement shall provide for the delineation for
responsibility for power costs. Power for alternative collection system components serving an EDU may
be supplied from the electrical service equipment serving the EDU. Power for alternative collection
system components serving a MEDU shall be supplied separately from the MEDU.
(7) When a MEDU, because of the nature of its wastewater, shall employ pre-treatment
units, ownership and responsibility for the operation and maintenance of the facilities shall remain with the
MEDU unless otherwise agreed to by the manager/operator of the alternative collection system.
Regardless of ownership, a sewer service agreement between the owner of the pre-treatment units and
the manager/operator of the alternative collection system shall be executed. The agreement shall grant
the manager/operator of the alternative collection system the right to inspect and approve the installation
of any pre-treatment units, allow access for inspection of the units to determine their operational and
maintenance status, and allow the manager/operator of the alternative wastewater collection system to
make emergency repairs or perform emergency maintenance when required to protect the integrity or
operation of the alternative wastewater collection system. The agreement shall provide that the cost of
such repairs or maintenance will be charged to the owner of the pre-treatment units, provide a means to
determine the cost of such repairs or maintenance, provide a schedule of payment, and provide for a
methodology to recover costs.
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(8) A utility-owned service isolation valve shall be provided upstream of any utility-
owned, on-site component. When the on-site components are privately owned, the service isolation valve
shall be located on the service line from the on-site components to the collection system, and as close as
practical to the property line. The location of the service isolation valve shall be accessible at all times by
the utility through an easement granted by the property owner to the utility or other means which
guarantees access. The manager/operator shall be given access to the isolation valve at all times.
(9) The manager/operator of the alternative wastewater collection system shall
demonstrate a capacity to manage any residual materials that may be generated by use of an alternative
wastewater collection system. Management shall include the ability to collect, transport, and dispose of
the residual materials.
§217.96. Design of Small Diameter Effluent Sewers (SDES).
(a) Interceptor tank design. Septic tanks used as interceptor tanks shall be designed and
constructed in accordance with Chapter 285 of this title (relating to On-site Sewage Facilities). A
commercially available effluent filter shall be installed on the outlet of the interceptor tank. The effluent
filter shall be designed to remove particles larger than 1/16 inch and shall be designed and installed to
facilitate easy cleaning. The volume of an EDU interceptor tank shall be based the criteria in Chapter
285 of this title (relating to On-site Sewage Facilities). MEDU interceptor tank sizing will be based on the
formula: Figure 1: 217.96(a)
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VT’VR%VN Equation 4.d
Where: VT = Total Volume
VR = Reserve Volume = 0.75 x average daily flow (ADF)
VN = Nominal Volume
VN’VIE%VCZ%VSO Equation 5.d
Where: VIE = Volume in gallons between elevation of the tank inlet and
the tank outlet ( #.165 ADF)
VCZ = Volume in gallons of the clear zone between
maximum sludge depth and scum accumulation
(ADF)
VSO = Volume in gallons dedicated to scum and sludge
storage (1.85 ADF)
(b) Pre-treatment units. MEDU establishments that discharge wastewater with excessive
amounts of fats, oils, or grease shall provide a method for trapping and removing these constituents from
the wastewater before the interceptor tanks. Grease traps shall be of a double compartment design.
Construction requirements of grease traps shall meet the same requirements as interceptor tanks with
regard to water tightness, materials of construction and access to contents. Grease retention capacity in
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pounds shall be equal to at least twice the unit's flow capacity in gallons per minute. The grease retention
capacity of the trap is defined as the amount of grease that it can hold before its efficiency drops below
90%. The primary compartment volume shall be at least 60% of the total tank volume. Plumbing for the
grease trap shall be designed to exclude waste from other fixtures, specifically blackwater, from entering
the trap.
(c) Tank monitoring. The manager/operator of the SDES shall monitor the sludge volume in
each interceptor tank. Before the sludge level is within 6 inches below the outlet, the interceptor tank
shall be pumped.
(d) Service line design. Pipe materials used for service lines shall meet the performance
characteristics of ASTM D 2241 Class 200 PVC pipe. Interceptor tanks with outlet elevations below the
main line elevation, or the hydraulic grade line in the depressed section of a main line, shall be designed
with pumping units. The minimum acceptable diameter for a service line serving an EDU is 2 inches.
Service lines for MEDUs shall be a minimum of 2 inches in diameter, but shall be designed based on the
actual hydraulic requirements. Diameter of service lines shall be no greater than the collection line to
which they connect. Service lines of low-lying interceptor tanks, that are subject to periodic back flow
shall be fitted with a check valve. The check valve shall be located immediately adjacent to the collection
line. Check valves shall be made from a corrosion resistant material and provide an unobstructed flow
way. A means to prevent the migration of odors from the collection line by use of traps or other in-line
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odor control devices shall be provided. The odor control devices shall be readily accessible for
maintenance.
(e) Collection system design.
(1) Hydraulic design. All SDES systems designed for open channel flow shall use a
design depth of flow of 100% of pipe diameter. Flow velocities in collection lines shall not be less than 1.0
feet per second at design flow nor greater than 8 feet per second at peak flows without velocity
protection. In no case shall the flow velocity exceed 13 feet per second in any portion of the SDES
system. Velocity calculations for each line segment shall be submitted with the final engineering design
report. Design of SDES shall insure that the elevation of the hydraulic grade line at peak flow conditions is
lower than the outlet invert of any upstream interceptor tank, except those which incorporate the use of
septic tank effluent pumps as on-site conveyance equipment. A system analysis for each line showing the
hydraulic grade line, energy grade line, and ground elevation in relationship to the outlet elevations of the
interceptor tanks being served by the collection line shall be included in the final engineering design report
accompanying the plans. When an SDES system is comprised of both open channel and pressure flow
segments, as found in VGES systems, separate analysis shall be made for each segment of the sewer in
which the type of flow does not change. For open pipe flow, a Manning’s "n" value of 0.013 shall be
used. For pressure flow a Hazen-Williams "C" value of 120 shall be used. The minimum pipe diameter
for an SDES shall be 2-inches.
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(2) The vertical alignment of an SDES may be variable; however, the overall gradient
shall provide sufficient fall such that the lines have sufficient capacity to transport the expected peak
flows. The invert elevation of a section of a collection line, which is depressed below the static hydraulic
grade line, shall be at an elevation that does not permit the hydraulic grade line to rise above any upstream
interceptor tank outlet invert at peak flow, except those which are equipped with septic tank effluent
pumps. Venting shall be provided upstream and downstream of line segments that are below the
hydraulic grade line. The profile of the sewer lines shall be uniform with no abrupt or sharp changes in
profile. Cleanouts shall be used in lieu of manholes at upstream termini of collection lines, minor junctions
of collection lines, changes in collection line diameter, and at intervals along a collection line. Maximum
spacing of cleanouts along collection lines shall be 1000 feet. Cleanouts shall extend to ground level and
terminate in watertight valve boxes. Manholes shall be used at intersections of 3 or more collection lines.
Manholes shall not be located in the flow path of water courses or drainages, nor in areas where ponding
of surface water is probable. Wastewater service air release or combination air release/vacuum valves
shall be used for venting at summits in the collection lines, and where otherwise needed for proper
operations. The valves shall be constructed of corrosion resistant material and located in watertight
vaults. Piping materials used in the collection system shall meet the performance requirements of ASTM
D 3034 SDR 26 PVC pipe, except for those segments under pressure flow conditions where piping
materials shall meet the performance requirements of ASTM D 2241 Class 200 PVC pipe.
§217.97. Design of Pressure Sewers.
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Pressure sewer systems include grinder pump sewer systems and septic tank effluent pump
systems. Except where this section specifically states otherwise, the requirements of this section apply to
both of these types of systems.
(1) Service Line Requirements. Pressure sewer service lines buried at a depth of less
than 30-inches shall incorporate a check valve and a fully closing gate or ball valve at the connection to
the collection line to allow isolation of the service line. Check valves shall be of a design that allows an
unencumbered flow. Valves shall be manufactured from corrosion resistant material and shall incorporate
a position indicator to show their open and closed position. Minimum size service line for an EDU is 1.25
inches and for a MEDU the minimum size service line is 1.5 inches. Connection to collection lines shall be
made by tee or service saddle. Solvent weld fittings may be used. The diameter of a service line shall be
no greater than the collection line to which it connects. Materials used in service line piping shall at least
be equivalent to the performance characteristics of ASTM D 2241 Class 200 PVC pipe.
(2) On-Site Pressure Sewer System Mechanical Equipment Requirements.
(A) Pump discharge rates shall be such that the expected wastewater peak flow
can be accommodated by the capacity of the pump and by the volume of the wet-well dedicated for flow
attenuation and storage. The engineering report shall include an engineering analysis which justifies the
selected pump(s).
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(B) Simplex units may be provided for an EDU; however, a MEDU shall be at
least a duplex unit which is capable of pumping the peak flow with the largest pump out of service.
(C) Calculations shall be done to show that lift stations and pump chambers are
protected against buoyancy forces.
(D) Control panels for all pumps shall be at least 2 feet above the ground floor
elevation of the structure being served by the equipment.
(E) All piping and appurtenances within the wet wells shall be corrosion
resistant.
(F) The reserve volume of an EDU grinder pump wet well or a STEP wet well
shall be at least 100 gallons after the activation of the high water alarm level. The reserve volume of a
MEDU grinder pump wet well shall be equal to the volume accumulated during the peak 2-hour period, or
100 gallons, whichever is greater. Pumps located in STEP chambers that are integral with the interceptor
tank may use the reserve volume of the interceptor tank for the required reserve volume. Housings that
contain the mechanical equipment or its controls shall be watertight when immersion of equipment or
controls will cause their failure.
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(G) A visual and audio alarm shall be provided with all wet wells. For EDUs the
alarms shall activate at a specified high water level. For MEDUs the alarms shall activate in the event of
unit failure or high water level.
(H) Control panels and other electrical enclosures shall be constructed from
corrosion resistant materials, shall be water tight, and shall be designed and installed in a manner to
prevent the migration and venting of odors and corrosive or explosive gases to the panel. All electrical
equipment shall bear the seal of the Underwriter Laboratory, Inc., or shall comply with the National
Electric Code.
(I) On-site mechanical equipment used in STEP systems may be either housed
in the interceptor tank or in a separate stand alone unit. Pumps used in STEP systems shall be located in
a hydraulically independent chamber. The pump chamber shall be hydraulically connected to the
interceptor tank such that the liquid elevation in the pumping chamber is independent of the liquid elevation
in the interceptor tank. Designs that allow direct pumping of the contents of the interceptor tank such that
the liquid elevation in the tank fluctuates shall not be used.
(J) All on-site mechanical equipment and their control mechanisms shall be
housed in lockable or similar tamper-resistant structures. Vaults, chambers, wet-wells or other structures
used to detain wastewater which are integral with structures that contain on-site mechanical equipment
shall be watertight and able to withstand all expected structural loadings. Materials used for equipment
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housings and detention of wastewater shall be corrosion resistant and meet the same requirements with
regard to materials of construction as interceptor tanks.
(3) Discharge Piping Requirements. All discharge piping and connections used to
connect the on-site mechanical equipment to the service line shall be pressure rated at a minimum of 2.5
times the maximum system design pressure. Piping material and valves shall be corrosion resistant and
otherwise suitable for exposure to a sewage environment. For discharge piping that incorporates the use
of plastic hoses, direct burial of the hose shall not be allowed. Discharge piping for pressure systems shall
include a check valve, pipe union and a full closing gate or ball valve. The check valve shall precede the
full closing valve. Valves shall incorporate a position indicator to show their open and closed position.
Valves used in MEDU applications shall be housed in a valve box separate from the on-site mechanical
equipment.
(4) Collection System Design. Consideration shall be given to ensuring that grinder pump
pressure system main lines are designed to achieve velocities of 3 feet per second at least once per day.
Under no circumstances shall design velocities be less than 2 feet per second. Velocities in grinder pump
main lines shall not exceed 8 feet per second. Septic tank effluent pump pressure system main lines shall
achieve velocities of 1 foot per second at least once per day. Collection system headloss calculations
shall be based on a Hazen-Williams “C” factor appropriate to the piping material, but “C” factors of
greater than 120 are not allowed. Minimum size piping used for pressure system collection lines shall be
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1.5 inches. Material characteristics shall be at least equal to ASTM D 2241 Class 200 PVC pipe.
Elastomeric pipe joints shall be required for pipe equal to or greater than 3 inches in diameter. Air relief
shall be provided at the locations where air may accumulate due to a transition between full and partially
full flow conditions. Pumping units affected by the partially full flow conditions shall incorporate anti-
siphon devices. Isolation valves shall be located at intersections of collection system main lines, both sides
of stream crossings, both sides of areas of unstable soil, and at maximum intervals of 2,500 feet on long
routes. Isolation valves shall be resilient seated gate valves or ball valves, with a position indicator, and be
constructed from corrosion resistant materials. Isolation valves shall be located in locked valve boxes.
Wastewater type air release valves constructed from corrosion resistant materials shall be provided at all
significant peaks in elevation. The valve orifice shall not be less than 0.25 inches in diameter. Air release
valves in close proximity to residences shall incorporate a method to control odor released by their
operation. When intermediate pumping of the wastewater is required, the design of the collection system
lift stations shall meet the requirements of Subchapter C.
§217.98. Vacuum Sewer Systems.
Vacuum Sewer Systems shall be considered nonconforming technologies. If a review of a
vacuum sewer is performed by the executive director, the review will be done in accordance with
§217.10(b) of this title (relating to Types of Approvals) and the criteria described in this section.
(1) Design of Vacuum Sewers.
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(A) On-Site Components-The building lateral shall be constructed from a piping
material that is at least equivalent in performance to ASTM D 2241 Class 160 PVC pipe. The building
lateral shall have a screened, auxiliary vent, no less than 4-inches in diameter located no closer than 10
feet from the vacuum valve. Vacuum valve controls shall be housed in tamper resistant, watertight,
corrosion resistant structures. Vacuum valve pits shall be watertight with regard to surface and
groundwater inflow. Control mechanisms that incorporate pressure differential for operation shall use
atmospheric air supplied by a screened breather vented externally to the equipment housing. Vacuum
valves shall have a minimum capacity of 30 gallons per minute. Service lines shall be a minimum of 3
inches in diameter. Materials used in the construction of service lines shall have performance
characteristics at least equivalent to ASTM D 2241 Class 200 PVC pipe. All joints shall be made be
either vacuum rated Elastomeric gaskets, or by solvent welding. There shall be at least 5 feet of service
line between the vacuum valve and the main line. When vertical profile changes are incorporated in
service lines, there shall be a minimum of 5-feet between the vacuum valve and first profile change, and
between the last profile change and the main line. Service lines shall have a minimum slope equal to the
greater of a 2-inch drop or 0.2% slope between the vacuum valve and main collection line, or between
vertical profile changes. Connection of service lines to main lines shall be done using a wye and a long
radius elbow, oriented so that the invert of the service line is higher than the crown of the collection line,
and shall not be made within 6-feet of a collection line vertical profile change.
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(B) Collection System Design. All piping used in vacuum sewers shall be
equivalent to the performance characteristics to ASTM D 2241 Class 200 PVC pipe. Joints shall be
made with vacuum rated rubber gaskets or by solvent welding. The minimum sized pipe used in vacuum
sewers shall be 4-inches in diameter, except for service lines which may be 3-inches in diameter. The
length of a 4-inch diameter line shall not exceed 2,000 feet; lengths for other larger diameter lines shall be
dictated by friction and lift head loss. The total available head loss in a system shall not exceed 18 feet.
Friction headloss for any sized pipe shall be limited to 0.0025 ft./ft. Head loss calculations shall be
submitted with the engineering report. Vacuum sewer systems shall be laid out in a branched pattern.
The line work shall have a sawtooth profile that slopes toward the vacuum station. Slope profile of the
collection line shall be the greater of 0.2% of the distance slope, ground profile, or 40% of pipe inside
diameter except for 4-inch pipe where 80% inside diameter is to be used. Design of upgrade mainline
transport must reduce the risk of completely blocking the pipe bore with trapped sewage. Collection lines
that must be depressed in order to avoid an obstruction shall have a minimum 20-foot segment centered
on the obstruction. Division valves shall be provided at collection line intersections, at both sides of a
watercourse crossing and areas of unstable soils, and at intervals of 1,500 feet. Plug valve or resilient
seated gate valves, capable of sustaining a vacuum of 24 inches of mercury are acceptable. Gauge taps
shall be provided downstream of the division valve. Cleanouts shall be provided at changes in pipe
diameter, and on collection line segments of 1500 feet or more where there are no service connections.
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(C) Vacuum station design. The minimum vacuum pump capacity shall not be
less than 150 gpm, and shall be the greater of the capacities calculated using the following equations:
Figure 1: §217.98(1)(D)
Qvp = [A Qmax/7.5 gal./ft.3] + B Nv
Where:
Qvp = Minimum vacuum pump capacity
A = Variable based on line length
Qmax = Station peak flow (gal./min.)
B = Bleed rate of vacuum valve controller (ft.3/min.)
Nv = Number of vacuum valves in system
The appropriate values of A shall be as follows:
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Longest Line Length
(ft.) A
0 - 3,000 5
3,001 - 5,000 6
5,001 - 7,000 7
7,001 - 10,000 8
10,001 - 12,000 9
12,001 - 15,000 11
Or,
Q = V/PDT ln (H1/H2)
Where:
Q = Flow rate of vacuum pump (ft.3/sec.)
PDT = Time to reduce head from H1 to H2 (sec.)
V = Volume of closed system (ft.3)
H1 = Initial absolute pressure head (in. mercury)
H2 = Final absolute pressure head (in. mercury)
(D) Vacuum Pumps. Vacuum pumps must be sized to evacuate the system in no
more than 180 seconds. Duplicate pumps, each capable of delivering 100% of required air-flow, and
capable of continuous duty shall be provided. Either liquid-ring or sliding-vane type vacuum pumps may be
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used; however, liquid-ring pumps shall be sized 15% larger than the needed vacuum pump capacity. An
electrically or pneumatically controlled plug valve between the collection tank and reservoir tank shall be
included in the station piping to prevent carry over of liquid into the pumps.
(E) Duplicate discharge pumps. Duplicate discharge pumps, each capable of
delivering the peak flow, shall be provided. Pumps shall be designed for vacuum sewage duty, and have
equalizing lines installed. Pumps shall be capable of passing a 3-inch sphere and constructed from
corrosion resistant materials. Double mechanical shaft seals shall be used on the discharge pumps.
Discharge pumps shall have shut off valves on both the suction and discharge piping. Total dynamic head
calculation shall consider the head attributed to overcoming the vacuum in the collection tank. The
available NPSH must be greater than required NPSH for the expected vacuum operating range. Pump
suction lines shall be sized 2 inches larger than the discharge lines to prevent vortexing of wastewater in
the collection tank. Pump design calculations and pump curves shall be submitted with the engineering
report.
(F) Vacuum Reservoir. A vacuum reservoir tank shall be provided in addition to
the collection tank for vacuum systems that require a collection tank of 1600 gallons or greater. When a
vacuum reservoir tank is used, the vacuum pumps shall be piped directly to top of the reservoir tank.
Minimum size for a reservoir tank is 400 gallons. Provision shall be made in the design of the tanks for
internal access for periodic cleaning and inspection. All main lines shall connect directly to the collection
tank. The wastewater pump suction lines shall be placed at the lowest point on the collection tank and as
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far as possible from the main line inlets. The main line shall enter at the top of the collection tank with the
inlet elbows inside the tank turned at an angle from the pump suction opening. Liquid level sensing for
operation of the discharge pumps shall be by probes or other devices in the collection tank. Vacuum
pumps shall be controlled by vacuum switches located in the reservoir tank. Alarms for high liquid level in
the collection tank and low system vacuum shall be provided.
§217.99. Testing Requirements for Alternative Sewer Collection Systems.
All components of alternative wastewater collection systems shall be tested for water tightness
by methods as shown in Table D.1. Figure 1: §217.99
Table D.1 - Testing Requirements for Alternative Sewer Collection Systems
Component Type of Test(s)
Interceptor Tanks H.H.T. or V.T.T.
Buffer Tanks H.H.T. or V.T.T.
Vaults, Pits, Wet Wells H.H.T. or V.T.T.
Service Lines (Pressure) P.L.T.
Service Lines (SDES) H.H.P.
Collection Lines (Pressure) P.L.T.
Collection Lines (SDES) L.P.A. or H.H.P.
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Where:
H.H.P. = Hydrostatic head test for linework
H.H.T. = Hydrostatic head test for tanks
L.P.A. = Low pressure air test for linework
P.L.T. = Pressure line test
V.T.T. = Vacuum test for tanks
(1) Hydrostatic Head Test for Linework. The total infiltration or exfiltration, as
determined by the hydrostatic head test, shall not exceed 10 gallons per inch diameter per mile of pipe per
24-hours at a minimum head of two feet. If the quantity of infiltration or exfiltration exceeds the maximum
quantity specified, remedial action shall be undertaken in order to reduce the infiltration or exfiltration to
an amount within the limits specified.
(2) Hydrostatic Head Test for Tanks. Tanks shall be tested in place before placement of
backfill. The tank will be filled to the top of the lid and allowed to stand for 24- hours. No leakage will be
allowed. Tanks constructed from flexible or semi-rigid material shall be placed and backfilled in
accordance with manufacturer’s recommendations, then tested according to the above procedure.
(3) Low Pressure Air Test. The low pressure air test shall conform to the requirements
of §217.58(1) of this title (relating to Testing Requirements For Installed Gravity Collection Lines).
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(4) Pressure Line Test. Leakage shall be defined as the quantity of water that shall be
supplied into the pipe or any valved section thereof, to maintain pressure within 5 pounds per square inch
of the specified test pressure after the air in the pipeline has been expelled. The test pressure shall be
either a minimum of 25 pound per square inch gauge or 1.5 times the maximum line design pressure,
whichever is larger. The maximum allowable leakage shall be calculated using the formula below. If the
quantity of leakage exceeds the maximum amount calculated, remedial action shall be taken to reduce the
leakage to an amount within the allowable limit. Figure 2: §217.99 (4)
L’ (S(D(P 0.5)/133,200 Equation 5.d
Where:
L = Leakage (gal./hr.)
S = Length of pipe (ft.)
D = Inside diameter of pipe (in.)
P = Pressure (psi)
(5) Vacuum Test for Tanks. The total vacuum loss, as determined by this test, shall not
exceed 1 inch loss of mercury vacuum after 5 minutes. Additionally, for tanks constructed of flexible or
semi-rigid material, the maximum allowable change in tank dimensions shall be 3% in any direction. The
test will commence only after the establishment of an initial stable vacuum of 4-inches of mercury. If the
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quantity of vacuum loss or if tank deformation equals or exceeds the maximum quantity specified, then
remedial action shall be undertaken in order to reduce the amount of vacuum loss or amount of
deformation to comply with the criteria.
§217.100. Termination Facilities for Alternative Sewer Collection Facilities.
Termination of an alternative wastewater collection system at treatment facilities or into an
existing conventional sewer within close proximity of human habitation shall be designed to minimize the
potential for odors. Release of gases shall be controlled by incorporating methods that minimize turbulent
discharge of the alternative sewer into manholes, and discharge shall be into manholes that have a high
ratio of conventional flow to alternative flow. Alternative sewers that discharge at wastewater treatment
systems shall discharge below the liquid level at the headworks. Consideration shall also be given to the
corrosive nature of alternative wastewater system sewage in the materials used in the termination
facilities.
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SUBCHAPTER E : PRELIMINARY TREATMENT UNITS
§§217.121-217.138
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code as well as the authority to set standards to prevent the
discharge of waste that is injurious to the public health under §26.041 of the Texas Water Code.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.121. Applicability.
This subchapter deals with preliminary and primary treatment systems used at wastewater
treatment systems. These treatment systems may help limit damage to, and possible disturbance of,
downstream unit processes and operations. These treatment systems may also be used to optimize the
treatment process for a particular treatment unit.
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§217.122. Coarse Screening Devices.
A coarse screening device, such as a bar screen, should be considered at all wastewater
treatment facilities.
§217.123. Coarse Screening Devices - Redundancy Requirements.
Bypass channels, sized to handle the two-hour peak flow of the facility, shall be provided to
bypass flow around any coarse screening device. Where mechanically cleaned coarse screening devices
are utilized in the primary channel, the bypass channel shall be equipped with a manually cleaned coarse
screening device. A means of diverting flow to the bypass channel shall be provided.
§217.124. Design of Coarse Screening Devices.
(a) Location Requirements. All coarse screening devices installed in an enclosed structure
containing other equipment or offices shall be designed with a separate entrance and shall be separated
from all areas by gas tight partitions. All screening device enclosures shall be equipped with a vent fan
capable of provided at least 30 air exchanges per hour when the space is configured to allow personnel
entry. All screening devices shall be located so they are readily accessible for maintenance and
screenings removal. Screening devices located four or more feet below ground level shall be provided
with equipment capable of lifting the screenings to ground level.
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(b) Screen Openings. Coarse screen bar openings, the clear distance between individual bars,
shall not be less than ½ inch for manually cleaned screens and 1/4 inch for mechanically cleaned
screens. Maximum clear openings shall not exceed 1¾ inches. Manually cleaned screens shall be
constructed with a bar rack sloped at 30 to 60 degrees from the horizontal. For manually cleaned screens,
the bar rack shall be attached to a horizontal platform with provisions to drain and temporarily store the
screenings.
(c) Hydraulics. The velocity through the coarse screen bar racks shall be between one and three
feet per second at design flow. Manually cleaned screens shall have a minimum submerged bar rack
cross-sectional area (wetted area of the screen) of 200% of the inlet channel area based on the peak
flow. The inlet channel for screening devices shall be desinged to minimize deposition of solids. The flow
line of the inlet channel shall not be greater than 6-inches below the invert elevation of the incoming
sewer.
(d) Corrosion Resistance of Screens and Their Structures. All structures, equipment, and
materials associated with coarse screening devices shall be designed to resist the effects of corrosive
environments, .including the effects of long-term exposure to hydrogen sulfide.
§217.125. Coarse Screening Devices - Screenings and Debris Handling.
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Facilities shall be provided for the storage of a minimum of one-day of screenings and debris.
Screenings and debris containers shall be equipped with a tight fitting cover. Suitable drainage facilities,
which drain to the head of the plant, shall be provided for all screenings storage areas. Runoff control
shall be provided around all screenings storage areas. All screenings and debris collected should be
managed and disposed of in accordance with Chapter 330 of this title (relating to Municipal Solid Waste).
§217.126. Fine Screens .
Fine screens are not required, but may be used in lieu of coarse screening devices. Fine screens
are any sreen with a clear opening less than or equal to 1/4 inch.
§217.127. Fine Screens - BOD5 Removal.
Fine screens shall not be considered equivalent to primary sedimentation. The use of fine
screens in lieu of primary sedimentation units is acceptable; however; if the engineer’s design of
downstream treatment units is based on reduction by the fine screen, the reduction percentage shall be
developed through testing and studies conducted on actual full scale operation of the fine screen unit
proposed. The justification for reductions in treatment unit sizes, based on removal of BOD5 from the use
of fine screens, shall be detailed in the final engineering design report.
§217.128. Fine Screens - Redundancy Requirements.
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Where BOD5 reduction is credited through the fine screen, dual fine screen treatment trains shall
be provided. Designs using fine screen units, which claim credit for BOD5 reduction, shall include a
sufficient number of fine screen units so that any BOD5 reductions claimed in the engineering report may
occur with the largest fine screen unit assumed out of service. Fine screens may be installed as single
units where BOD5 reduction will not be credited through the fine screen; however, a bypass channel with
a coarse screening device shall be installed in these cases to accept flow when the fine screen is out of
service.
§217.129. Fine Screen Design Parameters.
Fine screens shall be proceeded by a coarse screening device unless manufacturers
recommendations include installation of the unit without such preliminary screening devices, or historical
data from similar installation is provided. The engineer shall consider the necessity for removal of oils and
grease prior to the fine screen. A continuous cleaning device, such as water jets or wiper blades, shall be
incorporated in the design of moving or rotating fine screens. The fine screen shall have provisions for
the automatic conveyance of material removed by the fine screen to a process which complies with
§217.125 of this title (relating to Coarse Screening Devices - Screenings and Debris Handling). Fine
screens shall be designed to meet manufacturer’s recommendation with respect to velocity and head loss
through the fine screen. Fine screen openings shall be 1/4 inch or less. Fine screens maybe constructed
using bars or perforated plate.
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§217.130. Fine Screens - Screenings and Debris Handling.
Screenings and debris from fine screens shall be managed and disposed of in accordance with
§217.125 of this title (relating to Coarse Screening Devices - Screenings and Debris Handling).
§217.131. Grit Removal Facilities.
Grit removal should be considered for all wastewater treatment plants. Grit removal includes
those units and processes capable of removing inert unbiodegradable particles.. Grit removal facilities are
required for all wastewater treatment systems using anaerobic digesters. Grit removal facilities are
optional for all other facilities.
§217.132. Grit Removal Chambers - Redundancy Requirements.
Dual Grit Removal Processes shall be provided whenever grit removal is required. When dual
grit removal units are installed, each unit shall be capable of operation at the permitted two hour peak flow
of the wastewater treatment system. When single grit removal units are installed a bypass channel shall
be installed to accept flow when the grit removal facilities are off line. A means of diverting flow to the
bypass channel shall be provided.
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§217.133. Design Requirements for Various Types of Grit Chambers.
(a) Horizontal Flow Grit Chambers. Velocity through the grit chamber shall generally not be less
than 0.8 feet per second, nor greater than 1.3 feet per second, during minimum and maximum flow
periods. The grit chamber channel shall be designed to minimize turbulence and shall provide uniform
velocity across the channel. The channel shall be sized in accordance with the grit removal equipment
capacity and shall accommodate grit storage.
(b) Aerated Grit Chambers. The air diffusers and baffle arrangements should be designed to
separaate the size of grit planned for removal. The aeration equipment shall be capable of varying air
feed rates along the length of the chamber from 3 to 8 scfm per linear foot. A minimum hydraulic
detention time of 3 minutes shall be provided based on the permitted two-hour peak flow of the facility.
The chamber shall be designed with a grit hopper. The grit hopper shall be located under the air diffuser.
Square Aerated Grit Chambers
(c) Mechanical Grit Chambers. The velocity through mechanical grit chambers shall be 1 foot
per second at the design flow. The channel shall provide a grit hopper at the side of the tank contiguous
to the grit removal mechanism. The inlet shall be provided with baffles to prevent short circuiting. Grit
removal shall be provided by a reciprocating rake, screw conveyor, or air lift pump.
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(d) Cyclonic Degritters. The cyclone shall be designed to prevent entry-to-overflow short
circuits. An adjustable apex with a quick disconnect assembly shall be provided to remove oversized
objects. The unit selected shall be sized to maximize grit removal and minimize organic removal
contaminants. Detention time in the chamber shall be at least one minute at the design flow. Flow
velocities shall be between one and two feet per second at the design flow. To prevent clogging,
screening unit shall be installed upstream of the cyclonic degritter.
(e) Vortex Grit Chamber. Inlet channels shall include sufficient straight length to deliver smooth
flow to the units. Vortex system shall be equipped with rotating paddles in the center of the grit chamber
and shall rotate at a maximum 21 rpm. Minimum initial inlet velocity at the 2-hr peak flow shall be at least
2.0 fps. The outlet channel should maintain a constant elevation. Grit removal from the grit storage
chamber located below the grit separation chamber shall be by pumps specifically designed to handle grit.
§217.134. Grit Handling.
The need for grit washing shall be determined by the type of grit removal system and the final
means of grit disposal. Drainage for grit washing facilities and grit storage areas shall be returned to the
head of the plant. Grit chambers located below ground level shall have mechanical grit removal
equipment. Grit shall be stored in containers with a tight fitting cover and shall be managed and disposed
of in accordance with Chapter 330 of this title (relating to Municipal Solid Waste).
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§217.135. Preaeration Facilities.
Preaeration may be used for odor control, flocculation of solids, reducing septicity, grease
separation, and promoting uniform distribution of solids to clarifiers. Preaeration system design and sizing
will vary greatly. The basis for preaeration system designs shall be detailed in the final engineering design
report.
§217.136. Flow Measurement.
A means of accurate effluent flow measurement shall be provided at all wastewater treatment
facilities. Where average influent and effluent flows are significantly different, e.g., plants with large
water surfaces located in areas of high rainfall or evaporation, or plants using a portion of effluent for
irrigation that is not measured by the final flow metering devices, both influent and effluent shall be mea
sured. Internal flow monitoring devices, to measure returned activated sludge and/or to facilitate splitting
flows between units, shall be provided as required by other portions of this chapter. Effluent flow
measurement devices shall be of the open channel type to allow for easy inspection, calibration, and
cleaning. Flow measurement shall be by a combination of primary and secondary devices.
(1) Primary measuring devices. Primary measuring devices include weirs and flumes.
A non-corrosive ruler (staff gauge), graduated in ¼-inch increments and clearly visible, shall be installed
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upstream of the primary measuring device to permit the manual measurement of water depth. The
primary devices shall be located to facilitate easy cleaning by plant personnel.
(A) Weirs. The weir shall be located to provide accurate flow rate
measurements. The channel approach section to the weir shall be straight for a distance of at least 20
times the maximum expected head on the weir. The height of the weir from the channel bottom to the
weir crest shall be a minimum of twice the maximum expected head on the weir or 1 foot, whichever is
greater. The upstream edge of the weir shall be sharp. The crest of the weir shall be exactly level to
ensure a uniform depth of flow. The upstream face of the weir shall be smooth and perpendicular to the
axis of the channel in both the horizontal and vertical directions. The flow measurement device
(secondary measuring device) shall be placed upstream from the the weir, a minimum distance of 3 times
the maximum expected head on the weir, or as recommended by the equipment manufacturer.
(B) Flumes. Flumes shall be located in straight sections of an open channel.
Flumes shall be installed in accordance with manufacturer’s recommendations. The approaching flow
shall be distributed evenly across the flow channel and shall be designed to preclude turbulence and
waves.
(2) Secondary measuring devices. Secondary measuring devices shall measure the liquid
level in the primary measuring device, and shall convert this liquid level into a flow rate which is integrated
to a totalized volume. Secondary measuring devices shall be installed in accordance with manufacturer’s
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recommendations. All installations shall include, within easy observation of the primary device, a display
of the instantaneous flow rate being measured and a means of reading the totalized flow.
§217.137. Flow Equalization Basins.
Flow equalization basins shall be used whenever a facility’s total daily influent flow volume occurs
during a period of time less than or equal to 10 hours of a day, for any day of any week; whenever a
facility experiences periods of time where it receives an influent flow of less than 10% of its design
capacity, for a period of time greater than or equal to 48 hours in any one week; or, at any other time the
engineer deems that flow equalization is necessary to minimize random or cyclic peaking of organic or
hydraulic loadings. Flow equalization basins shall be preceded by a coarse screening device. The
engineer shall consider the necessity for grit removal prior to flow equalization.
(1) Aeration. Aeration of the flow equalization basin is required. The aeration system
shall be sized to maintain a dissolved oxygen level of at least 1.0 mg/l in the equalization basin at all times.
(2) Mixing. Mixing shall be provided which is sufficient to prevent solids deposition in
the basin. Mixing shall be provided by mixing equipment, a diffused aeration system, or a mechanical
aeration system.
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(3) Volume. Sizing of the flow equalization basin shall be based on diurnal flow variation
and downstream process unit sizing and capabilities. Calculations justifying the sizing of the flow
equalization basin shall be included in the final engineering design report. The feasibility of using multiple
compartments shall be considered by the engineer to allow for operational flexibility, repair and cleaning.
(4) Pumped flow. For pumped flow to an equalization basin, the effluent from the basin
shall be controlled by a flow-regulating device capable of maintaining the flow rate within an acceptable
range for downstream process units. For pumped flow from the equalization basin, variable-speed pumps,
or multiple pumps are required in order to deliver a constant flow to downstream process units.
§217.138. Primary Clarifiers. - Design Basis.
(a) Inlets. Clarifier inlets shall be designed to provide uniform flow and stilling. Vertical flow
velocity through the inlet stilling well shall not exceed 0.15 feet per second at peak flow. Inlet distribution
channels shall not have dead-end corners and shall be designed to prevent the settling of solids in the
channels. Inlet structures shall be designed to allow floating material to enter the clarifier.
(b) Scum removal. Scum baffles and a means for the collection and disposal of scum shall be
provided for primary clarifiers. Scum from primary clarifiers shall be discharged to a sludge digester or
other approved method of disposal. DISCHARGE OF SCUM TO ANY OPEN DRYING AREA IS PROHIBITED.
Mechanical skimmer shall be used in units with a design flow greater than 25,000 gallons per day.
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Smaller systems may use hydraulic differential skimming provided that the scum pickup is capable of
removing scum from the entire operating surface of the clarifier. Scum pumps shall be specifically
designed for this purpose.
(c) Effluent weirs. Effluent weirs shall be designed to prevent turbulence or localized high
vertical flow velocity in the clarifiers. Weirs shall be located to prevent short circuiting flow through the
clarifier and shall be adjustable for leveling. Based on peak flows, weir loadings shall not exceed 20,000
gallons per day per linear foot of weir length for plants with a design flow of 1.0 mgd or less. Weir
loadings for plants with a design flow in excess of 1.0 mgd shall not exceed 30,000 gallons per day peak
flow per linear foot of weir.
(d) Basin sizing. Overflow rates are based on the surface area of the clarifiers. The surface
areas required shall be computed using the following criteria. The actual clarifier size shall be based on
whichever is the larger size from the two surface area calculations (based on peak flow and design flow
surface loading rates). The following design criteria for primary clarifiers are based upon a minimum side
water depth of 10 feet and shall be considered acceptable:
(1) Maximum Surface Loadinga @ Peak Flow = 1800 gal/day/ft2
(2) Maximum Surface Loadinga @ Design Flow= 1000 gal/day/ft2
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(3) Minimum Effective Detention Timeb @ Peak Flow = 0.9 hrs
(4) Minimum Effective Detention Timeb @ Design Flow = 1.8 hrs
(A) Does not include recirculation flow.
(B) Overflow rate and side water depth (SWD) may be adjusted, keeping the
detention time unchanged, over a range of 10 to 18 feet of SWD. The detention time is based on the
effective volume and the overflow rate of the circular or rectangular clarifier. (The effective volume
includes all liquid above the sludge blanket.) For cone bottom tanks, the top of the sludge blanket is
considered to be at the top of the cone. For flat bottom tanks, a sludge blanket of 3 feet shall be allowed
for development of maximum return sludge concentration.
(e) Sidewater depth. The minimum sidewater depth for primary clarifiers is 10 feet.
(f) Freeboard. Walls of primary clarifiers shall extend at least 6 inches above the surrounding
ground surface and shall provide not less than 12 inches freeboard at peak flow.
(g) Drains. Provisions shall be made for complete dewatering of each primary clarifier unit to an
appropriate point in the treatment facility. Portable dewatering pumps are considered acceptable for
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complete dewatering. Devices such as hydrostatic relief valves to prevent flotation of structures shall be
considered.
(h) Accessiblity. All primary clarifiers shall be designed to facilitate routine operation and
maintenance.
(i) Primary Clarifiers - BOD5 Removal. The assumed BOD5 reduction in a primary clarifier is
35 percent, unless satisfactory evidence is presented to indicate that the efficiency will be otherwise.
(j) Primary Clarifiers - Sludge Pumping and Piping. All primary clarifier units shall be provided
with mechanical sludge collection equipment designed to assure rapid removal of the sludge. Means for
transfer of sludge from primary clarifiers for subsequent processing shall be provided so that treatment
efficiency will not be adversely affected. Gravity sludge transfer lines shall not be less than eight inches
in diameter.
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SUBCHAPTER F : ACTIVATED SLUDGE SYSTEMS
§§217.150-217.164
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code as well as the authority to set standards to prevent the
discharge of waste that is injurious to the public health under §26.041 of the Texas Water Code.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.150. Applicability.
This subchapter provides the design requirements for activated sludge systems. Systems may be
designed using a traditional design approach which involves sizing the aeration basin and clarifier based on
values which have been used historically as standard engineering practice, or, the systems may be
designed using a volume-flux approach which involves sizing the aeration basin and clarifiers based on the
relationship between the volume flux of solids in the secondary clarifier, the sludge volume index, and the
sludge blanket depth.
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§217.151. General Requirements for Activated Sludge Aeration Basins.
(a) Minimum Dissolved Oxygen Concentration in Aeration Basins. Aeration Systems shall be
designed to maintain a minimum dissolved oxygen concentration of 2.0 mg/l throughout the basin at the
maximum diurnal organic loading rate determined in §217.32(3) or §217. 33(2)of this title (relating to
Design of New System - Organic Loading Flows, Design of Existing System - Organic Loading and
Flows, and Table B.1).
(b) Alternate Aeration Volume. The volume in aerated influent wastewater channels and
aerated mixed liquor transfer channels may be used to meet aeration basin volume requirements, provided
the aeration is by diffused air, and the diffuser depth conforms to the requirements of §217.156(b)(5)(A)
of this title (relating to Aeration Equipment Sizing.)
(c) THE USE OF CONTACT STABILIZATION SYSTEMS FOR NITRIFICATION IS PROHIBITED.
§217.152. General Requirements for Activated Sludge Clarifiers.
(a) Inlets. Inlet valves or gates shall be provided for all clarifiers. Clarifier inlets shall be
designed to provide uniform flow and stilling. Precautions shall be taken to ensure that air is not trapped
or entrained in the transfer piping. Vertical flow velocity through the inlet stilling well shall not exceed
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0.15 feet per second at peak flow. Inlet distribution channels shall be designed to prevent the settling of
solids in the channels.
(b) Scum removal. Scum baffles and a means for the collection and disposal of scum shall be
provided for all clarifiers. Scum collected from clarifiers in plants utilizing the activated sludge process
and aerated lagoons may be discharged to aeration basin(s) and/or digester or disposed of by other
approved methods. Scum from all other clarifiers shall be discharged to the sludge digester or disposed of
in a manner which complies with Chapter 312 of this title (relating to Sludge Use, Transportation and
Disposal). Discharge of scum to any open drying area is not acceptable. Mechanical skimmer shall be
used in units with a design flow equal to or greater than 10,000 gallons per day. Smaller systems may use
hydraulic differential skimming provided that the scum pickup is capable of removing scum from the entire
operating surface of the clarifier. Scum pumps shall be specifically designed to pump scum.
(c) Effluent weirs. Effluent weirs shall be designed to prevent turbulence or a localized high
vertical flow velocity in the clarifiers. Weirs shall be located a minimum of six inches (horizontally) from
an outer wall or baffle. Weirs shall be located to prevent the short circuiting of flow through the clarifier.
Weirs shall be adjustable such that the water surface elevation in the clarifier may be raised and lowered
if needed. Weir loadings shall not exceed 20,000 gallons per day at the two-hour peak flow per linear foot
of weir length for plants with a design flow of less than 1.0 mgd. Special consideration will be given to
weir loadings for plants with a design flow equal to or greater than 1.0 mgd, but such loadings shall not
exceed 30,000 gallons per day two-hour peak flow per linear foot of weir. Circular clarifiers with
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peripheral overflow weirs shall have weirs around the entire perimeter of the clarifier. Circular clarifiers
with full perimeter weirs are not limited to the weir overflow rates as listed in this subsection.
(d) Sludge Lines. Means for transfer of sludge from clarifiers for subsequent processing shall be
provided so that treatment efficiency will not be adversely affected. Sludge lines shall be a minimum of
four inches in diameter to reduce the chances of clogging due to debris in the wastewater. In addition, the
flow velocity in the sludge line shall be greater than two feet per second to prevent deposition.
(e) Sludge Collection Equipment. All clarifier units that treat flow from a treatment plant facility
with a design flow of 10,000 gallons per day or greater shall be provided with mechanical sludge collecting
equipment.
(f) Pumped Inflow. For wastewater treatment systems with pumped inflow, clarifiers shall have
adequate capacity for two-hour peak flow or "firm pumping capacity." This flow rate may also include
skimmer flow, thickener overflow, filter backwash, and similar considerations. All treatment plants shall
be designed to hydraulically accommodate peak flows without adversely affecting the treatment pro
cesses.
(g) Side Water Depth (SWD). The SWD is defined as the water depth from the top of the cone
in cone bottom tanks, or from 2 feet above the bottom in flat bottom tanks with a hydraulic sludge removal
mechanism to the water surface. All clarifiers with mechanical sludge collectors and with surface area
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greater than 300 ft2 shall have a minimum SWD of 10 feet. All clarifiers with a surface area less than
300 ft2 shall have a minimum SWD of 8 feet. The SWD for hopper bottom clarifiers shall be computed
using equation 1.f. The side water depth computed using equation 1.f excludes the hopper portion of the
clarifier. The upper third of the hopper portion of the hopper bottom clarifier may be counted as part of
the SWD only if the surface area of the hopper bottom clarifier is increased by 15% over the surface
area determined from the design surface loading calculated using Table F.2, and if the activated sludge
plant includes a flow equalization basin. The SWD of a hopper bottom clarifier shall never be less than 5
feet. Figure 1: §217.152(g)
SWD=160*Q+4 Equation 1.f
Where: SWD = side water depth required (ft)
Q = annual average flow in MGD as determined in §217.31(a)
(h) Restrictions on Hopper Bottom Clarifiers. Hopper bottom clarifiers without mechanical
sludge collection equipment shall not be used for facilities with a maximum flow greater than 10,000
gallons per day. When hopper bottom clarifiers are used, each hopper shall have individually-controlled
sludge removal. Hopper bottom clarifiers shall have a smooth wall finish and an upper hopper slope of
not less than 60 degrees measured from the horizontal.
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(i) Short Circuiting. The influent stilling baffle and effluent weir shall be designed to prevent
short circuiting.
(j) Return Sludge Pumping Capacity. The capacity of return sludge pumping units shall be
calculated on the basis of the area of the activated sludge clarifiers, and the pumping capacity is
designated as the clarifier underflow rate in gallons per day per square foot. The maximum underflow
rate shall be 400 gpd/sf. Through throttling, variable speed, or multiple pumps, control ability shall be
provided to operate over the range of 200 gpd/sf to 400 gpd/sf.
§217.153. General Requirements Which Apply to both Aeration Basins and Clarifiers.
(a) Construction of Aeration Basins and Clarifiers. Aeration basins and clarifiers shall be
constructed of materials which are designed to resist the effects of corrosive sewage environments.
(b) Freeboard. All aeration basins shall have a minimum freeboard of 18 inches at the two hour
peak flow. All clarifiers shall have a minimum freeboard of 1 foot at the two hour peak flow.
(c) Flow Splitting. For all new installations which propose a design flow of greater than or equal
to 0.4 mgd, a minimum of two aeration basins and two clarifiers shall be provided. The piping shall be
designed to be capable of hydraulically passing the two hour peak flow with either the largest clarifier or
the largest aeration basin out of service. The individual aeration basins and clarifiers shall have gates or
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valves to allow them to be hydraulically isolated. All aeration basins and clarifiers shall have a dedicated
means for dewatering. The flow into and out of the clarifiers shall not be allowed to short circuit.
§217.154. Aeration Basin and Clarifier Sizing - Traditional Design Approach.
This section provides the standard design values which shall be used to size aeration basins and
clarifiers when using traditional design approaches.
(1) Aeration Basin Sizing. The aeration reactor shall be sized using the organic loads
calculated in §217.32(3) or §217.33(2) of this title (relating to Design of New Systems - Organic Loadings
and Flow and Design of Existing Systems - Organic Loadings and Flow). Based on these organic loads,
the aeration basin volume shall be sufficient to ensure that the organic loading on the aeration basins do
not exceed the rates in Table F.1. For purposes of design, the reactor temperature shall be assumed to be
equivalent to the average of the lowest conserctuive seven-day mean reactor temperature from a similar
facility located within 50 miles of the subject site. Figure 1: §217.154(1)
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Table F.1 - Design Organic Loading Rates for Sizing Aeration Basins Based on Traditional Design
Methods
Process Applicable Permit Effluent Sets
BOD5/TSS/Ammonia Nitrogen
Maximum Organic Loading
Rates lbs BOD5/day/1,000 cf
Conventional Activated Sludge
Process Without Nitrification
10/15 or 20/20 45
Conventional Activated Sludge
Process With Nitrification When
Reactor Temperatures Exceed
15 degrees C
10/15/3,2, or 1 35
Conventional Activated Sludge
Process With Nitrification When
Reactor Temperatures are 13 to
15 degrees C
10/15/3,2, or 1 25
Conventional Activated Sludge
Process With Nitrification When
Reactor Temperatures are 10 to
12 degrees C
10/15/3,2, or 1 20
Extended Aeration Basins
Including Oxidation Ditches
(MCRT over 20 days)
10/15/3,2, or 1 15
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(2) Clarifier Sizing. Table F.2 details the maximum surface loading rates and the
minimum detention times which shall be used to determine the size of activated sludge clarifiers. The
clarifier shall meet both the detention time and overflow rate criteria. When calculating overflow rates
for proposed clarifiers, sludge recycle flow shall not be included for purposes of determining compliance
with Table F.2. Also, when calculating the overflow rate for a proposed clarifier, the surface area of the
stilling well shall be included as part of the clarifier surface area. Figure 2: §217.154(2)
Table F.2 - Maximum Clarifier Overflow Rates (based upon traditional design methods)
Permit
Limits
Aeration Basin
Organic Loading
(lbs
CBOD5/day/1000
cf) (from Table
F.1)
Process - Treatment
Level
Maximum
overflow rate at
2-Hour Peak
Flow (gal/day/sf)
Minimum
Detention Time
at 2-Hour Peak
Flow (hrs)
20/20 or
10/15
45 Fixed Film - Secondary
or Enhanced
Secondary
1200 1.8
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20/20,
10/15, or
10/15/3
45, 35, 25 or 20 Activated Sludge
Secondary, Enhanced
Secondary, or
Secondary with
Nitrification
1200 1.8
20/20 15 Extended Air
Secondary
900 2.0
10/15/3 15 Extended Aeration
Enhanced Secondary
800 2.2
§217.155. Aeration Basin and Clarifier Sizing - Volume-Flux Design Approach.
This design approach is offered as an alternative to the traditional design approach. The design
method for this approach is located in Appendix I of this subchapter. This method is restricted to facilities
with a design flow greater than 0.40 mgd.
§217.156. Aeration Equipment Sizing.
(a) Oxygen Requirements (O2R) of the Wastewater. Mechanical and diffused aeration systems
shall be designed to provide sufficient dissolved oxygen to the wastewater to meet the demands of the
aeration basin. Aeration systems shall be designed to provide a minimum dissolved oxygen concentration
in the aeration basin of 2.0 mg/l. Mechanical and diffused aeration systems shall be designed to supply
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the O2R calculated by equation 2.f or use the recommended values presented in Table F.3. These O2R
were calculated using concentrations of 200 mg/l BOD5 and 45 mg/l NH3-N in equation 2.f. Figure 1:
§217.156(a)
O2R=[1.2(BOD5)+4.3(NH3-N)]/(BOD5) Equation 2.f
Table F.3 - Minimum O2R
Process O2R, lbs O2/lb BOD5
Conventional Activated Sludge Systems
which are not Intended to Nitrify
1.2
Conventional Activated Sludge Systems
which are Intended to Nitrify; and, Extended
Aeration Systems (including all Oxidation
Ditch Treatment Systems)
2.2
(b) Diffused Aeration Systems.
(1) Design Air Flow Requirements - Default Values. Table F.4 may be used to
determine the air flow for which the diffused air systems shall be sized. The values in Table F.4 were
developed using equation 4.f with the following assumptions: a transfer efficiency of 4.0 percent in
wastewater for all diffused air activated sludge processes; a diffuser submergence of 12 feet; a
wastewater temperature of 20E C; and the oxygen requirements in Table F.3. Figure 2: §217.156(b)(1)
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Table F.4 - Minimum Air Flow Requirements for Diffused Air
Process Air Flow/BOD5 load, standard cubic
feet (SCF)/day/lb BOD5
Conventional Activated Sludge Systems
which are not Intended to Nitrify
1800
Conventional Activated Sludge Systems
which are Intended to Nitrify; and, Extended
Aeration Systems
3200
(2) Design Air Flow Requirements - Equipment and Site Specific Values. When the
default values in paragraph (1) of this subsection are not used, the air flow requirements for the diffused
air equipment shall be calculated in accordance with subparagraphs (A)-(D) of this paragraph.
(A) Determine Clean Water Oxygen Transfer Efficiency (CWOTE). Clean
water oxygen transfer efficiencies greater than 4% may be used provided that full scale diffuser perfor
mance data from a certified testing laboratory, or sealed by an independent licensed professional engineer
is presented which demonstrates the diffusers’ transfer efficiencies. The testing laboratory or licensed
engineer shall utilize the oxygen transfer testing methodology described in the ASCE publication entitled,
“A Standard for the Measurement of Oxygen Transfer in Clean Water” (1984). Diffuser systems which
claim a clean water transfer efficiency greater than 18% for coarse bubble systems and greater than 26%
for fine bubble systems shall be considered innovative technologies by the executive director, and will be
subject to §217.10(b) of this title (relating to Approvals of Innovative and Nonconforming Technologies)
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at the executive director’s discretion. Clean water transfer efficiencies obtained at temperatures other
than 20 degrees Celsius shall be adjusted to reflect approximate transfer efficiencies and air requirements
under field conditions by use of equation 3.f. Figure 3: §217.156(b)(2)(A)
FTE’ (Te)( (WOTE/CWOTE)(1.024T&20( (Cf/Ct) Equation 3.f
Where:
Te = Test Efficiency
FTE = Field Transfer Efficiency (decimal)
WOTE = Wastewater Oxygen Transfer Efficiency (decimal)
CWOTE = Clean Water Oxygen Transfer Efficiency (decimal)
T = Temperature (degrees C)
Cf = Oxygen Saturation in Field (Includes temperature,
dissolved solids, pressure etc.)
Ct = Oxygen Saturation in Test Conditions
(B) Determine Wastewater Oxygen Transfer Efficiency (WOTE). The
wastewater oxygen transfer efficiency shall be estimated from clean water test data by multiplying the
clean water transfer efficiency by 0.65 for coarse bubble diffusers and by multiplying the clean water
transfer efficiency by 0.45 for fine bubble diffusers. Plants treating greater than 10 percent industrial
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wastes shall provide additional testing and data, including pilot studies when requested by the executive
director, to justify actual wastewater transfer efficiencies.
(C) Determining Required Air Flow (RAF) Rate. Equation 4.f shall be used to
calculate the air flow rate for which the diffuser system shall be sized for a 12-foot diffuser submergence.
If the diffuser submergence is other than 12 feet, the RAF shall be corrected as detailed in subparagraph
D of this paragraph. Figure 4: §217.156(b)(2)(C)
RAF’ [(PPD BOD5)( (O2/lb BOD5)]/[WOTE(0.23(0.075(1440] Equation 4.f
Where:
RAF = Required Air Flowrate (SCFM)
PPD CBOD5 = Influent Organic Load in Pounds per Day
0.23 = lb 02/lb air @ 20 degrees C
1440 = minutes/day
0.075 = lb air/(cubic foot)*
WOTE = Wastewater Oxygen Transfer Efficiency (decimal)
* If the design inlet temperature is above 24 degrees C, the specific weight of
air shall be adjusted to the specific weight at the intake temperature.
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(D) Corrections to RAF Rate Based on Varying Diffuser Submergence Depths.
If a diffuser submergence differing from 12 feet is proposed, the minimum air flow rate calculated in
subparagraph (C) of this paragraph shall be adjusted by multiplying the calculated values by the factors in
Table F.5. Figure 4: §217.156(b)(2)(D)
Table F.5 - Diffuser Submergence Correction Factors
Diffuser Submergence Depth (ft) Air Flow Rate Correction Factor
8 1.82
10 1.56
12 1.00
15 0.91
18 0.73
20 0.64
(3) Mixing Requirements for Diffused Air. Air requirements for mixing shall be
calculated along with those required for the design organic loading. (The designer may use to Chapter 11
of Design of Municipal Wastewater Treatment Plants, a joint publication of the American Society of
Civil Engineers and the Water Environment Federation, for mixing requirements.) Air input for mixing
shall be greater than or equal to 20 SCFM/1000 cf for coarse bubble diffusers and greater than or equal to
0.12 SCFM per square foot for fine bubble diffusers.
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(4) Blowers and Air Compressors. Blowers and compressors shall be of such capacity
to provide the required aeration rate as well as the requirements of all supplemental units such as airlift
pumps. Blower or compressor calculations shall be included in the final engineering design report which
show the actual air requirements for the expected temperature range (both summer and winter conditions)
and the impact of the actual site elevation on the air supply. Multiple compressor units shall be provided
and shall be arranged so the capacity of the total air supply is adjustable to meet the variable organic load
to be placed on the treatment facility. The compressors shall be designed so that the maximum design air
requirements may be met with the largest single unit out of service. The blower/compressor units shall
automatically restart after a period of power outage, or the operator or owner shall be notified by some
method such as telemetry or an auto-dialer. The specified capacity of the blowers or air compressors,
particularly centrifugal blowers, shall take the following into account: the air intake temperature may
reach 100 degrees F (38 degrees C) or higher, and the pressure may be less than standard (14.7 pounds
per square inch absolute). The capacity of the motor drive shall also take into account that the intake air
may be 20 degrees F (-7 degrees C) or less and may require over sizing of the motor, or a means of
reducing the rate of air delivery, to prevent overheating or damage to the motor.
(5) Diffuser Systems - Additional Requirements.
(A) Diffuser Submergence. Submergence depths for diffusers shall not be less
than the depths in Table F.6 for new plants. For additions to existing plants, diffuser submergence depths
may be adjusted to match existing air pressure, delivery rate, and hydraulic requirements. DIFFUSER
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SUBMERGENCE DEPTHS OF LESS THAN 7 FEET ARE PROHIBITED. Figure 6:
§217.156(b)(5)(A)
Table F.6 - Minimum Diffuser Submergence Depth
Design Flow, mgd Minimum Submergence Depth, feet
0.01 or less 8.0
0.01 to 0.10 9.0
Greater than 0.10 10.0
(B) Grit Removal. Systems which utilize fine bubble diffusers and have
wastewater which has high concentrations of grit shall either provide a grit removal unit upstream of the
aeration process or shall have multiple trains which may be taken out of service and are provided with a
means to achieve grit removal.
(C) Aeration System Piping. Each diffuser header shall include a control valve.
These valves are basically for open/close operation, but the use of a throttling type valve shall be
considered. Valves shall be designed to withstand the heat of the compressed air. Air headers shall be
designed to withstand temperatures up to 250 degree F. The air diffuser system, including piping and
diffusers, shall be capable of delivering 150 percent of design air requirements. The aeration system
piping shall be designed to minimize head losses. A hydraulic analysis of the entire air piping system shall
be included in the final engineering design report which quantifies head loss through the piping system and
which details the distribution of air from the blowers to the diffusers. The air hydraulic profile shall
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demonstrate that the air system is capable of delivering sufficient air to the aeration basin to supply the air
demands required by this section. The use of non-metallic piping for the aeration system shall be
restricted to use in the aeration basin only, and shall be a minimum of four feet below the average water
surface elevation in the aeration basin.
(c) Mechanical Aeration Systems.
(1) Required Air Flow - Default Values. This chapter does not provide default values
for mechanical aeration systems.
(2) Required Air Flow - Equipment and Site Specific Values. The air flow requirements
for which mechanical systems shall be designed shall be calculated in accordance with subparagraphs (A)
and (B) of this paragraph.
(A) Determine Clean Water Oxygen Transfer Efficiency. Clean water oxygen
transfer rates shall be less than or equal to 2.0 pounds of oxygen per horsepower-hour. Materials such as
performance curves, which detail the oxygen transfer rates of mechanical equipment, shall be included in
the final engineering design report. Proposed clean water transfer rates in excess of 2.0 pounds of
oxygen per horsepower-hour shall be justified by full scale performance data conducted by a certified
testing laboratory, or sealed by an independent, licensed professional engineer. The testing laboratory or
licensed engineer shall utilize the oxygen transfer testing methodology described in the ASCE publication
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entitled, “A Standard for the Measurement of Oxygen Transfer in Clean Water” (1984). Mechanical
equipment with proposed clean water transfer efficiencies in excess of 2.0 pounds of oxygen per
horsepower-hour shall be considered innovative technologies by the executive director and are subject to
the requirements of §217.10(b) of this title (relating to Approvals of Innovative and Nonconforming
Technologies).
(B) Determine Wastewater Oxygen Transfer Efficiency. The wastewater
transfer efficiency shall be estimated from the clean water transfer efficiency by multiplying the clean
water transfer efficiency by 0.65 for all mechanical aeration equipment. Plants treating greater than 10
percent industrial wastes shall provide data to justify actual wastewater transfer efficiencies.
(3) Mixing Requirements. In addition to providing sufficient oxygen transfer capability
for satisfying oxygen requirements, the mechanical aeration devices shall also be required to provide
sufficient mixing to prevent deposition of mixed liquor suspended solids (MLSS) under any flow
conditions. The mechanical aeration devices shall also be capable of re-suspending the MLSS after a
shutdown period caused by power outage or outage for maintenance purposes. A minimum of 100
horsepower per million gallons of aeration basin volume, or 0.75 horsepower per 1000 cubic feet of
aeration basin volume, shall be furnished for channel or basin type layouts.
(4) Mechanical Components.
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(A) Process reliability. A minimum of two mechanical aeration devices shall be
provided in each basin. The mechanical aeration devices shall be designed so that the maximum design
oxygen transfer requirements may be met with the largest single unit out of service. The mechanical
aeration devices shall automatically restart after a period of power outage or the operator or owner shall
be notified by some method such as telemetry or an auto-dialer.
(B) Operations and maintenance. Two speed or variable speed drive units shall
be used. Single speed units with timer controlled operation may be used if an independent means of mixing
is used. Bearings, drive motors, and gear reducers (if utilized) shall be operator accessible. Bearings,
drive motors, and gear reducers (if utilized) shall contain splash shields or other types of splash prevention
devices, such that routine maintenance can be performed on the components without the danger of the
plant operator being exposed to contact with raw or partially- treated sewage. Where gear reducers are
employed in the mechanical aerator design, adequate means for draining the gear reducer shall be
provided such that the operator does not come in contact with mixed liquor. If a hand pump is required to
drain the gear reducer, then the pump device shall be furnished with the mechanical aeration equipment.
§217.157. Sequencing Batch Reactors (SBR).
(a) System Sizing and Reliability. In general, system reliability shall be in accordance with
§217.156(b) and §217.156(c)(3) of this title(relating to Aeration Equipment Sizing). Power source
reliability shall be in accordance with §217.35 of this title (relating to Backup Power Requirements). At a
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minimum, the decantable volume of the SBR system, with the largest basin out of service, shall be sized to
pass the design flow on a continuous basis without changing cycle times. Aerated storage of mixed liquor
shall be provided separate from the SBR tank(s) to accommodate basin down times for all two-basin
treatment plants without removable aeration devices. Systems with fixed level decanters shall provide
more than two basins and additional decantable storage volume to account for the added settling time
before a discharge may occur. Equalization basins shall be considered for all SBR plants, and shall be
required for all SBR plants with fixed decant equipment where decant volumes do not accommodate the
design flow. Organic space loadings shall conform to §217.154(1) Table F.1 of this title (relating to
Aeration Basin and Clarifier Sizing- Traditional Design Approach). Maximum space loadings shall be
kept below 35 pounds of CBOD5 per 1,000 cubic feet of tank volume. The reactor MLSS level at the low
water level (normal operating level) shall be in the range of 3,000 mg/l to 5,000 mg/l. The depth of the
REACT volume shall not be less than 9 feet. The minimum side water depth of the tanks shall be 12 feet
or more. Sludge digestion shall be provided pursuant to the requirements in Subchapter J of chapter.
(b) Decanter Design.
(1) Velocities at the inlet port or at the edge of submerged weirs shall be designed to
eliminate vortexing, disturbance of the settled sludge, or entry of floating materials. The entrance velocity
to the decanter shall not exceed 1.0 feet per second. The decanter shall draw effluent from below the
water surface, and a device which excludes scum shall be provided. An adequate zone of separation
between the settled sludge and the decanter height shall be maintained, but in no case shall this distance
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be less than 12 inches. Decanters shall be provided with a means of excluding solids from entering the
decanter during the REACT cycle. Some available mechanisms include the following:
(A) recycle treated effluent to wash out solids trapped in the decanter;
(B) physically remove a decanter from the mixed liquor except during decanting;
(C) mechanically close the decanter when it is not in use; or
(D) fill the decanter with air except during the decant period.
(2) The decanter and related piping and valves shall be protected from freezing and ice
buildup. Floating or movable decanters are recommended over fixed decanters. Fixed decanters shall not
be used in basins where simultaneous fill and decant may occur. The decant system, with the largest tank
out of service, shall be sized to handle the design flow without changing the cycle time. This sizing is
applicable to any system of tanks that are fed sequentially. System flexibility and outfall piping shall be
provided to allow the decant of at least two tanks simultaneously for all SBR systems utilizing more than
two basins. Downstream treatment units shall be sized to handle peak flow rates. Flow equalization
downstream of the batch reactors, to dampen the higher flow rates associated with the decanting cycle,
shall be provided in order to minimize disinfection basin volume and size of disinfection equipment unless
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those downstream units and the receiving stream are sufficiently capable of accepting the peak flowrate
of the decanter.
(c) Tank Details. Multiple tanks are required. Influent baffling and physical separation from the
decanter shall be provided for all SBR systems with only two tanks, or any SBR system which may
operate with a continuous feed during settling and decanting phases. Elongated tanks shall be considered
for systems where influent baffling is required. All SBR tanks shall have a minimum freeboard of not less
than 18 inches. Protection from uplift when empty shall be provided where high groundwater may occur.
Structures utilizing common walls shall be designed for a worst case condition of one basin at maximum
liquid level and the adjacent basin completely empty. All walls shall be hydrostatically sound. A means of
dewatering each tank shall be provided. A sump shall be provided in all basins with flat bottoms.
Additionally, each SBR system shall have the capability to transfer sludge from each basin to the other
aeration basins. A means of scum removal from each aeration tank shall be provided. Prevailing winds
should be considered in scum control. Each tank shall be provided with an overflow to the other aeration
tank(s) or to a storage tank. Above this level, a high water overflow from the SBR tank(s) requiring
manual activation by operating personnel shall sound an alarm and notify plant operating personnel at
plants not manned 24-hours a day as outlined in §217.161 of this title (relating to Electronics and
Instrumentation System). All SBR projects shall consider the means and frequency for removal of grit and
other debris from the SBR basins. Adequate space for equipment access (possibly cranes) shall be
considered, especially if the tanks are deep. Fine screens may be utilized pursuant to Subchapter E,
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§217.126 thru §217.130 of this title (relating to Preliminary Treatment Units). The use of communitors
shall be limited to SBR systems preceded by primary clarifiers.
(d) Aeration and Mixing Equipment. In addition to the requirements of §217.156 of this title
(relating to Aeration Equipment Sizing), aeration equipment shall be suitable for cyclical operation in a
sequencing batch reactor. The aeration and mixing equipment shall not produce flow patterns within the
aeration tank which interfere with quiescent settling. Oxygen transfer rates for the aerators, at average
water depth, during the fill cycle shall be designed to provide a residual of 2.0 mg/l D.O. in the basin.
Blower discharge pressure shall be determined at the maximum water depth. When the SBR system is
utilized for biological nutrient removal or reduction, the requirements of §217.163 of this title (relating to
Advanced Nutrient Removal) shall be used in the design. Provisions for the removal of air diffusers or
mechanical aeration devices without dewatering the tank shall be included. If aeration equipment cannot
be maintained without dewatering the tank, a minimum of four SBR tanks shall be provided.
(e) Electrical and Controls. The motor control center (MCC) should be located for convenient
operation of the facility. A location in close proximity to the process, with a view of the batch reactors is
strongly recommended. Programmable logic controllers (PLC) with limited operator adjustment shall be
provided and programmed to meet the required effluent limitations for the design loadings. A hard-wired
backup means of operating the plant shall be provided should the PLC fail. Battery backup of the PLC
shall be provided. In addition, a spare set of all circuit boards shall be provided to the plant at startup. In
the plant design, the engineer shall consider the diurnal variations affection on flow and organic loading for
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each cycle. Adequate controls for the separate operation of each reactor tank shall be provided. Tank
level systems shall employ floats or pressure transducers. Float systems shall be shielded from prevailing
winds and protected from freezing. Bubbler systems shall not be used for level systems (these systems
are not reliable in mixed liquor environments).
(1) Recommended list of control panel switches.
(A) Pumps - Hand/Off/ Automatic.
(B) Valves - Open/Closed/Auto.
(C) Blowers or Aerators - Hand/Off/Automatic.
(D) Selector switch for tank(s) in operation/standby.
(2) Recommended visual displays.
(A) Mimic diagram of the process showing status of pumps, valves (including
position), blowers or aerators, and mixers (if utilized).
(B) Process cycle and time remaining.
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(C) Instantaneous and totalized flow to the plant and discharge.
(D) Tank level gauges or display of levels.
(E) Sludge pumping rate and duration.
(F) Air flow rate and totalizer.
(3) Required alarm condition indicators for the annunciator panel.
(A) High and Low water level in each tank.
(B) Valve - failure of all automatically operated valves.
(C) Decanter - failure.
(D) Blowers (if utilized) - low pressure, high temperature, and failure.
(E) Mechanical Aerator (if utilized) - high temperature, and failure.
(F) Pump - high pressure and failure.
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(G) Mixers (if utilized) - failure.
§217.158. Solids Management.
(a) Solids Recycling and Monitoring. The return sludge system shall be capable of operating
satisfactorily within anticipated flow conditions including wet weather peak flows and dry weather flows.
The monitoring and control system shall provide a means to control return and waste sludge flows from
each clarifier, to control return sludge flows into each aeration basin, to meter return sludge flows, and to
measure waste sludge flows.
(b) Solids Wasting/Solids Blanket. The design shall include adequate downstream process
capacity (such as storage, stabilization, dewatering, or disposal) such that adequate solids removal rates
may be maintained.
(c) Return Activated Sludge (RAS) Pump Design. Centrifugal sludge pumps shall have a
positive suction head unless the pumps are self-priming. If airlift pumps are used, provisions shall be
included for cleaning the pumps without removal from the basin. Sufficient pumping units shall be
provided to maintain the maximum design return pumping rate with the largest single pumping unit out of
service.
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(d) Waste Activated Sludge (WAS) Pump Design. If the design uses pumps for waste activated
sludge, at least two pumping units shall be provided. Sufficient pumping units shall be provided to prevent
excessive solids storage within clarifiers that could impair clarifier operation.
(e) Piping. The design of the sludge piping system shall provide adequate provisions for cleaning
and flushing. The design shall provide a pipe line velocity of at least 3 ft/sec. at the maximum
waste/return rate to prevent solids settlement and to provide scouring at anticipated normal operating
conditions. The sludge pipe system shall have a minimum nominal diameter of four inches.
§217.159. Process Control.
(a) Solids Retention Time (SRT) Control. The plant shall be designed with the necessary
equipment for the operator to control the SRT in the aeration tanks by wasting a measured volume of
surplus activated sludge regularly (at least weekly) from either the mixed liquor tank, a sludge re-aeration
tank, or from the return sludge. Wasting mixed liquor usually requires a thickener as part of the sludge
management process. Formulas for determining the SRT shall be presented in the Final Engineering
Design Report and included in the operating manual. The SRT required for nitrification applies to the
aerobic portion of the plant.
(b) Aeration System Control. Aeration control involves the total air supplied and the distribution
of air to the aeration tanks. In order to conserve energy, the design may provide the ability to adjust the
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airflow in proportion to the load demand of the plant. If this type of control is installed in the process,
aeration equipment shall be easily adjustable in increments and shall maintain solids in suspension within
these limits.
§217.160. Operability and Maintenance Considerations.
(a) Temperature. Equipment shall be designed to operate at the temperature extremes of the
plant location. If necessary, enclosures shall be provided to allow operation of the equipment at all times.
(b) Maintenance. Buildings that house equipment shall have adequate means to position the
equipment for removal for repair and for reinstallation. This ability may be by overhead lifting eyes to
mount a portable hoist, by overhead cranes, or by adequate building openings to allow access of truck
mounted or other lifting equipment.
§217.161. Electrical and Instrumentation Systems.
All three-phase motors shall have protection against a single-phase electrical condition. Electrical
power supplies to instrumentation and monitoring equipment shall have protection from power surges.
Optical isolation shall be considered for low voltage signal circuits to remote instruments. All plants shall
have fault monitoring and reporting. For plants that are not staffed 24 hours per day, reporting shall be to
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a location that may alert a responsible person. Faults to be monitored include the following: high wet well,
power interruption, disinfection failure, blower failure, and return sludge pumping failure.
§217.162. Flow Measurement.
Plants having a wet month design flow greater than 400,000 gpd shall provide process control
measurement at strategic operational control points: return sludge of each clarifier, waste sludge flow,
and effluent flow.
§217.163. Advanced Nutrient Removal.
Designs which anticipate advanced nutrient removal shall be considered Innovative and/or
Nonconforming technology and shall comply with §217.10(b) of this title (relating to Innovative and
Nonconforming Technology).
§217.164. Appendix I.
This design approach is offered as an alternative to the traditional design approach. The aeration
tank volume and the clarifier volume are determined by selecting a mixed liquor suspended solids and floc
volume (at SVI = 100) for the required minimum solids retention time. Larger values of mixed liquor
suspended solids require less aeration tank volume and greater clarifier volume. By examining a range of
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values of the mixed liquor suspended solids and the floc volume, the engineer may select the most
favorable arrangement for the project. When using the volume-flux design method, sizing of aeration
basins and clarifiers shall be done in accordance with the requirements of this section. This method is
restricted to facilities with design flows greater than 0.40 mgd. Figure 1:§217.164
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APPENDIX I : Volume-Flux Design Approach.
(a) Design approach.
(1) Determine the solids retention time (SRT) required to meet the permit requirement
for effluent CBOD and ammonia-nitrogen.
(2) Select a trial value mixed liquor floc volume, (for example mixed liquor suspended
solids (MLSS) at sludge volume index (SVI) of 100.
(3) Using the design organic loading rate, the required SRT and yield, and the trial
MLSS, determine the aeration tank volume.
(4) Using the trial value of mixed liquor flow volume, determine the clarifier area.
(5) For clarifiers overloaded in thickening at two hour peak flow, determine the final
MLSS during storm flow and the resulting sludge blanket depth.
(6) Observing limitations, determine the side water depth (SWD) and volume of the
clarifier.
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(7) Repeat the items described 2 through 6 of this subsection at different mixed liquor
floc volumes and select the most favorable conditions for the plant design.
(b) Aeration Basin Sizing.
(1) For plants that do not require nitrification, the minimum SRT shall be as follows:
(A) For facilities with effluent CBOD values of 20 mg/l, the minimum SRT is 3
days;
(B) For extended aeration plants with effluent CBOD values of 20 mg/l, the
minimum SRT is 22 days;
(C) For facilities with effluent CBOD values less than 20 mg/L, the minimum
SRT is 4.5 days; and
(D) For extended aeration plants with effluent CBOD values less than 20mgl,
the minimum SRT is 25 days.
(2) For plants that require nitrification, the minimum SRT shall be based on the winter
reactor temperature as set forth in §217.154(a)of this title (relating to Aeration Basin and Clarifier Sizing
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Traditional Design Approach) and the values of SRT and net solids production, Y, as listed in Table 1.
The maximum CBOD loading for single-step plants is 50 lb. CBOD/thousand cf and for the first step of
two-step plants is 100 lb. CBOD/thousand cf.
(3) Above-ground steel or fiberglass tankage shall be considered to be 2E C lower
minimum operating temperature than systems utilizing reinforced concrete tankage. Systems shall be
designed for an MLSS concentration between 2000 and 5000 mg/l. The net solids production, Y, in Table
1 includes both coefficients for yield and endogenous respiration.
Table 1 - Effect of Temperature on SRT, Net Solids Production, and F/M Rate
Temperature, "C SRT, days Net Solids Production,
Y = .965-0.013(SRT)
F/M Rate,
#BOD/#SS/day =
1/(Y*SRT)
18 4.76 0.90 0.233
17 5.25 0.90 0.212
16 5.79 0.89 0.194
15 6.38 0.88 0.178
14 7.04 0.87 0.163
13 7.77 0.86 0.150
12 8.56 0.85 0.137
11 9.45 0.84 0.126
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10 10.42 0.83 0.116
Where: Table 1 is based on the maximum growth rate of Nitrosomonas calculated using Equation 3-14
from EPA Manuel, Nitrogen Control, EPA/625/R-93/010, Sept. 1993, p. 90, shown below as equation 1.
Max. Growth Rate ’ 0.47e 0.098(T& 15),days &1 Equation 1
The necessary SRT was calculated using equation 2 as follows:
SRT ’ SF/(Max. Growth Rate) Equation 2
SF is often referred to as a safety factor, but here it also includes the design factor for the ratio of
average to maximum diurnal ammonia loading. A value of 3.0, as recommended in the EPA manual, was
used in calculating Table 1.
Determine the Volume of the Aeration Basin. Select a trial value of MLSS. The aeration basin volume is
calculated as the maximum value from equations 3 and 4.
V ’ 1,000,000(CBODL)(Y)(SRT)/(62.4MLSS) Equation 3 a
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Va ’ 1,000(CBODL)/(maximum allowable lb CBOD/kcf) Equation 4
Where: Va = Volume of aeration basin, cubic feet
CBODL = Design CBOD load, per day
Y = yield of solids per unit CBOD removed
SRT = required solids retention time, days
MLSS = mixed liquor suspended solids, mg/L
lb CBOD/kcf = maximum CBOD load/thousand cf
(c) Clarifier Sizing. The clarifier basin sizing is based on volume flux which takes into account the
floc volume of solids entering the clarifier. Biological solids may occupy different volumes for the same
mass of solids as indicated by the SVI. Any return flows from units downstream of the clarifier, such as
flow from skimmer, thickeners and filter backwash shall be added to the design flow and two-hour peak
flow for purposes of determining overflow rates for clarifier sizing. All clarifiers shall be sized to ensure
overloading in clarification does not occur under any design condition. The settling velocity of the mixed
liquor solids shall be equal to or greater than the two-hour peak overflow rate. In addition, all clarifiers
shall be sized to preclude overloading in thickening at the design flow. The design maximum mixed liquor
floc volume shall be stated in the operating instructions.
(1) Dimensions for Clarifiers Designed for No Solids Storage (i.e., not overloaded in
thickening at the two hour peak flow).
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(A) Determine Overflow Rate and Area. When clarifiers are designed for no
solids storage, Table 2 shall be used to determine the maximum surface loading rates. The MLSS
concentration shall be the same concentration assumed for sizing the aeration basin. The underflow rate
shall be chosen by the design engineer. Using Table 2, the aeration basin MLSS concentration and a
selected underflow rate; the maximum overflow rate for the clarifier, at the two hour peak flow, may be
determined. The area of the clarifier may be determined as follows:
Ac ’ 1,000,000 Qp/0Rp Equation 5
Where: Ac = area of the clarifier(s), sq ft.
Qp = two hour peak flow, MGD
ORp = overflow rate from Table 2, gpd/sf
(B) Determine Volume of Clarifier. The volume of the clarifier shall be the
greater of the values determined from the minimum SWD or the minimum detention time.
Vc, minSWD ’ Ac(minSWD) Equation 6
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V , minDT ’ (1,000,000Qp/24)(minDT)/(7.48) Equation 7 c
Where: V = volume of the clar ifier(s), cf
Ac = area of the clarifier(s), sq ft.
minSWD = 10 ft, except as allowed in §217.152(g)
minDT = minimum detention time per Table F.2, hr
(2) Dimensions for Clarifiers Designed for Solids Storage Capabilities. When clarifiers
are designed to be overloaded in thickening at the design flow, the design shall include the ability to store
solids during peak flow events. Tables 2, 3, and 4 shall be used in the design. The process for designing
a clarifier based on this concept shall be as follows:
(A) Determine Area of the Clarifier. The area calculations shall be based on the
trial MLSS selected for the sizing of the aeration basin in paragraph (1) of this subsection. The area of the
clarifier shall be the greater of the areas determined from Table 3 for the two hour peak flow and the
area determined from Table 2 for the design flow using a selected underflow rate.
Ac,2&hr peak flow ’ 1,000,000Q
p/0R
T5 Equation 8
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Ac,max 30&day average flow ’ 1,000,000Qmx30av/0RT4 Equation 9
Where: Qmx30av = design flow (MGD)
ORT5 = overflow rate from Table 3 for selected MLSS (gpd/sf)
ORT4 = overflow rate from Table 2 for selected underflow rate and
MLSS (gpd/sf)
(B) Determine the Final MLSS as the result of the transfer of solids from the
aeration tank to the clarifier by the two hour peak flow. For a clarifier that becomes overloaded in
thickening at just above the design flow, greater rates of flow will transfer solids from the aeration tank to
the clarifier until the mixed liquor solids are reduced to the concentration that no longer causes a thickener
overload.
Using Table 4 and the selected underflow rate, the MLSS concentration at peak flow may be
determined using equation 10.
MLSSp ’ (UR
T6(RSSS
T6)/(0R
p %UR
T6) Equation 10
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Where: URT6 = Underflow rate from Table 4 (gpd/sf)
Or = Overflow rate at 2-hr peak flow (gpd/sf)p
MLSSpf =Diluted MLSS during peak flow (mg/l)
RSSSm = Maximum Return Sludge Concentration from Table 4 for the
selected UR (mg/l)
(C) Determine Depth of Sludge Blanket at Two Hour Peak Flow. The depth of
the sludge blanket is determined by the aeration basin volume, the change in MLSS, the area of the
clarifier and the concentration of the blanket solids at the selected underflow rate as shown in equation
11.
SBD ’ va(MLSSav & MLSSpf)/(A BKSS)%1.0 Equation 11 c
Where: SBD = Sludge Blanket Depth (ft)
Va = Volume of aeration basins (cu ft.)
Ac = Area of clarifier (sq ft.)
MLSSp = Diluted MLSS during peak flow (mg/l)
MLSSav = Diluted MLSS during average flow (mg/l)
BKSS = Blanket concentration from Table 4 at the selected underflow
rate (mg/l)
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1.0 = Assumed sludge blanket depth during design flow conditions
(D) Determine the SWD. The SWD of the clarifier shall be the maximum value
resulting from the following conditions:
(I) 10 ft unless a lower depth is allowed by §217.152(g),
(II) minimum detention time per Table F.2,
SWDDT ’ 0Rp(DT)/180 Equation 12
(III) 3.0 times the Sludge Blanket Depth.
(E) Determine Clarifier Volume. The volume of the clarifier is the area
multiplied by the SWD determined in subparagraph (D) of this paragraph.
Vc ’ Ac(SWD) Equation 13
Where: Vc = Volume of Clarifier, (cf)
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Ac = Area of the Clarifier, (sq ft)
SWD = Side Water Depth determined in (D) above, (ft)
(F) Formulas for Tables 2, 3, and 4 Table 3 gives overflow rates that are equal
to the settling velocity of activated sludge at various floc volume concentrations. For values less than 30
percent, the floc volume is the 30-minute settled volume in an unstirred 1-liter graduated cylinder. For
greater values, the sample should be diluted so that the settled volume is between 15 and 30 percent, and
the result multiplied by the dilution factor.
(I) For floc volume less than 40 percent,
0R ’ 5053.8(1& fv/100)3.83gpd/sf Equation 14T5
(II) For floc volume greater than 40 percent,
0R ’ 9003610(fv &2.56)gpd/sf Equation 15T5
Where: ORT5 = Settling Velocity of Table 3 (gpd/sf)
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fv = Floc Volume (percent) = SVI(MLSS)/10,000 SVI (ml/g),MLSS
(mg/L)
Table 2 and Table 4 are based on an analysis of the floc volume flux, i.e. floc
volume times settling velocity, calculated from Equations 14 and 15. Table 4 is a tabulation of the
maximum concentration of the underflow at different underflow rates. The equation for Table 4 is as
follows:
RSSSm ’ 10,170,000(UR &0.391)/SVI Equation 16
Where: RSSSm = Return Sludge Suspended Solids (mg/L)
UR = Underflow Rate (gpd/sf)
SVI = Sludge Volume Index (ml/g)
Table 2 gives the overflow rate which, along with the underflow rate and MLSS,
will produce the same floc volume flux as shown in Table 4.
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Table 2 Table 3 Allowable Clarifier Surface Loading Rates For Given Underflow Maximum Allowable Clarifier
Rates With No Provisions For Sludge Storage in the Clarifier Overflow Rate Allowed for
OR Clarifiers Which are Designed to
The Maximum Surface Loading Rate at the Design Flow for Store Solids
Clarifiers Designed to Store Solids During Peak Events SVI=100
(minimum allowable SVI)
MLSS UNDERFLOW RATE (gpd/sq.ft.)
mg/l 200 250 300 350 400
2000 1081 1218 1340 1452 1554
2100 1020 1148 1262 1366 1461
2200 965 1084 1191 1288 1377
2300 914 1026 1126 1217 1299
2400 868 973 1067 1151 1229
2500 825 924 1012 1091 1163
2600 786 879 962 1036 1103
2700 749 837 915 985 1048
2800 715 798 872 937 996
2900 684 762 831 893 948
3000 654 729 793 851 903
3100 627 697 758 812 861
3200 601 667 725 776 821
3300 577 640 694 742 784
3400 554 613 665 710 750
3500 532 589 637 680 717
3750 483 533 575 611 642
4000 441 484 520 551 577
MLSS SURFACE
LOADING RATES
(mg/l) (gpd/sq.ft.)
2000 2000
2150 2000
2200 1952
2300 1858
2400 1767
2500 1680
2600 1596
2700 1514
2800 1437
2900 1362
3000 1290
3100 1220
3200 1154
3300 1090
3400 1029
3500 971
3750 836
4000 715
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4250 403 441 472 498 520
4500 369 402 429 451 469
4750 340 368 391 409 423
5000 313 337 356 371 382
4250 611
4500 528
4750 459
5000 403
Table 4 - Values For Use in Determining Sludge Storage Requirements
UNDERFLOW
(gpd/sq.ft.)
200 250 300 350 400
RSSS MAX (mg/l) 12813 11743 10935 10295 9771
B L A N K E T
CONC. (mg/l)
7816 7163 6670 6280 5961
POUNDS/CUFT
(Blanket)
0.488 0.447 0.416 0.392 0.372
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SUBCHAPTER G : FIXED FILM AND FILTRATION
§§217.180-217.192
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code as well as the authority to set standards to prevent the
discharge of waste that is injurious to the public health under §26.041 of the Texas Water Code.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.180. Applicability.
This subchapter details the requirements for trickling filters, rotating biological contactors,
submerged biological contactors, and filtration systems.
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§217.181. Trickling Filters - General Requirements.
Trickling filters are secondary aerobic biological processes which are used for treatment of
sewage. Biofilters or biotowers are terms describing trickling filters which use random or stackable
modular synthetic media.
(1) Process Applicability. Trickling filters are classified according to applied hydraulic
loading in million gallons per day (including recirculation) per acre of filter media aerial cross section
surface area (mgd/acre), and influent organic loadings in pounds BOD per day per 1000 cubic feet of
filter media, (lb BOD/day - 1000 cu ft). The following factors shall be considered in the selection of the
design hydraulic and organic loadings: strength of the influent sewage; effectiveness of pretreatment;
type of filter media; and treatment efficiency required. Current practice normally distinguishes among
trickling filter types on the basis of the role in treatment rather than loading rates. Under this system,
trickling filters may be classified as roughing filters providing 50-75% removal of soluble BOD; secondary
treatment filters providing the required settled effluent BOD and TSS; combined BOD/nitrifying filters
providing the required settled effluent BOD, NH4-N, and TSS; and tertiary nitrifying filters which provide
the required settled effluent NH4-N (where the influent to the trickling filter is a clarified secondary
effluent). The applied hydraulic and organic loadings, which the different classes of trickling filters shall
be designed, are presented in Table G.1 of this paragraph. Figure 1: §217.181(1)
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Table G.1 - Typical Design Loadings
Operating Characteristics Standard
Rate
Intermediate
Rate
High
Rate
High Rate Roughing
Media Rock Rock Rock Manufactur
ed
Either
Hydraulic Loading:
mgd/acre
1-4 4-10 10-40 15-90 60-180
Hydraulic Loading: gpd/sf 25-90 90-230 230-900 350-1000 1400-4200
*Organic Loading:
lb BOD5/acre-ft/day
200-1000 700-1400 1000
1300
-- --
*Organic Loading:
lb BOD5/day/1000cf
5-25 15-30 30-150 up to 300 100+
†BOD5 Removal (%) 80-85 50-70 40-80 65-85 40-85
*Does not include recirculation
† Includes subsequent settling
(2) Pretreatment. Rock media trickling filters shall be preceded by primary clarifiers
equipped with scum and grease removal devices. Preliminary treatment shall exist upstream of all
trickling filters. These preliminary treatment units shall effectively remove all grit, debris, suspended
solids, oil, grease, and all particles with a diameter greater than 3 millimeters. Measures to prevent or
control the release of hydrogen sulfide gas shall be provided where influent wastewater potentially
contains harmful or nuisance levels of hydrogen sulfide.
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(3) Rock Filter Media.
(A) Materials. Crushed rock, slag, or similar material shall not contain more
than five percent by weight of pieces whose longest dimension is greater than three times the least
dimension. Rock media shall conform to the following size distribution and grading when mechanically
graded over a vibrating screen with square openings in accordance with the following:
(i) passing five inch sieve - 100 % by weight;
(ii) retained on three inch sieve - 95-100 % by weight;
(iii) passing two inch sieve - 0.2 % by weight;
(iv) passing one inch sieve - 0.1 % by weight; and
(v) the loss of weight by a 20-cycle sodium test, as described in
American Society of Civil Engineers Manual of Engineering and Engineering Practice No. 13, shall be
less than 10%.
(B) Placement. Rock media shall not be less than four feet in depth at the
shallowest point. The dumping of media directly on the filter is unacceptable. Instructions for placing
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media shall be included in the specifications. Crushed rock, slag, and similar media shall be washed and
screened or forked prior to placement to remove clays, organic material, and fines. Rock media shall be
placed by hand to a depth of 12 inches above the underdrains. The remainder of the material may be
placed by means of belt conveyors or equal mechanical methods approved by the engineer. All material
shall be carefully placed in a manner which will not damage the underdrains. Trucks, tractors, or other
heavy equipment shall not be driven over the filter media during or after construction.
(4) Synthetic (Manufactured or Prefabricated) Media Materials. All synthetic media
materials shall be utilized in accordance with all manufacturer’s recommendations. Synthetic media
materials may be considered innovative or nonconforming technology at the discretion of the executive
director and reviewed under §217.10(2) of this title (relating to Types of Approvals) accordingly. If this
type of review occurs, the engineer shall be notified as required by §217.9(d) of this title (relating to
Submittal Requirements).
(A) Suitability. The suitability of synthetic media materials shall be evaluated on
the basis of experience with installations treating similar strength wastewater under similar hydraulic and
organic loading conditions. Case histories involving the use of the media shall be included in the final
engineering design report.
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(B) Durability. Media shall be insoluble in sewage and resistant to flaking or
spalling, ultraviolet degradation, disintegration, erosion, aging, all common acids and alkalies, organic
compounds, and biological attack.
(C) Structural Integrity. The media structural design shall be capable of
supporting the media, water flowing through or trapped in voids, and the maximum anticipated thickness
of wetted biofilm. The media shall additionally be capable of supporting the weight of a person when the
trickling filter is in operation, or separate provisions shall be made for maintenance access to the entire top
of the trickling filter media and to the distributor.
(D) Placing of Synthetic Media. Modular media shall be placed as nearly as
possible with the edges matched, to provide consistent hydraulic conditions within the trickling filter, and
shall be installed to provide a close fit to adjacent modules.
(5) Filter Dosing. Wastewater may be applied to the filters by siphons, pumps, or by
gravity discharge from preceding treatment units when suitable flow characteristics have been developed.
Design for new facilities shall include provisions to control instantaneous dosing rates under both normal
operating conditions and filter-flushing conditions. Unless otherwise justified in the final engineering design
report, optimization of dosing intensity shall be achieved through control of the distributor speed, with
control of recirculation rate as a compensatory measure under low-flow conditions. Table G.2 provides
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design ranges of dosing intensity for normal usage periods and for flushing periods. The instantaneous
dosing intensity for rotary distributors may be calculated using Equation 1.g. Figure 2: §217.181(5)
SK’ [(q% r)( (1000mm/m)]/[(a)(n)(60min/hr)] Equation 1.g
Where:
SK = dosing intensity, mm/pass of an arm;
q = influent flow/filter top surface area, m3/m2/hr;
r = recycle flow/filter top surface area, m3/m2/hr;
a = number of arms; and,
n = revolutions per minute
Table G.2 - Trickling Filter Dosing Intensity Ranges (SK)
BOD5 loading kg/m3/day Design SK mm/pass Flushing SK mm/pass
0.25 10-100 $200
0.50 15-150 $200
1.00 30-200 $300
2.00 40-250 $400
3.00 60-300 $600
4.00 80-400 $800
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(6) Distribution Equipment. Settled wastewater may be distributed over the filter media
by rotary, horizontal, or traveling distributors provided the equipment proposed is capable of producing the
required uniformity of distribution at the design and flushing dosing intensities over the entire surface of
the filter. Deviation from a calculated uniformly distributed volume per unit surface area at the design
dosing intensity shall not exceed 10% at any portion of the filter. Filter distributors shall be designed to
operate properly at all anticipated flow rates. Electrically driven variable speed distributors shall be
provided for new facilities or upgrades of existing trickling filters to allow operation at optimum dosing
intensity independent of recirculation pumping. Excessive head in the center column of rotary distributors
shall be avoided, and all center columns shall have adequately sized overflow ports to prevent water from
reaching the bearings in the center column. Distributors shall include cleanout gates on the ends of the
arms and shall also include an end nozzle to spray water on the wall of the filter to wet the edge of the
media. The filter walls shall extend at least 12 inches above the top of the ends of the distributor arms.
(A) Seals. THE USE OF MERCURY SEALS IS PROHIBITED IN THE DISTRIBUTORS
OF TRICKLING FILTERS. If an existing treatment facility is to be modified, any mercury seals in the
trickling filters shall be replaced with oil or mechanical seals.
(B) Distributor Clearance. A minimum clearance of six inches shall be provided
between the top of the filter media and the distributing nozzles.
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(C) Rate of Travel. Rotary distributor designs shall be capable of operation at
speeds as low as one revolution per 30 minutes, or slower.
(D) Maintenance. Trickling filters designed with a height or diameter which
does not allow distributors to be readily removed and replaced by a crane shall be provided with jacking
columns and pads at the distributor column, or other means to facilitate bearing replacement.
(7) Recirculation.
(A) Low Flow Conditions. In order to ensure that the biological growth on the
filter media remains active at all times, provisions shall be included in all designs for minimum recirculation
during periods of low flow. This minimum recirculation shall not be considered in the evaluation of the
efficiency of the filter unless it is part of the proposed specified continuous recirculation rate. The
required recirculation flow for minimum wetting is minimized in deep filters; however, the required
pumping head shall also be considered in recirculation design. Minimum flow to the filters shall not be
less than 1.0 mgd per acre of filter aerial surface. Minimum flow to the filters shall be sufficient to keep
the distribution nozzles operating properly. In addition, the minimum flow rate for designs using
hydraulically driven distributors shall be great enough to keep rotary distributors turning at the minimum
design rotational velocity. For facilities with a design capacity greater than or equal to 0.5 mgd and in
which recirculation is included in design computations for BOD5 removal, recirculation shall be provided
by variable speed pumps, and a method of conveniently measuring the recycle flow rate shall be provided.
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(B) Compensatory Recirculation. Designs shall provide recirculation to
supplement influent flow where design and flushing dosing intensities are not to be achieved by control of
distributor operation alone. Controls for the distributor speed and recycle pumping rate shall provide
optimum dosing intensity under all anticipated influent flow conditions.
(C) Process Calculations. The benefits of recirculation are considered to be
primarily related to dosing intensity, and may often be achieved by control of the distributor speed only.
Designs which propose recirculation for removal of remaining organic matter in the effluent shall be
justified in the final engineering design report, consider the effect of dilution of the influent on the rate of
diffusion of dissolved organic substrates into the biofilm, and the effect of reduced influent concentrations
on reaction rates in sections of the filter having first order kinetics.
(D) Maximum Recirculation Rate. Recirculation rates in excess of four times
design flow shall not be utilized unless specifically justified in the final engineering design report.
(E) Configuration. Where influent organic loadings are relatively constant, direct
recirculation of unsettled trickling filter effluent may be utilized provided the design ensures that the ability
of the media and distributor nozzles to handle recirculated sloughed biofilm is not exceeded. Where
influent organic loadings are variable, partial concentration equalization may be achieved by recirculating
trickling filter effluent following final clarification. Additional concentration equalization may be achieved
if the recirculated effluent is introduced into the primary clarifiers. If these types of design are proposed,
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clarifiers shall be sized to handle the total influent and recirculated flow, and the clarifier design shall
consider the potential for sludge denitrification and the potential for sludge denitrification shall be reviewed
by the engineer when designing the clarifier.
(8) Average Hydraulic Surface Loading. The engineering report shall include
calculations of the maximum, design, and minimum aerial cross section surface loadings on the filter(s) in
terms of million gallons per acre of filter area per day (for the initial year and design year). Average
hydraulic surface loadings of filters with crushed rock, slag, or similar media shall not exceed 40 mgd per
acre based on design flow except in roughing applications. The minimum surface loading shall not be less
than 1.0 mgd per acre. Loadings on synthetic (manufactured or prefabricated) filter media shall be within
the ranges specified by the manufacturer.
(9) Underdrain System Design. Underdrains with semicircular inverts or the equivalent
shall be provided for rock or other random media. The under drainage system shall cover the entire floor
of the trickling filter. Underdrains for rock media trickling filters shall be vitrified clay or precast
reinforced concrete. Half tile shall not be used for underdrain systems. Inlet openings into the underdrain
shall provide an unsubmerged gross combined area of at least 15% of the surface area of the filter.
Synthetic media of modular stackable designs shall be supported above the filter floor by beams with or
without posts and grating with support and clearances in accordance with the media manufacturer*s
recommendations.
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(10) Underdrain Slopes. Underdrains and the filter effluent channel floor shall have a
minimum slope of one percent. Effluent channels shall be designed to produce a minimum velocity of two
feet per second at design flow rate of application to the trickling filter. Floors of new trickling filters using
stackable modular synthetic media shall slope downward toward the drainage channel at one to five
percent based upon filter size and hydraulic loading.
(11) Passive Ventilation. The underdrain system or synthetic media support structure,
effluent channels, and effluent pipe shall be designed to permit free passage of air. Drains, channels, and
effluent pipes shall have a cross sectional area such that not more than 50% of the cross sectional area
will be submerged at peak flow plus recirculation. Provisions shall be made in the design of the effluent
channels to accommodate the specified flushing hydraulic dosing intensity and to allow the possibility of
increased hydraulic loading. Extensions of underdrains through the filter side walls, ventilating openings
through the side walls, and effluent discharge conduits designed as partially full flow pipes or open
channels may be utilized to assist in ventilation. Vent openings through the trickling filter walls shall be
designed to be capable of hydraulic closure to allow flooding of the filter for nuisance organism control.
Designs using passive ventilation shall provide at least 2.5 square feet of ventilating area (vent stacks,
ventilating holes, ventilating ports, etc.) per 1000 lbs. of primary effluent BOD5 per day. The underdrain
system for rock media filters shall provide at least one square foot of ventilating area for every 250
square feet of plan area. Minimum required ventilating area for synthetic media underdrains shall not be
less than recommended by the manufacturer. The ventilating area shall be the greater of one square foot
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for every 175 square feet of synthetic media trickling filter plan area or 2.6 square feet for every 1000
cubic feet of media volume.
(12) Forced Ventilation. Forced ventilation shall be provided for trickling filters designed
for nitrification, for all trickling filter designs with media depths in excess of six feet, or for locations
where seasonal or diurnal temperatures do not provide sufficient difference between the ambient air and
wastewater temperatures to sustain passive ventilation. The engineer shall determine the minimum air
flows needed for forced ventilation and optimized process performance, and shall provide all calculations
associated with this determination in the final engineering design report. The engineer may use equation
2.g and the values in table G.3 to determine minimum air flow rates. Downflow forced ventilation systems
shall include provisions for removal of entrained droplets, or for return of air containing entrained moisture
to the top of the trickling filter. Downflow systems shall include reversible fans or other provisions to
allow reversal of air flow when wide temperature differences between the ambient air and wastewater
create strong natural updrafts. Ventilation fans and controls shall be designed to enable flooding of the
filter without sustaining damage. Figure 3: §217.181(12)
MAFR’ [(RA)( (L)(PF)]/(1440min/day) Equation 2.g
Where:
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MAFR = Minimum air flow rate, SCFM
RA = Aeration rate, scf/lb Table G.3
L = Loading rate, lb/day, Table G.3
PF = Loading peaking factor
Table G.3 - Aeration Rate and Loading Rate Factors
Filter Application RA (scf/lb BOD5) L (lb BOD5/1000cf/day)
Roughing Filter at 75-200 lb
BOD5/1000cf/day
1080 BOD5 loading on the filter
Secondary Treatment Filter at
25-50 lb BOD5/1000cf/day
1200 BOD5 loading on the filter
Combined or Tertiary Filter 2400 1.25*BOD5 loading on the filter
+ 4.6*TKN loading on the filter
(13) Maintenance.
(A) Cleaning and Sloughing. All flow distribution devices, underdrains, channels,
and pipes shall be designed so the devices may be maintained, flushed, and properly drained. The devices
shall be capable of hydraulically accommodating the specified flush-dosing intensity. The units shall be
designed to facilitate cleaning of the distributor arms. A gate shall be provided in the wall to facilitate
rodding of the distributor arms. Designs shall prevent recirculation of sloughed biomass in pieces larger
than will pass through the distributor nozzles or the filter media voids.
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(B) Nuisance Organism Control. Current practice indicates that nuisance
organisms may be minimized by operation of trickling filters at proper design dosing intensities, with
periodic flushing at higher dosing intensities.
(i) Filter Flies. The structural and hydraulic design of new trickling
filters shall enable flooding of the trickling filters for filter fly control; however, consideration will be given
by the executive director to alternate methods of filter fly control for filters exceeding six feet in height
provided that the effectiveness of the alternate method is verified at a full-scale installation. This
information shall be justified in the final engineering design report. Designs shall minimize adjacent wet
and unwetted areas where filter flies may lay eggs. If existing rectangular trickling filters are retrofitted
with rotary distributors, any media which will not be fully wetted shall be removed.
(ii) Snails. Because snails lay eggs in sludge deposits, trickling filter
designs shall minimize areas where sludge may accumulate. A low velocity, open channel shall be
provided between the trickling filter and final clarifier, for manual removal of snails.
(iii) Corrosion Protection. All equipment and materials utilized in
construction of trickling filters, including ventilation equipment and covers, shall be designed to minimize
corrosion and shall utilize corrosion-resistant materials.
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(14) Flow Measurements. Means shall be provided to measure flows to the filter and
recirculation flows.
(15) Odor Control. Odors shall be minimized by adequate ventilation and by operation of
trickling filters at sufficient design dosing intensities, with periodic flushing at higher dosing intensities.
(A) Covers. The engineer shall consider designing new trickling filters to
accommodate future installation of covers for control of odors and VOC emissions. Covers shall be
provided for new facilities sited in locations where a high potential exists for odor complaints, or for
upgrades of existing facilities having a history of odor complaints. Covers shall allow access to the entire
top of the filter media and to the distributor for maintenance, including removal. Covered trickling filters
shall be equipped with forced ventilation.
(B) Stripping. The engineer shall provide forced ventilation in a downflow mode
to minimize odors for trickling filters with high influent organic loadings. Odorous off-gases may be
recycled through the trickling filter; used to ventilate tertiary nitrifying trickling filters in an upflow mode;
diffused into aeration basins; or treated separately for odor control using scrubbers or adsorption columns.
(16) Final Clarifiers. Final clarifiers for trickling filters shall be sized to provide the
required effluent TSS removal at the maximum influent flow plus maximum recirculation, with all pumps
in operation.
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(17) Treatment Process Design Requirements. The engineer shall provide design
calculations using at least one filter efficiency formula from a reliable source acceptable to the executive
director. Sufficient operating data shall be submitted from existing trickling filters of similar construction
and operation to justify projected treatment efficiency, kinetic coefficients, and other design parameters.
Use of more than one set of applicable design equations is recommended to allow cross-checking of
predicted treatment efficiency.
§217.182. Nitrifying Trickling Filters - Additional Requirements.
This section details requirements which shall be complied with when trickling filters are proposed
as a means of providing nitrification sufficient to meet the requirements of a discharge permit. The
requirements in this section are in addition to the requirements in §217.181 of this title (relating to
Trickling Filters - General Requirements).
(1) Ventilation. Forced ventilation shall be provided for nitrifying trickling filters. Air
flow shall be distributed throughout the underdrain area. Minimum design air flow rates shall provide the
greater of 50 lbs. O2 provided per lb. O2 required at average loading, or 30 lbs. O2 provided per lb. O2
required at peak loading based on stoichiometry.
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(2) Temperature. The temperature utilized in the design equations shall be justified in the
final design engineering report. Temperature effects on removal efficiency may be minimized using deep
towers or other means to minimize recirculation while providing the design hydraulic dosing intensity.
(3) pH. Effects of pH on nitrification in trickling filters may be significant, with optimum
nitrification rates attained above pH 8.0. The final design engineering report shall verify that the design
recirculation rates are appropriate for dealing with the effects of effluent alkalinity and pH depression on
nitrification.
(4) Predation. The biomass of nitrifying filters is subject to predation by flies, snails, and
worms. Means for effective control of biomass predators shall be included in all designs for nitrification.
(5) Hydraulic Application Rates. Designs for nitrifying trickling filters shall
accommodate operation at a design dosing intensity of at least 1.47 gpm/ft2 . The design shall provide
operational control of dosing intensity over a range which accommodates the design conditions.
(6) Media. Crossflow synthetic media is suggested for new tertiary nitrification filters or
for the nitrifying section of new combined nitrification filters.
(7) Tertiary Nitrification Filters. Trickling filters treating influent having a BOD5 to TKN
ratio of # 1.0 and soluble BOD5 # 12 mg/L, are considered tertiary nitrification filters.
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(A) Design Justification. Process design calculations and selection of kinetic
coefficients for tertiary nitrifying filters shall be consistent with current design practices, and shall be
justified by operating data from existing trickling filters of similar construction and operation.
(B) Tower Depth. Tertiary nitrifying filter designs shall minimize pH depression
due to recirculation, by utilizing towers $ 20 feet deep, and by control of influent instantaneous application
rates, by means other than compensatory recirculation. Shallow towers operating in series may be used in
lieu of deep towers, where the design includes provisions to readily switch the operating sequence of the
filters.
(8) Combined BOD/Nitrification Filters. Trickling filters intended to perform nitrification
and treating influent, having a BOD5 to TKN ratio of $ 1.0, or soluble BOD5 $ 12 mg/L, are considered
combined BOD/nitrification filters.
(A) Design Justification. Designs for combined BOD5/nitrification filter designs
shall be empirically based. The projected treatment efficiency and other design parameters shall be
justified by operating data from existing trickling filters of similar construction and operation, and data shall
take precedence over design equations for combined nitrification filter design.
(B) BOD Removal Requirements. Nitrification in combined nitrifying filters
occurs in the lower depths of the filter, or in the second stage of filters operated in series, following BOD
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removal. Designs shall not take credit for nitrification in sections of the filter having soluble BOD5 $ 20
mg/L. Combined nitrification filters shall be designed to achieve effluent total BOD5 # 15 mg/L.
(C) Recirculation. Unlike tertiary nitrification filters, use of recirculation to
achieve design dosing rates may enhance nitrification in combined filters by reducing the influent BOD5 to
TKN ratio. Combined nitrification filter designs shall enable high recirculation rates, with turndown
capability.
§217.183. Dual Treatment Systems Utilizing Trickling Filters .
(a) Classification. Trickling filters or other attached growth treatment units in series with
suspended growth processes are considered to be dual treatment processes.
(1) Activated Biological Filter (ABF). The ABF process consists of a tricking filter and
final clarifier, in which settled solids from the final clarifier are recirculated through the trickling filter, with
no separate aeration basin or solids contact basin.
(2) Trickling Filter/Solids Contact (TF/SC). The TF/SC process consists of a trickling
filter sized to perform the majority of the soluble BOD removal for the system, followed by an aerated
solids contact basin sized to provide polishing and improved sludge settleability, followed by a final
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clarifier. Activated sludge is recirculated to the solids contact basin rather than the trickling filter. A
sludge re-aeration basin may be included in the design.
(3) Roughing Filter/Activated Sludge (RF/AS). The RF/AS process consists of a
trickling filter sized to perform roughing and concentration dampening, followed by an aeration basin sized
to provide the majority of the soluble BOD removal for the system, followed by a final clarifier.
Activated sludge is recirculated to the aeration basin rather than to the trickling filter.
(4) Activated Biological Filter/Activated Sludge (ABF/AS). The ABF/AS process
consists of a trickling filter sized to perform roughing and concentration dampening, followed by an
aeration basin sized to provide the majority of the soluble BOD removal for the system, followed by a final
clarifier. Activated sludge is recirculated to the trickling filter rather than to the aeration basin.
(5) Trickling Filter/Activated Sludge (TF/AS). The TF/AS process consists of a trickling
filter sized to perform roughing and concentration dampening, followed by an intermediate clarifier,
followed by an aeration basin sized to provide the majority of the soluble BOD removal for the system,
followed by a final clarifier. Activated sludge is recirculated to the aeration basin rather than to the
trickling filter.
(b) Process Design. Attached and suspended growth subprocesses in dual systems shall be
designed in an integrated design process which considers the effluent quality from the first stage in
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determining the design basis of the second stage process. Performance of the first stage of treatment
may be estimated using applicable design equations and methodology used for design of single stage
processes. Performance of the second stage of dual systems may not be precisely predicted, and shall be
estimated using data from existing similar installations or applicable pilot studies. Treatment process
designs in which activated sludge is recycled to first-stage trickling filters shall not claim reduction of
oxygen demand to the second-stage aeration basin as a result of sludge recirculation to the trickling filters.
(c) Treatment Unit Design. Detailed design of suspended and attached growth systems shall
include all of the features and operational capabilities required for the same treatment units if used for
single-process treatment, as well as the following items.
(1) Pretreatment. Pretreatment for dual systems shall conform to requirements for the
first-stage process.
(2) Snail Control. A low-velocity channel shall be provided between the first stage and
second stage treatment units for control of snails.
(3) Return sludge. Designs including recirculation of activated sludge or sloughing to
trickling filters shall prevent recirculation of pieces larger than will pass through the distributor nozzles or
the filter media voids. High-rate, vertical flow, fully corrugated media shall be used for trickling filters in
systems where sludge is recirculated to the trickling filter. Sludge shall be pre-incorporated into influent
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prior to application to trickling filters, and shall be pre-incorporated into the effluent from first-stage
processes prior to being introduced into second-stage aeration basins.
(4) Aeration. Aeration system design for second-stage treatment units in systems not
designed for nitrification shall be capable of transferring at least 1.2 lbs. of O2 per lb. of first stage
effluent BOD5 per day. Aeration systems for second-stage treatment units in systems designed for
nitrification shall be capable of transferring sufficient oxygen to meet stoichiometric requirements for
biomass growth, respiration for both carbonaceous material oxidation and nitrification, and oxygen
demand due to biomass sloughing events from the first stage.
(5) Sludge Age. Design of second-stage suspended growth processes shall provide
operational flexibility to vary the sludge age. Mean cell residence time of up to at least 1.5 days shall be
provided in the suspended growth process for TF/SC systems, or of up to at least 3 days if the second
process is an activated sludge aeration basin. Nitrifying dual systems shall be capable of providing control
of total combined mean cell residence time in the attached and suspended growth systems of up to at least
10 days with capability to provide at least 6 days mean cell residence time in the suspended growth
process alone.
(6) Hydraulic Residence Time. Design of second-stage processes shall provide
minimum hydraulic residence time of 0.5 hours if the second process is an aerated solids contact basin,
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and a minimum hydraulic residence time of 3 hours if the second process is an activated sludge aeration
basin.
(7) Nitrification Design. Design for nitrification using dual treatment processes shall
include a sludge reaeration basin if the second process is an aerated solids contact basin, and shall include
an intermediate clarifier if the second process is an activated sludge aeration basin.
§217.184. Rotating Biological Contactors (RBC) - General Requirements.
(a) Pretreatment. RBC units shall be preceded by pretreatment to remove any grit, debris, and
excess oil and grease which may hinder the treatment process or damage the RBC units. Primary
clarifiers, fine screens, and grit removal chambers shall be included if the engineer deems that these types
of units are necessary because the influent waste stream includes or is expected to include high levels of
grease, oil, grit, or other debris. For wastes with high hydrogen sulfide concentrations, preaeration shall
be provided.
(b) Enclosures and Ventilation. RBC units shall be covered, and ample ventilation shall be
provided. Working clearance of approximately 30 inches shall be provided within the cover unless the
covers can be removed with equipment normally available on site. Enclosures shall be constructed of a
suitable corrosion resistant material. Access doors on each end, and observation ports with covers, shall
be provided at 3 foot intervals along the unit.
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(c) Media Design. The design of the RBC media shall provide for self cleaning action due to the
flow of water and air through the media. Only low density media shall be used in the first stage. RBC
media shall be selected which is compatible with the wastewater.
(d) Design Flexibility. The designer of a RBC plant shall consider provisions to provide additional
operational flexibility such as controlled flow to multiple first stages, alternate flow and staging
arrangements, removable baffles between stages, and provision for step feed and supplemental aeration.
(e) Tank Configuration. The RBC tank shall be designed to minimize zones in which solids will
settle out. Tank drains shall be provided to facilitate removal of any accumulated solids.
(f) Control of Unwanted Growth in the Initial Stages. The engineer shall consider provisions for
the addition of chlorine just ahead of the RBC system. In proper dosages, chlorine may control the
growth of beggiatoa which is an unwanted microorganism that may inhibit the initial stage of an RBC
system.
(g) Downtime Maintenance Provisions. Two or more trains (RBC stages in series) shall be
provided for facilities which have a design flow limit of 1 mgd or greater. The trains shall be capable of
being taken off-line when maintenance or cleaning is required. Appropriately-spaced tank drains shall be
included in the design.
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(h) Bearing Maintenance. Bearings shall be easily accessible for inspection and lubrication.
(i) Organic Loading Design Requirements. The organic loading for the design of RBC systems
shall be based on total BOD5 in the waste going to the RBC system including any side streams. The
maximum loading rate shall not exceed 8 pounds of BOD5 per day per 1,000 square feet of media in any
stage. The engineer shall adjust the required RBC media area as needed to compensate for the effects of
the ratio of soluble BOD5 to total BOD5. Allowable organic loading for the entire RBC system shall not
exceed 3.0 square feet (sf) of media area for facilities required to meet secondary treatment with no
nitrification requirements and 2.0 pounds of BOD5/day/1000 sf for facilities required to meet secondary
treatment and nitrification requirements.
(j) Hydraulic Loading Design Requirements. Flow equalization shall be included in the treatment
train when the peak-to-design flow ratio is higher than 2.5 to prevent loss of fixed growth from the media.
A means of spreading the influent flow evenly across the media shall be provided in the first stage of the
RBC system.
(k) Stages. A stage includes one or more RBC units divided by a vertical baffle or wall. The
minimum number of stages in series, for designed only BOD5 removal, shall be three. If the plant is
designed with less than three stages, the engineer shall provide justification in the final engineering design
report. The justification shall be based on either full-scale operating facilities or pilot unit operational data.
Any pilot unit data used in the justification shall take into consideration an appropriate scale-up factor.
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(l) Drive Systems. The drive system for each RBC unit shall be selected for the maximum
anticipated media load. The engineer shall consider installing a variable speed system to provide
additional operator flexibility. The RBC units may be mechanically driven or air driven.
(1) Mechanical Drive. Each RBC unit shall have a positively-connected mechanical
drive with motor and speed reduction unit to maintain the required rpm. A fully-assembled spare
mechanical drive unit for each size shall be provided on-site. Supplemental diffused air shall be
considered for mechanical drive systems to help remove excess biomass from the media and to help
maintain the minimum dissolved oxygen concentration.
(2) Air Drive. Each RBC unit shall have air diffusers mounted below the media and off-
center from the vertical axis of the RBC unit. Air cups mounted on the outside of the media shall collect
the air to provide the driving force and maintain the required rotational speed. Blowers shall provide
enough air flow for each RBC unit plus additional capacity to double the air flow rate to any one unit
while the others are running normally. The blowers shall be capable of providing the required air flow
with the largest unit out of service. The air diffuser line to each unit shall be mounted such that the air
diffuser line may be removed without removing the RBC media. An air control valve shall be installed on
the air diffuser line to each RBC unit.
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(m) Dissolved Oxygen. The RBC plant shall be designed to maintain a minimum dissolved
oxygen concentration of one milligram per liter in all stages during the maximum organic loading rate.
Supplemental aeration may be required.
§217.185. Nitrifying RBCs - Additional Requirements.
For BOD5 removal and nitrification of domestic wastewater in a single system, a minimum of four
stages shall be used, and the maximum overall organic loading rate shall be 1.6 pounds of BOD5/day/1,000
square feet of media. When the influent pH is consistently below 7.0, capabilities for chemical addition,
as needed to increase the pH, shall be provided. RBC designs which are intended to provide nitrification
shall be substantiated by data and calculations in the final engineering design report to the satisfaction of
the executive director. These requirements are in addition to the requirements of §217.184 of this title
(relating to Rotating Biological Contactors (RBCs - General Requirements). These designs may be
subject to the requirements of §217.10(2) of this title (relating to Types of Approvals) at the discretion of
the executive director.
§217.186. Dual Treatment Systems Utilizing RBCs.
RBC units may be used in conjunction with other systems to take advantage of the strengths of
both systems. An RBC system may be used as a "roughing" unit in series with activated sludge as
described in §217.183 of this title (relating to Dual Treatment Systems Utilizing Trickling Filters).
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Regardless of the type of dual system employing RBC units, the engineer shall submit supporting data,
calculations, process descriptions, and vendor information to describe how the proposed system will meet
the required treatment levels. These systems may be subject to the requirements of §217.10(2) of this
title (relating to Types of Approvals) at the discretion of the executive director.
§217.187. Submerged Biological Contactors (SBC) - General Requirements.
SBC units are generally larger in diameter than RBC units. The majority of the SBC unit is
submerged in the mixed liquor, including the media support shaft and bearings. As a result, SBC systems
are only air driven and do not require covers. SBC systems require the same pretreatment as RBC
systems. SBC systems shall be designed under the same criteria as RBC systems except as described in
paragraphs (1) and (2) of this section. The engineer shall submit design supporting data, calculations,
process descriptions, and vendor information in the final engineering design report to describe how the
proposed system will provide the required treatment levels. These designs may be subject to the
requirements of §217.10(2) of this title (relating to Types of Approvals) at the discretion of the executive
director.
(1) Number of Headers. Two air headers are required for each SBC unit: one for
rotation of the unit and one to provide dissolved oxygen for the biological activity.
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(2) Bearing Requirements. The submerged bearings shall be sealed to prevent intrusion
of the wastewater. If lubrication is required, facilities shall be provided above the water level to provide
the lubricant without draining the tank.
§217.188. Dual Treatment Systems Utilizing SBCs.
SBC units may be used in conjunction with other systems to take advantage of the strengths of
both systems. An SBC system may be used as a "roughing" unit in series with activated sludge as
described in §217.183 of this title (relating to Dual Treatment Systems Utilizing Trickling Filters). SBC
units may also be installed in existing activated sludge basins to create a combination fixed and suspended
growth process. Regardless of the proposed dual system employing SBC units, the engineer shall submit
supporting data, calculations, process descriptions, and vendor information in the final engineering design
report to describe how the proposed system will provide the required treatment levels. These designs
may be subject to the requirements of §217.10(2) of this title (relating to Types of Approvals) at the
discretion of the executive director.
§217.189. Filtration - General Requirements.
(a) Reasons for Use.
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(1) Permit Requirements. Filtration shall be used as a unit operation to supplement
suspended solids removal for those treatment facilities with tertiary effluent limitations (e.g., total
suspended solids effluent quality less than 15 milligrams per liter).
(2) Specific Water Quality Requirements. Filtration may be used as a unit operation for
those treatment facilities with secondary or advanced secondary effluent limitations. Filtration normally
provides effective removal for suspended biological floc and residual materials which remain after
secondary clarification. Intermittent filter operation is acceptable where filters are not necessary to meet
permitted effluent limitations. Filtration may also reduce oxygen-demanding substances by removing the
non-soluble fraction of the clarifier effluent.
(b) Redundancy. If filters are being used to provide tertiary treatment for a permit requirement,
a minimum of two filter units shall be provided, and the required filter surface area shall be calculated
assuming the largest filter unit out of service. If filters are being provided voluntarily to polish wastewater
for situations where permit compliance does not in any way depend on the use of the filter, such as some
cases of reclaimed water usage, one filter is sufficient.
(c) Source of Backwash Water. Filtered effluent shall be used as the source of backwash
water.
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(d) Disposition of Backwash Water. Backwash water containing material cleaned from the filter
shall be returned to the head of the treatment plant for processing.
(e) Place in Sequence of Treatment Units. Filter units shall be preceded by final clarifiers
designed in accordance with Subchapter F of this Chapter. Filter systems may be used in conjunction
with disinfection tanks to provide additional detention time, provided the filters are backwashed to the
headworks of the wastewater treatment facility.
(f) Overload Conditions. During times of peak flows or excessive carryover of suspended solids
from the final clarifier (40 to 50 milligrams per liter or more) for an extended period of time, the filter units
may overload. The filter run time may be abbreviated to the point that the filter becomes inoperable.
Provisions shall be made to prevent the effluent from overflowing from the wastewater treatment system
and to prevent damage to the wastewater treatment system equipment during these times.
(g) Control of Slime Growth. Facilities to provide continuous or periodic disinfectant in the
influent stream to the filters shall be provided to control slime growth in the filter and backwash storage
tank.
§217.190. Additional Specific Design Requirements for Deep Bed, Intermittently Backwashed,
Granular Media Filters.
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This subsection contains design criteria for deep bed, intermittently backwashed, granular media
filters. These requirements are in addition to the requirements in §217.189 of this title (relating to
Filtration - General Requirements).
(1) Application Rates. The design flow of the plant shall be used with the design
filtration rates below. The peak application rate to any unit shall not exceed twice the design application
rate with one unit out of service.
(A) Single Media. The design filtration rate for single media (sand) filters shall
not exceed 3 gallons per minute per square foot of media surface. The maximum filtration run time
between backwash periods shall be 6 hours.
(B) Dual Media. The design filtration rate for dual media (anthracite and sand)
filters shall not exceed 4 gallons per minute per square foot of media surface.
(C) Mixed Media. The design filtration rate for mixed media (non-stratified
anthracite, sand, garnet, or other materials) shall not exceed 5 gallons per minute per square foot of media
surface.
(2) Media Design. A graded gravel layer with a minimum depth of 15 inches, or other
filter media support material, shall be provided over the filter underdrain system. Filter media other than
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gravel shall be described and technically justified in the final engineering design report. Media depths for
the various filter types shall conform to the values in table G.4. Media depths significantly different than
these shall be justified in the final engineering design report. The justification shall include an analysis of
the backwash rates. Uniformity coefficients shall be 1.7 or less. The particle size distribution for dual
and mixed media filters shall result in a hydraulic grading of material during backwash which will result in
a filter bed with a pore space graded progressively coarse to fine from the top of the media to the
supporting layer. Figure 1: §217.190(2)
Table G.4 - Minimum Filter Depths for Deep Bed, Intermittently Backwashed Filters
Filter Type Type of Media Effective Particle Size
(mm)
Minimum Depth
(inches)
Single Media Sand 1.0-4.0 24
Dual Media Anthracite & Sand 1.0-4.0 16
Dual Media Anthracite 1.0-2.0 10
Dual Media Sand 0.5-1.0 6
Mixed Media Anthracite, Sand &
Other
1.0-4.0 16
Mixed Media Anthracite 1.0-2.0 10
Mixed Media Sand 0.6-0.8 4
Mixed Media Garnet or Similar
Material
0.3-0.6 2
(3) Backwash Systems
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(A) Flowrate and Media Expansion. The backwash system shall provide for a
minimum media expansion of 20%. For single media filters, a minimum backwash flowrate of 6 to 8
gallons per minute per square foot of media area shall be provided. For dual and mixed media, a minimum
backwash rate of 15 to 20 gallons per minute per square foot of media area shall be provided. Backwash
times of 10 to 15 minutes shall be provided, unless otherwise justified in the final engineering design
report.
(B) Surge Control. To minimize hydraulic surges on the plant, a backwash tank
shall be provided for plants which do not have flow equalization or other means of surge control. The
surge control shall prevent increases in flow greater than 15% of the design flow of the upstream
treatment units. For this purpose, an influent lift station is not considered a treatment unit. The engineer
shall provide calculations demonstrating that the design has appropriately accounted for the effects of
backwash water. The calculations shall show that the plant’s treatment capabilities will not diminish with
the return of backwash water to the plant’s headworks. Enclosed backwash tanks shall be vented to
maintain atmospheric pressure.
(C) Pumps. Pumps for backwashing filter units shall be designed to deliver the
required rate with the largest pump out of service. The backup pump unit may be uninstalled provided
that the spare unit may be quickly installed and placed into operation. Valve arrangement for isolating a
filter unit for backwashing shall be readily accessible for the operator. Provision for manual override shall
be provided for any backwash system employing automatic control.
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(D) Supplemental Systems. An air scour system or combination air and water
scour system shall be provided in addition to the upflow backwash water system for single media filter
systems. For dual and mixed media filter systems, a surface air or water scour system shall be provided.
Air scour flowrates shall be 3 to 5 standard cubic feet per minute per square foot of media surface area,
and water scour flowrates shall be 0.5 to 2 gallons per minute per square foot of media area.
(4) Underdrain System. The filter underdrain system shall allow the passage of the
maximum filtration flowrate and the maximum backwash flowrate without excessive head loss. The
system shall be suitable for wastewater treatment, provide a uniform distribution for filter backwash, and
not be susceptible to excessive plugging.
(5) Tank Design. The bottom of the wash water collection troughs shall be a minimum
of 6 inches above the maximum elevation of the expanded media during backwash. A minimum
freeboard of 3 inches shall be provided in the washwater troughs during maximum backwash flowrates.
(6) Controls. The filter operation may be controlled manually or automatically. Control
indicators shall be mounted such that the operator may see the filter while adjusting the controls. If the
system is automatically controlled, a manual override system shall be provided. Each filter unit shall be
provided with a head loss indicator.
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§217.191. Additional Specific Design Requirements for Multi-Compartmented, Low Head,
Automatically Backwashed Filters.
This subsection contains design criteria for multi-compartmented, low head, automatic backwash
filters. These requirements are in addition to the requirements detailed in §217.189 of this title (relating to
Filtration - General Requirements).
(1) Application Rates. The design flow of the plant shall be used with the design
filtration rates in subparagraphs (A) and (B) of this paragraph. The peak application rate to any unit shall
not exceed twice the design application rate with one unit out of service. Manufacturer's recommended
filtration rates may be considered if substantiated with test data.
(A) Single Media. The design filtration rate for single media (sand) filters shall
not exceed 3 gallons per minute per square foot of media surface.
(B) Dual Media. The design filtration rate for dual media (anthracite and sand)
filters shall not exceed 4 gallons per minute per square foot of media surface.
(2) Media Design. Filter media support material shall be used in each compartment (or
cell) of the filter. The support material shall be design to resist penetration of the filter media into the
support material. Filter media shall allow passage of the maximum filtration flowrate and maximum
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backwash flowrate without excessive head loss. The support material shall be suitable for wastewater
treatment, provide for a uniform distribution of filter backwash, and not be susceptible to excessive
plugging. Media sizes and depths shall correspond to the values in table G.5. Media sizes and/or depths
significantly different from these shall be justified in the final engineering design report. Figure 1:
§217.191(2)
Table G.5 - Filter Depths for Multi-Compartmented, Low Head, Automatic Backwash Filters
Filter Type Type of Media Effective Particle Size
(mm)
Minimum Depth
(inches)
Single Media Sand 0.55-0.65 11
Dual Media Anthracite & Sand 0.55-0.65 16
Dual Media Anthracite 1.0-2.0 10
Dual Media Sand 0.5-1.0 6
(3) Backwash System. The backwash system shall provide a minimum of 20 gallons per
minute per square foot of media being backwashed at a given time (usually one compartment or cell).
The backwash shall have a duration of 20 to 30 seconds for each compartment, and the backwash shall
expand the media a minimum of 20%. Manufacturer's recommended backwash rates may be considered
if substantiated with test data. The surge control and pumping system requirements shall be the same as
those detailed in §217.190(3)(B) of this title (relating to Additional Specific Design Requirements for
Deep Bed, Intermittently Backwashed, Granular Media Filters)
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(4) Traveling Bridge. The traveling bridge mechanism shall provide support and access
to the backwash pumps and equipment. The bridge shall be constructed of corrosion resistant materials,
and shall have provisions for consistent tracking of the bridge and safe support of the power cords. The
bridge shall begin moving and initiate the backwash cycle automatically when a preset head loss through
the filter media occurs.
(5) Surface Floatables Control. A system shall be provided to automatically and
regularly remove any floating material from the surface of the filter. This material shall be returned to the
head of the plant for further processing.
§217.192. Alternative Designs for Effluent Polishing.
Use of other processes for tertiary suspended solids removal, other than filters such as
microscreens or countercurrent, continuous filtrate and backwash flow filters, will be considered
nonconforming technologies and shall be subject to the requirements of §217.10(2) of this title (relating to
Types of Approvals).
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SUBCHAPTER H : NATURAL SYSTEMS
§§217.200-217.210
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code as well as the authority to set standards to prevent the
discharge of waste that is injurious to the public health under §26.041 of the Texas Water Code.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.200. Applicability.
This subchapter provides the minimum design requirements for Imhoff tanks, constructed
wetlands, facultative ponds, aerated and partially-aerated ponds, stabilization ponds, treated effluent
storage ponds, evaporative pond systems, and overland flow processes.
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§217.201. Primary and Secondary Treatment Units.
Aerated and partially-aerated ponds, facultative ponds, and Imhoff tanks are considered primary
treatment units. Stabilization ponds, constructed wetlands, and overland flow processes are considered
secondary treatment units or processes. Evaporative ponds are used as both primary treatment units and
secondary treatment units. The secondary treatment options may also be used for polishing and tertiary
treatment; however, unless otherwise clarified in this subchapter, they shall be assumed to be secondary
treatment units. Treated effluent storage ponds are considered to be any ponds downstream of the permit
sampling location, and are not considered to provide any treatment or disinfection for the purposes of this
Chapter. All secondary treatment units shall be preceded by a primary treatment unit. All units which
are being utilized to comply with tertiary permit requirements shall be preceded by both primary and
secondary treatment units. If natural system treatment units are utilized for tertiary treatment, the degree
of treatment expected and the technical justification to support the expected treatment levels shall be
detailed in the final engineering design report. The executive director shall have the option of requesting
additional information regarding the use of natural treatment systems for tertiary treatment prior to
granting approval of such systems.
§217.202. General Design Considerations for Natural Systems.
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This section outlines a variety of requirements which apply to one or more of the natural systems
detailed in this subchapter. Each of the subsections of this section will include specific references to the
natural treatment systems or units for which the design criteria detailed in the subsection apply.
(1) Flow Distribution. This subsection applies to constructed wetlands, overland flow
processes, facultative ponds, aerated and partially-aerated ponds, stabilization ponds, and overland flow
processes. These treatment facilities shall be of such shape and size to ensure even distribution of the
wastewater flow. The distribution system for overland flow processes shall be designed in a manner
which ensures sheet flow distribution of the wastewater. The sheet flow shall be uniform onto and across
the overland flow terraces.
(2) Windbreaks & Screening. This section applies to all natural system treatment units
listed in §217.200 of this title (relating to Applicability). Windbreaks shall be considered when spray
irrigation is utilized in a location where drift may present a risk of contact with the general public.
Vegetative screening shall be considered when aesthetic factors might improve project acceptance with
the general public. All decisions regarding the use, the type, and the extent of windbreaks or vegetative
screening shall be left to the best professional judgement of the engineer unless required by the executive
director.
(3) Maximum Liner Permeability. This section does not apply to evaporative pond
systems or overland flow systems. Liner and permeability requirements for these systems are detailed in
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§§217.207 and 217.209 of this title (relating to Evaporative Ponds and Overland Flow Process). Except
as exempted in paragraphs (1) and (2) of this section, this section applies to constructed wetlands,
facultative ponds, earthen aerated and partially-aerated ponds, stabilization ponds, and treated effluent
storage ponds. These treatment units shall be constructed with a liner which is as restrictive as, or more
restrictive than, material with a coefficient of permeability of 1x10-7cm/sec with a thickness of 2 feet at
depths less than 8 feet and 3 feet at depths greater than 8 feet. For the purposes of this subchapter, the
liner shall extend from the lowest pond or constructed wetland elevation up to an elevation of 2 feet above
normal water elevation in the pond or constructed wetland.
(A) If a wastewater discharge permit contains language which allows a variance
to the liner requirements, the permit requirement shall supersede the requirements of this subsection.
(B) If a pond is constructed to store treated wastewater which is to be utilized as
reclaimed water in accordance with an authorization under 30 TAC Chapter 210 of this title (relating to
the Uses of Reclaimed Water), the pond liner requirements shall comply with the requirements of
relevant Chapter 210 and supersede the requirements of this subsection.
(4) Method of Ensuring that the Maximum Liner Permeability is not Exceeded.
Subparagraphs (A)-(D) of this paragraph provide the minimum criteria for satisfying the executive
director that the liner’s permeability will not exceed that allowed in paragraph (3) of this section. The
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results of any tests required in this subsection shall be included in the final engineering design report under
the seal of a licensed professional engineer in the State of Texas.
(A) Using Unmodified In-Situ Soils. In some cases ,the soils which naturally
exist at a proposed pond or constructed wetland site may restrict the movement of the wastewater to a
degree equivalent to a liner placed as described in paragraph (2) of this section. If the engineer believes
this situation to be the case, the following protocol shall be followed to verify the permeability of the in-situ
soil layer and ensure that groundwater quality and surface water quality are protected. A minimum of
one core sample per 0.25 acres of pond bottom area, or constructed wetland bottom area, shall be taken
for each pond or constructed wetland. Each core sample shall be tested to determine the coefficient of
permeability, the percent passing a 200 mesh sieve, the liquid limit value, and the plasticity index value for
the 2 feet of soil (or 3 feet of soil for portions of the pond holding more than 8 feet of wastewater at
normal elevation) which is to serve as the liner. The results of the tests shall show a coefficient of
permeability of less than or equal to 1x10-7 cm/sec and compliance with subparagraph (B)(i)-(iii) of this
paragraph. If the test results do not show a coefficient of permeability of 1x10-7 cm/sec or less along with
the appropriate liner thicknesses, or if any of the soil characteristics in subparagraph (B)(i)-(iii) of this
paragraph do not exist in the in-situ soil, the liner shall be constructed in accordance with one of
subparagraphs (2), (3), or (4) of this section. If the in-situ soil meets all these requirements, the in-situ soil
may be used as the pond liner or constructed wetland liner provided that one layer of excavated in-situ
material, which meets all the minimum soil characteristic requirements, is placed in one 8-inch loose lift
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compacted to no less than 6 inches at 95% standard proctor density in accordance with ASTM D 698.
This placed layer shall be keyed into the in-situ soil.
(B) Placed Liners. The soil characteristics of the liner material of a placed liner
shall, at a minimum, comply with clauses (i)-(v) of this subparagraph. The tests to determine the soil
characteristics shall conform to standard method such as ASTM.
(i) The liner material shall have more than 30% passing a 200 mesh
sieve;
(ii) The liner material shall have a liquid limit greater than 30%;
(iii) The liner material shall have a plastic index of greater than 15;
(iv) The liner material shall be placed in four-eight inch maximum loose
lifts which shall be compacted to 95% standard proctor density in accordance with ASTM D 698. The
lifts shall be no less than 6 inches thick after compaction for a total liner width of at least 24-inches (2
feet); and,
(v) The lowest level lift shall be keyed into the existing soil.
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(C) Using Modified In-Situ Soils. Soil admixtures such as bentonite clay may be
blended with imported soils, or soils excavated from the proposed pond site, to obtain a less permeable
material for use as a liner. If soil admixtures are used, the soil shall be amended sufficiently to decrease
the coefficient of permeability to 1x10-8 cm/sec. This permeability shall be verified by taking three
representative samples from each 6,700 cubic feet of amended soil, running one field permeability test and
running one laboratory permeability test for each of the three representative samples. If the tests do not
verify that the coefficient of permeability is equal to or less than 1x10-8 cm/sec, additional soil admixture
shall be blended into the soils and the tests shall be repeated. This process shall continue until all the
amended soils achieve a coefficient of permeability of 1x10-8 cm/sec or less, as verified by the testing
requirement. The liner shall not be placed until the proper coefficient of permeability is obtained for the
amended soil. When soil permeabilities are decreased in this manner, the liner thickness throughout the
pond may be decreased to 6-inches provided that the liner is placed in one 8-inch loose lift compacted to
no less than 6-inches at 95% standard proctor density in accordance with ASTM D 698. This placed layer
shall be keyed into the in-situ soil. Alternatively, the coefficient of permeability may be 1x10-7cm/sec if
the modified material is placed in accordance with subparagraph (B)(iv) and (v) of this paragraph.
(D) Using synthetic membrane liners. Synthetic membrane liners shall have a
minimum thickness of 40 mils. Ponds with membrane liners shall be designed with an underdrain leak
detection system which shall consist of, at a minimum, a leachate collection and a detection system.
Proper compaction of soils beneath the liner shall be required by the construction specifications. The liner
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material shall be capable of receiving constant sunlight without degrading. This option shall not be used
for constructed wetlands liners.
(5) Embankment Design and Construction. This section applies to constructed wetlands,
facultative ponds, aerated and partially-aerated ponds, stabilization ponds, treated effluent storage ponds,
and evaporative ponds. The top width of embankments shall be a minimum of 10 feet to permit access of
vehicles and maintenance equipment. INNER AND OUTER EMBANKMENT SLOPES STEEPER THAN 1 FOOT
VERTICAL TO 3 FEET HORIZONTAL ARE PROHIBITED. The engineer shall justify designing any slope
steeper than 1 foot vertical to 4 feet horizontal from the top down to the normal operating level to allow
for safer mower access. All embankments shall be protected against erosion by such measures as
planting grass, paving, or riprapping. Flatter slopes may have the disadvantage of added shallow areas
conducive to emergent vegetation. Where embankments are to be vegetated, a minimum cover of 6
inches of topsoil shall be provided.
(6) Disinfection. If a detention time of at least 21 days is provided in the entire, free-
water surface, natural system, chemical or ultraviolet disinfection is not required.
(7) Sampling Point Significance. Detention times and surface areas of any natural
treatment units or processes, which are downstream of the sampling point used to monitor for permit
compliance, are not allowed to be counted for purposes of sizing treatment units upstream of the permit
monitoring sampling point. All wastewater ponds downstream of the sampling location shall be considered
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to be treated effluent storage ponds for the purposes of this rule. Treated effluent storage ponds are
utilized to comply with municipal permit storage requirements or for reclaimed water projects authorized
by Chapter 210 of this title (relating to Use of Reclaimed Water). In these cases, if a conflict exists
between the requirements of the permit or reclaimed water authorization and this Chapter, the
requirements of this chapter which are in conflict shall be waived, and the ponds shall be designed and
constructed to meet the permit or Chapter 210 of this title requirements.
(8) Storm Water Drainage. Storm water drainage shall be prevented from entering all
natural treatment systems.
§217.203. Imhoff Tanks.
This section provides the design criteria which shall be utilized when constructing Imhoff tanks.
(1) Settling Compartment. The length-to-width ratio of the settling compartment shall be
2:1 or greater. The tank inlet shall be designed to provide uniform flow distribution across the width of the
settling compartment. The septum walls shall slope to the center of the compartment at an angle of 50 to
60 degrees from horizontal. The septum walls shall be designed to create an overlap, with a continuous
slot at least 8 inches wide provided between the walls, to allow solids to be dispersed into the digestion
compartment. Maximum depth between the normal water level and the plane of the slot shall be 9 feet.
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At least 18 inches of freeboard, above the normal water level, shall be provided. One of the walls shall
continue past the slot to create a slot overhang. The slot overhang shall be a minimum of 8 inches.
(2) Surface Loading. The design loading rate is dependent upon the surface area of the
settling compartment. The settling compartment loading rate shall not exceed 800 gallons per day per
square foot of settling compartment area under design flow conditions. The longitudinal velocity of
wastewater through the settling compartment shall not exceed 1 foot per second under 2-hour peak flow
conditions.
(3) Scum Baffles. Scum baffles shall be provided at the inlet and outlet of the tank.
Baffle height above and below normal water level shall consider the water levels at minimum and at peak
flows.
(4) Gas Vents. Gas vents shall be provided parallel to the settling compartment, and the
total area of vents shall not be less than 20% of the total tank surface area. Width of the vent openings
shall allow maintenance access into the digestion compartment.
(5) Digestion Compartment - Loading. The digestion compartment minimum volume
shall be 3.5 cubic feet per capita or 20.5 cubic feet per pound of influent BOD5 per day, whichever is
greater.
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(6) Imhoff Tank Dimensions. The first 18 inches of tank depth below the plane of the
slot is considered the “neutral zone” and shall not be included as design digestion volume. The total depth
of the Imhoff tank shall not be less than 15 feet as measured from the water surface elevation to the
bottom of the digestion compartment.
(7) Sludge Removal. The Imhoff tank shall have the capability to withdraw sludge from
the digestion compartment through a sludge withdrawal pipe. The sludge withdrawal pipe shall have a
minimum diameter of 8 inches and provide ample cleanouts or other provisions for regular cleaning. The
digestion compartment shall be constructed in a manner which allows portable pumps to remove sludge
which has accumulated in the Imhoff tank.
(8) Odor Management. As deemed necessary by the engineer, the effects of periodic
offensive odors from the gas vents on the neighboring properties shall be minimized or eliminated. In
cases where Imhoff tanks will be constructed and installed next to residences, the executive director may
require odor control devices such as bio-filters and carbon filters to minimize odors.
(9) Treatment Efficiency. Imhoff tanks provide only primary sedimentation of the raw
wastewater and shall be followed by subsequent treatment units. For design of subsequent units, a 35%
removal of influent BOD5 and 60% removal of influent TSS may be assumed for typical municipal raw
wastewater.
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(10) Material and Construction. Imhoff tanks shall be constructed of reinforced
concrete. All concrete used in the Imhoff Tank shall include a factory installed liner which is resistant to
the corrosive effects of the sewage environment. All components of the Imhoff Tank shall be resistant to
the corrosive effects of the sewage environment.
§217.204. Facultative Ponds.
(a) Configuration/Inlets/Outlets. The length-to-width ratio of the facultative pond shall be three
to one (3:1). Other dimensions more suitable to the site may be used upon justification by the design
engineer in the engineering report. For facultative ponds, flow shall be from the inlets along one end of
the pond to the outlets at the opposite end. The length of the facultative pond shall be oriented in the
direction of the prevailing winds with the inlet side located such that debris will be blown toward the inlet.
Inlet baffles shall be provided in facultative ponds to collect floatable material when no prescreening is
provided. The outlets shall be constructed so that the water level of the traditional facultative pond may
be varied under normal operating conditions. The engineer may wish to locate facultative ponds in a
central location with regard to the surrounding secondary ponds to facilitate compliance with the buffer
zone requirements specified in Chapter 309 of this title (relating to Domestic Wastewater Effluent
Limitations and Plant Siting).
(b) Depth. For the facultative pond design, the portion of the pond near the inlets shall have a
depth of not less than 12 feet to provide sludge storage and anaerobic treatment. This deeper portion shall
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be at least 25 percent of the area of the pond bottom. The remainder of the facultative pond shall have a
depth of not less than 8 feet.
(c) Organic loading. The organic loading, based on the surface area of the facultative pond, shall
not exceed 150 pounds of BOD5 per acre per day.
(d) Odor Control. The facultative pond inlets shall be submerged at least 24 inches below the
water surface to minimize odor and the outlets shall be submerged at least 12 inches below water surface,
but shall not disturb the anaerobic zone. Capabilities for recirculation at 50% to 100% of the design flow
shall be provided for facultative ponds. Facultative ponds shall be designed to preclude situations where
siphoning of pond contents through submerged inlets may occur.
(e) Removal efficiency. Up to 50% of the influent BOD5 may be assumed to be removed in the
facultative pond.
§217.205. Aerated Ponds.
Complete mix aerated ponds are those which have adequate mixing to maintain all biological
solids in suspension and provide uniform oxygen concentrations in the pond. Partially mixed aerated
ponds allow for settling and anaerobic composition of a portion of the influent suspended solids as well as
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the biological solids generated in the system. The requirements of this section apply to both completely
mixed ponds and partially mixed ponds, except where otherwise specified.
(1) Wastewater Oxygen Requirements. Mechanical or diffused aeration equipment for
aerated pond systems shall be sized to provide a minimum of 1.6 pounds of oxygen per pound of influent
BOD5.
(2) Redundancy. The oxygen requirements for aerated pond systems shall be
maintained with the largest unit in each pond out of service. If the pond system’s piping and valves are
such that flow may be proportionally rerouted and the aeration equipment is equipped with alarms which
will provide sufficient notification to ensure maintenance can be provided which prevents permit
violations, the system may be sized to provide a minimum of 1.6 pounds of oxygen per pound of influent
BOD5 assuming the largest single aeration unit in the overall pond system out of service.
(3) Removal Efficiency. The basis for calculating the BOD5 removal in each pond shall
be equation 1.h. For domestic wastewater and a complete mix pond, the value of K shall be 0.50 day-1 at
20°C. If the aerated pond is designed for partial mixing, a K value of 0.28 day-1 at 20°C shall be used.
The value, K, shall be adjusted for the minimum monthly water temperature using equation 2.h. Values
for K for high-strength or industrial wastewater shall be determined by either laboratory studies or
evaluation of existing facilities treating a similar wastewater. Figure 1: §217.205(3)
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E’1[1%K(V/Q)] Equation 1.h
where: E = efficiency of a complete mix reactor, in this case an aerated
lagoon, without recycle (% BOD5 removal in aerated lagoon).
K = first order removal rate constant, day-1.
V = aeration basin volume, million gallons.
Q = influent wastewater flow rate, million gallons per day.
KT ’ [K20(1.06( (T&20EC)]/1.06 Equation 2.h
where: KT = K value which corresponds to the lowest average water
temperature expected during any 30-day period.
K20 = K value at 20EC
T = The average water temperature expected during any 30-day
period.
(4) Aeration Equipment. The aeration equipment in aerated ponds shall be sized to
supply the oxygen demand determined in paragraph (1) of this section. For purposes of sizing aeration
equipment, aerated ponds shall be assumed to be the same as an aeration basin and shall comply with the
mechanical and diffused air requirements in §217.156 of this title, (relating to Aeration Equipment Sizing).
Where multiple partially mixed aerated lagoons are utilized in series, the power input may be reduced as
the influent BOD5 to each pond decreases.
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(5) Aerated Pond Construction and Design Requirements. Aerated ponds shall be
designed and constructed in accordance with all the same requirements for wastewater treatment ponds
detailed in §§217.202(e), 217.206(2), (4), and (6) of this title (relating to General Design Consideration for
Natural Systems and Wastewater Stabilization Ponds).
(6) Scour Prevention. All earthen lined aerated lagoons shall include concrete scour
pads in all areas of the earthen liner which will be subject to velocities of 1 foot per second or greater.
§217.206. Wastewater Stabilization Ponds.
This subsection applies to ponds which are designed as secondary treatment units to treat
suspended and dissolved organic matter in wastewater. When utilizing these stabilization ponds, the
settleable and floatable solids in the influent wastewater shall be removed by primary treatment prior to
discharge into the stabilization ponds.
(1) Odor Management. Wastewater stabilization ponds shall be located so that the local
prevailing winds will be toward uninhabited areas. Where clean water is available, the ponds shall be
prefilled to the two foot level to encourage rapid start-up of the biological process and to discourage odor.
The pond system shall include a piping arrangement which allows the recirculation of effluent from the
final pond to the influent side of the initial stabilization pond. Recirculation provides active algal cells to
the upstream feed area, providing photosynthetic oxygen for organic digestion. Recirculation also
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provides a more completely-mixed environment within the pond system. A return of recirculation water
by surface spray, to assist in maintaining aerobic conditions at the pond surface and reduce potential
odors, may be used.
(2) Minimum Number of Wastewater Stabilization Ponds. All pond systems, which
utilize stabilization ponds to comply with secondary or tertiary treatment limits in a municipal wastewater
permit, shall have a minimum of two stabilization ponds. The stabilization ponds shall be operated in series
with each other following the primary treatment unit.
(3) Pond Dimensions and Water Level Considerations. The length-to-width ratio of the
ponds shall be at least 3:1. No islands, peninsulas, or coves shall exist within the ponds boundaries. The
stabilization ponds shall have a normal water depth of 3 to 5 feet. Inlet and outlet structures shall allow
for raising and lowering water levels a minimum of 6 inches to assist in controlling weeds and other
vegetative growth. A 2 foot minimum freeboard shall be provided above the normal pond operating level.
A 3 foot minimum freeboard shall be provided for ponds whose normal water surface area is 20 acres or
less.
(4) Hydraulic and Piping Considerations. The hydraulic capacity of all structures and
piping incorporated in a pond system shall be sized to transport at least 250% of the facility’s design flow.
The inlet and outlet structures shall be sized to hydraulically pass the volume of water found in the top 6
inches of the pond during normal operating depths, per day, at the available head. The pond system’s
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piping and recirculation arrangement shall be designed in a manner which allows any one pond to be taken
out of service while maintaining a level of water quality which complies with the facility’s permit
requirements.
(5) Maximum Organic Loading on Stabilization Ponds. The maximum organic loading
rate on the stabilization ponds shall be 35 pounds of BOD5 per acre of total secondary treatment
stabilization pond surface area per day. The maximum organic loading rate on the first treatment
stabilization pond in the stabilization pond series shall be 75 pounds of BOD5 per acre per day. The
organic loading which is applied to the stabilization ponds is equal to the total influent organic loading
minus any reduction in organic load provided by the primary treatment units.
(6) Inlet/Outlet Structures. All outlets shall be baffled with removable baffles to prevent
floating material from being discharged, and shall be constructed so that the level of the pond surface may
be varied under normal operating conditions. Outlets shall be submerged to a depth between 18 and 24
inches to assist in controlling the discharge of algae. The engineer shall consider the use of multipurpose
control structures to facilitate normal operational functions such as drawdown and flow distribution flow
depth, measurement, sampling, pumps for recirculation, chemical additions, and to minimize the number of
construction sites within embankments. Seep water-stop collars shall be located on all piping embankment
penetrations. All ponds shall have drain piping to allow emptying for maintenance. Pumps may be used
as part of the drainage system if ponds cannot be partially drained by gravity. If not permanently
installed, a temporary piping suction station shall be provided.
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§217.207. Evaporative Ponds.
(a) General. A minimum of two ponds shall be provided for the evaporative pond process. The
primary pond surface area shall be sized to provide approximately 60% of the total surface area required.
Additional secondary ponds may be added, but the 60% primary/40% secondary split shall be maintained.
The number and size of ponds is determined by high and low periods of evaporation. During high
evaporation periods, only the primary pond may be required for effective operations. During low
evaporation wet weather periods, the secondary ponds may be required to provide adequate evaporative
surface area to accommodate the influent flows and precipitation.
(b) Odor Management. Evaporative ponds shall be located so that the local prevailing winds will
be toward uninhabited areas, wherever practical.
(c) Liners. Evaporative ponds shall be constructed with synthetic liners. Synthetic membrane
liners shall have a minimum thickness of 40 mils. The liners shall be designed with an underdrain leak
detection system which shall consist of, at a minimum, a leachate collection and a detection system.
Proper compaction of soils beneath the liner shall be required by the construction specifications. The liner
material shall be capable of receiving constant sunlight without degrading
(d) Configuration/Depth/Loading.
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(1) Ponds may be constructed in round, square or rectangular shapes. The corners of
square and rectangular shaped ponds shall be rounded in order to minimize accumulation of floating
materials.
(2) The depth of a given pond is dependant on its location within the pond system
process. The operating depth for primary ponds shall be a maximum of 5 feet, except that the area
around the inlet shall be designed for solids deposition according to the same criteria as a facultative pond
Secondary pond operating depths shall be a maximum of 8 feet.
(3) Evaporation and Organic Loading. Sizing of evaporation ponds shall be based on the
evaporation rate for a given site and a maximum allowable organic loading rate. The evaporation loss
shall be determined by using the Penman-Monteith Method or a comparable established method. The
sizing of the evaporative ponds shall take into account the influent flows and provide for the effects of the
precipitation occurring from a 25-yr. frequency, one-year rainfall amount in accordance with
§309.20(b)(3)(B) of this title (relating to Land Disposal of Sewage Effluent). If an alternate method is
used to determine the evaporative loss, the method, the sources of the method, and all supporting
calculations and documentation associated with the method shall be included in the final engineering
design report. The maximum organic loading rate on an evaporative pond is dependant on the evaporation
rate and shall be determined based on the best professional judgement of the engineer with the exception
that in no case shall the BOD5 loading on the primary pond exceed 150 pounds of BOD5 per acre of
primary pond surface area per day.
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(e) Embankment. Embankments shall be constructed in accordance with §217.202(5) of this title
(relating to General Design Considerations for Natural Systems).
(f) Inlet/Outlet Structures. The influent line shall terminate into a manhole located along the
embankment edge. The inlet manhole invert shall be constructed a minimum of 6 inches above the
maximum high water level of the primary pond. From the manhole, submerged discharge piping shall be
constructed along and anchored to the bottom of the pond. The inlet discharge piping shall discharge into
a depression near the center of the primary pond. At the point of discharge a concrete apron shall be
provided which prevents scour. The apron shall be at least 2 square feet in surface area and at least 8
inches thick. The concrete shall be of a nature which is resistant to the corrosive effects of a raw
sewage environment. Other materials may be used for the apron provided the material and its suitability
for use in a sewage environment are discussed in the final engineering design report. Inlet and outlet
structures for evaporative ponds shall be constructed in a manner which allows the water surface
elevation to be varied during normal operating conditions.
§217.208. Constructed Wetlands .
Constructed wetlands are man-made complexes of saturated substrates, emergent and
submergent vegetation, animal life, and water designed to simulate natural wetland ecologic conditions.
Constructed wetland are designed to be inundated or saturated by wastewater flow at a frequency and
duration sufficient to support a prevalence of flora and fauna typically adapted for life in wetlands
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conditions. Constructed wetlands described in these rules are intended to function exclusively as
secondary wastewater treatment units. Constructed wetlands may include free water surface systems
(FWS) or subsurface flow systems (SFS). Each of these systems presents special design considerations.
The use of natural wetlands for wastewater treatment is prohibited.
(1) General Design Considerations.
(A) Nitrification. All constructed wetlands intended by the engineer to provide
nitrification shall be considered an innovative and nonconforming technology, and shall be subject to
§217.10(2) of the title (relating to Type of Approval).
(B) Floating Material Removal. Provisions shall be made for the removal of
primary treated effluent algal mat or other floating materials prior to entering the wetlands. Removal
mechanisms may include screens, submerged adjustable inlets, baffles or other methods if deemed
effective by the engineer. The use of covered primary treatment systems, such as Imhoff or septic tanks,
may eliminate the need for algal mat removal. Removed floating material shall be stored and disposed of
in such a manner as to minimize nuisance odors. Similar provisions shall be provided at the wetlands
discharge. Any disposal practices shall not conflict with the requirements in Chapter 330 of this title
(related to Municipal Solid Waste).
(C) Typical Vegetation. Commonly used flora for constructed wetlands include:
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(i) Emergent aquatic vegetation such as Scirpus spp. (bulrush), Sagittaria
spp. (arrowhead), Phragmites spp. (reeds), Juncus spp. (rushes), Elecharis spp. (spikerush), Cyperus spp.
(sedges). Typha spp. (cattails), and various aquatic grass species (e.g. wild rice, etc.). A diverse
vegetative community is recommended to minimize adverse impacts from potential disease, insect pests,
or species specific toxicity.
(ii) Floating aquatic vegetation such as Lemna spp. (duckweed),
Hydrocotyle umbellata spp. (water pennywort), Limnobium spongia spp. (frogbit), Nymphaea spp. (water
lily), Wolffia spp. (water meal), or other appropriate species may be used in conjunction with emergent
plant species.
(iii) The use of indigenous plants is recommended, provided that these
species have been demonstrated as effective for the constructed wetlands wastewater environment.
Plans for harvesting aquatic plants from waters of the state shall be reviewed with the U.S. Corp of
Engineers to determine if permitting or other regulatory coordination is required. Procurement of seed
plants from natural wetlands shall assure minimum impact on the harvested plant community.
(iv) The use of all harmful or potentially harmful wetlands plant and
organisms, as described in 31 TAC 57.111-57.118 and 31 TAC 57.251-57.258, shall first be approved by
the Texas Parks and Wildlife Department. Planned wetlands plant and organisms shall be defined in the
Final Engineering Report.
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(D) Herbicides, insecticides, and fertilizers are prohibited within constructed
wetlands.
(E) Maintenance of emergent and aquatic vegetation in constructed wetlands
may be improved by periodic removal of dead plant matter and detritus. Removal methods shall be
carefully selected to prevent damage to living plants, liners, and system hydraulics. Wetlands plant
maintenance may assist in promoting active growth, controlling of mosquitos, and maintaining hydraulic
capacity. Methods of constructed wetlands maintenance shall not result in a deterioration of water
quality.
(F) Constructed wetlands require time for maturity of flow ecosystems before
effective wastewater treatment may be anticipated. The engineer shall make provisions to ensure that a
properly functioning wetlands system has been developed before wastewater effluent is processed in the
wetlands system. This may be done by including appropriate language in the project specifications and/or
instituting a management and oversight program which considers items such as construction scheduling,
plant species selection, planting practices, and start-up procedures.
(G) Wetlands are subject to significant evaporative losses in warm climate
applications. If the engineer determines that the climate and/or size of the pond are such that evaporative
losses might have a significant impact on the effectiveness of the wetland system, the engineer shall
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perform water balance calculations, determine the potential effect of evaporation on the predicted effluent
concentrations, and include such analyses in the final engineering design report.
(H) Allowed Uses. Free Water Surface and Submerged Flow wetlands may be
used as either secondary treatment units, advanced secondary treatment units, or as a means of polishing
wastewater effluent.
(I) Primary Treatment. All constructed wetlands shall be preceded by primary
treatment. Systems may be preceded by secondary treatment. Primary treatment may include septic
tanks, Imhoff tanks facultative lagoons, aerated lagoons, stabilization ponds, or any other primary
treatment process properly designed to remove settleable and floating solids. Odor and algae control shall
be considered in selecting the primary treatment system. Primary treatment units shall be designed to
normally produce an effluent quality of less than 150 mg/l BOD5 to help minimize anaerobic conditions
and stress of vegetative communities in subsequent wetlands treatment units.
(J) Liners. Liners for wetlands systems shall comply with the requirements of
§§217.202(3) and (4) of this title (relating to General Design Considerations for Natural Systems), except
that synthetic liners shall not be used in wetland systems. A minimum 6-inch layer of productive topsoil
shall be placed above the liner to encourage subgrade root penetration.
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(K) Flood Hazard Analysis. Constructed wetlands shall be protected from flood
hazard in accordance with the requirements of §217.34 of this title (relating to 100-Year Flood Plain
Requirements).
(L) Berms. Constructed wetlands berms shall not be constructed with side
slopes steeper than 3:1. Interior berm sideslopes shall be lined when wetlands design requires lining.
Interior berm sideslopes above the normal operational water level, and exterior berm sideslopes, shall be
finished with a minimum 6-inch productive topsoil layer and vegetated with grass or a comparable natural
erosion control system. An alternate synthetic side slope protection system, such as slope paving, may be
provided.
(M) Wastewater treatment systems which utilize constructed wetlands as the
means of complying with a permit effluent limit shall be sized and designed in a manner which ensures
that the permit limits may be complied with assuming any one constructed wetland cell out of service.
(2) Free Water Surface Systems. FWS wetlands are shallow open water bodies,
normally less than 24 inches water depth, populated principally by various emergent plant species.
Wastewater flows through the wetland, primarily in the horizontal direction, and is treated by a variety of
physical, biological, and chemical treatment processes.
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(A) FWS General Design. FWS wetlands designs shall be based on a maximum
water depth of not greater than 24 inches in emergent vegetated areas at design flow.
(B) FWS Plant Spacing. Spacing of wetland plants during planting will affect
the systems start-up schedule. Plant stocks shall be placed adequately close to assure maturity of the
wetlands flora ecosystem under normal growing conditions before the application of wastewater to the
wetlands. FWS wetlands plant spacing shall be not more than 72 inches on center. The actual plant
spacing shall depend on the site conditions and the plant species selected.
(C) FWS Configuration. FWS wetlands facilities shall include the following
minimum configuration standards.
(i) Multiple Units. The treatment system shall include multiple units,
preferably arranged in parallel, which may be operated independently, allowing individual units to be
removed from service while maintaining system operations. Units shall be sized to meet permit effluent
water quality limits with any single unit removed from service.
(ii) Minimum slope. Wetland cells shall be provided with adequate
bottom slope to facilitate drainage for maintenance. Bottom slope shall be designed to maintain
appropriate wetlands water depth range along the entire wetlands length under all anticipated operational
flow conditions.
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(iii) Parallel trains. Parallel treatment trains shall be provided to increase
operational flexibility.
(iv) Wind protection. Wetland cells shall be oriented to avoid cross
winds perpendicular to the process flow direction, where practical, to avoid undesirable mixing effects.
Elevated berms or vegetative windbreaks may provide an effective alternative to cell orientation.
(D) Flow Distribution. Treatment efficiency for constructed wetlands depends
largely on effective flow distribution and collection. FWS wetlands facilities shall include the following
minimum flow distribution standards.
(i) Uniform distribution. FWS wetlands inlets and outlets shall be
designed to assure uniform distribution of influent flow and uniform collection of effluent flow across the
entire cell cross section. Inlet and outlet devices shall be designed to minimize erosion of wetlands
substrate from locally high velocities. Outlet and inlet devices shall be designed to allow variations in
operational water level.
(ii) Submergence. Inlets shall be submerged under normal operational
conditions. Placement of inlets and outlets in gravel or comparable coverage may help distribute flow,
reduce algal clogging, and prevent intrusion by aquatic plants and animals.
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(iii) Inspection and Cleaning. Provisions shall be made to allow
inspection and cleaning of inlet and outlet devices.
(E) FWS Organic Loading/Treatment Efficiency. Constructed wetlands process
design may normally be based on organic loading design for typical municipal wastewater primary or
secondary effluent. Suspended solids removal efficiency normally does not require separate design
consideration, being equally efficient or more efficient than organic removal efficiency. Organic removal
treatment efficiency for FWS wetlands shall be based on the areal loading rate equation, equation 3.h, or
comparable methods. If an alternate method is used to determine the organic removal treatment
efficiency, the method, the sources of the method and all supporting calculations and documentation
associated with the method shall be included in the final engineering design report. Figure 1:
§217.208(2)(E)
C0 ’C (% (Ci&C ()exp& Ka Equation3.h 0.0365Q
where:
Ci = influent BOD5 concentration, mg/l
Co = target effluent BOD5 concentration, mg/l
C* = wetland background limit, mg/l
(for TSS, C* = 5.1 = 0.16Ci)
(for BOD5, C* = 3.5+ 0.053 Ci)
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k = first-order areal rate constant: (34 m/yr @ 20B C for BOD)
A = is required wetland area, ha (1,000 m/yr @ 20B C for TSS)
(active treatment area, not including dike, buffers, etc.)
Q = is design flow in m3/d
(F) Vector Control. Provisions for mosquito control within FWS wetlands shall
be included as part of the system’s design. Such provisions may include: the use of mosquito fish
(Gambusia) and other natural predators, maintenance of aerobic conditions, and use of biological controls.
The engineer shall take into consideration the potential damage to wetlands caused by mammals such as
nutria and muskrats during the design process.
(3) Subsurface Flow Systems. SFS wetlands are shallow water bodies, normally with a
water depth less than 24 inches, populated by various emergent plant species. Wastewater flow in SFS
wetlands is maintained below the surface of a porous media, such as gravel, in which the emergent plants
are rooted. Wastewater flows through the SFS wetland, primarily in the horizontal direction, and is
treated by a variety of physical, biological, and chemical treatment processes similar to those provided in
FWS wetlands.
(A) SFS General Design. Root penetration into the wetted subsurface media is
a significant design consideration for SFS wetland systems. Treatment efficiency generally improves with
effective root penetration through the entire wetted media depth. Design operational water depth shall not
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exceed 18 inches at design flow, or shall not exceed the maximum normally anticipated root penetration
for the planned primary population emergent plant species, whichever is less. The design shall include
provision for seasonal drawn down of the water level to encourage deeper root penetration into the
wetted media.
(B) SFS Plant Spacing. Spacing of the wetlands plants during planting will
impact system start-up schedule. Plant stocks shall be placed adequately close to assure maturity of the
wetlands flora ecosystem under normal growing conditions, before scheduled wastewater loading. SFS
wetlands plant spacing shall be not more than 36 inches on center. Actual spacing shall depend on the
site conditions and the plant species selected.
(C) SFS Configuration. SFS wetlands facilities shall include the following
minimum configuration standards.
(i) Multiple units. The treatment system shall include multiple units,
arranged in parallel, which may be operated independently, allowing individual units to be removed from
service while maintaining system operations. Units shall be sized to meet permit effluent limits with any
single unit removed from service.
(ii) Hydraulic profile. Hydraulic profile of SFS wetlands may be
significantly steeper than FWS systems. Smaller length to width ratios generally assist effective hydraulic
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profile design. SFS wetlands shall be designed to maintain minimum 6-inch dry media cover during design
flows, at least 2-inches of upstream media cover during 2-hour peak flow conditions, and not more than
12-inches of upstream media cover during diurnal low flow conditions. SFS wetland hydraulic profile
design shall be based on Darcy’s Law, equation 4.h, unless an alternate design method, which includes the
sources of the method and all supporting calculations and documentation associated with the method, is
justified in the final engineering design report. Figure 2: §217.208(3)(c)(ii)
Q’Ks (A(S Equation 4.h
where:
Q = Design flow (gal/day)
KS = Media hydraulic conductivity (gal/sf/day) (see Table H.1
S = Hydraulic gradient (ft/ft)
A = Cross sectional area perpendicular to the flow
Table H.1 - Typical Media Characteristics
Media Effective Size (inches) Porosity (%) Hydraulic Conductivity
(gal/sf/day)
Fine Gravel 5/8" 38 185,000
Medium Gravel 1¼” 40 250,000
Coarse Rock 5" 45 2,500,000
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(iii) Maximum depth. SFS wetlands shall be designed for a maximum
wetted media depth of 24-inches at design flow, or the maximum normally anticipated root penetration for
the planned primary population emergent plant species, whichever is less. A dry media cover depth of 6
to 9 inches shall be provided above the design flow hydraulic gradient.
(iv) Minimum slope. SFS wetland cells shall be provided with adequate
bottom slope to facilitate drainage for maintenance, while maintaining appropriate media water depth and
cover along the entire cell length under all anticipated operational flow conditions.
(v) Parallel trains. Parallel treatment trains shall be provided to increase
operational flexibility.
(D) Flow Distribution. Constructed wetlands treatment efficiency depends
largely on effective flow distribution and collection. SFS wetlands facilities shall include the following
minimum flow distribution standards.
(i) Flow distribution. SFS wetlands inlets and outlets shall be designed to
assure uniform distribution of influent flow and uniform collection of effluent flow across the entire cell
cross section. Inlet and outlet devices shall be designed to minimize transport of wetlands media from
locally high velocities. Outlet and, where necessary, inlet devices shall be adjustable to allow variation in
operational water level and flooding of cells for weed control.
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(ii) Submergence. Inlets and outlets shall be below the media surface
and shall be designed to allow variations in operational water level.
(iii) Maintenance. Provisions shall be made to allow inspection and
cleaning of inlet and outlet devices.
(iv) Staged influent feed. If deemed necessary by the engineer,
provisions for optional staged influent feed to improve process control, particularly where a high influent
BOD5 load is anticipated, shall be included as part of the wetland system’s design.
(E) SFS Organic Loading/Treatment Efficiency. Constructed wetlands process
design may normally be based on organic loading design for typical municipal wastewater primary or
secondary effluent. Suspended solids removal efficiency normally does not require separate design
consideration, being equally efficient or more efficient than organic removal efficiency. Organic removal
treatment efficiency for SFS wetlands may be based on the areal loading equation, equation 5.h. If an
alternate method is used to determine the organic removal treatment efficiency, the method, the sources
of the method and all supporting calculations and documentation associated with the method shall be
included in the final engineering design report. Figure 3: §217.208(3)(E)
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C0 ’C (% (Ci&C ()exp& Ka Equation5.h 0.0365Q
where:
Ci = influent BOD5 concentration, mg/l
Co = target effluent BOD5 concentration, mg/l
C* = wetland background limit, mg/l
(for TSS, C* = 5.1 = 0.16Ci)
(for BOD5, C* = 3.5+ 0.053 Ci)
k = first-order areal rate constant: (180 m/yr @ 20B C for BOD)
A = is required wetland area, ha (3,000 m/yr @ 20B C for TSS)
(active treatment area, not including dike, buffers, etc.)
Q = is design flow in m3/d
(F) Temperature. Winter design condition water temperature for SFS wetlands
are generally warmer than FWS wetlands design due to improved insulation and shorter hydraulic
residence time of SFS wetlands, particularly if upstream treatment processes do not provide significant
heat loss opportunity. This warmer temperature shall be accounted for in the design as deemed
necessary by the engineer.
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(G) Vector Control. Mosquito control is generally not as significant a concern
for SFS wetlands as with FWS systems. Vegetation maintenance practices shall include removal of
excessive plant litter and detritus to prevent mosquito breeding opportunities.
(H) Media Design. SFS wetlands media shall be appropriate for constructed
wetlands wastewater application and shall meet the following minimum requirements.
(i) Media shall be hard rock, slags, or other clean, comparable media
material. Media shall maintain less than 0.1% by weight of clay, sand and other fine materials.
(ii) Rock or mineral media materials shall have a Mohs hardness of at
least 5.0, and all media shall be resistant to acidic conditions.
(iii) Synthetic medias shall be considered nonconforming and/or
innovative technologies and shall be subject to §217.10(2) of this title (relating to Types of Approvals).
(iv) Media gradation and uniformity will determine wetlands hydraulic
conductivity. The executive director shall have the discretion to require a laboratory determination of the
hydraulic gradient for the proposed media.
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(v) Media shall be carefully placed in the SFS wetlands by light
equipment to avoid introduction of clay or other undesirable materials, to avoid compaction, and to avoid
rutting of the subgrade.
(vi) Where a gravel media larger than one and one-half inch diameter is
used in the subsurface flow system, a top layer of small gravel shall be provided to encourage healthy
plant rooting. The gravel layer shall be maintained above the normally saturated media zone. A
transitional (medium grade) layer shall be provided between small gravel caps and coarse gravel to
minimize small gravel migration into lower void spaces.
§217.209. Overland Flow Process.
The overland flow process (O.F.) is the application of wastewater along the upper portion of
uniformly sloped and grass covered land and allowing it to flow in a thin sheet over the vegetated surface
to runoff collection ditches. The primary objective of this process is treatment of wastewater. Utilization
of this process does result in a discharge; therefore, a wastewater discharge permit from the commission
is required. This process is best utilized on soils with low permeability. The performance of the overland
flow process is dependent on the detention time of the wastewater on the vegetated sloped area. In order
to meet a specified effluent criteria, the hydraulic loading rate, the application rate, and the effectiveness
of the distribution system are essential design considerations.
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(1) Nitrification. All overland flow processes, which are intended by the engineer to
provide nitrification, shall be considered an innovative and nonconforming technology, and shall be subject
to §217.10(2) of this title (relating to Types of Approvals).
(2) Design Constraints. All overland flow processes shall at a minimum be preceded by
a bar screen and one of the primary treatment options detailed in §§217.203-217.205 of this title (relating
to Imhoff Tanks, Facultative Ponds, and Aerated Ponds) and §§217.138 (i) and (j), of this title (relating to
Primary Clarifiers-Design Basis, Primary Clarifiers-BOD5 Removal and Primary Clarifiers-Sludge
Pumping and Piping). Except as stated in this section, the overland flow process may only be used as a
means of providing sufficient secondary treatment to comply with a permit with the following effluent
sets: 10 mg/l BOD5 and 15 mg/l TSS; 20 mg/l BOD5 and 20 mg/l TSS; or 30 mg/l BOD5 and 90 mg/l
TSS.
(3) Hydraulic Loading Rate. The hydraulic loading rate and application rate may vary
depending on levels of pretreatment, desired quality of effluent, temperature, and other climatic conditions.
Table H.2 provides suggested values for application rates. The design rates selected and their justification
shall be included in the final engineering design report. In no case shall an application rate greater than
0.5 gallons per minute per foot of slope be used. Figure 1:§217.209(3)
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Table H.2 - Suggested Application Rates for Overland Flow Systems - *
Process Conditions Application Rate (gallons/minute/foot of slope)
Overland Flow
Preceded by Primary Treatment
Permit Limits: 30 mg/l BOD5
90 mg/l TSS
Maximum Soil Temperature > 10EC
0.16
Overland Flow
Preceded by Primary Treatment
Permit Limits: 30 mg/l BOD5
90 mg/l TSS
Maximum Soil Temperature < 10EC
0.13
Overland Flow
Preceded by Primary Treatment
Permit Limits: 20 mg/l BOD5
20 mg/l TSS
Maximum Soil Temperature > 10EC
0.13
Overland Flow
Preceded by Primary Treatment
Permit Limits: 20 mg/l BOD5
20 mg/l TSS
Maximum Soil Temperature < 10EC
0.12
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Overland Flow
Preceded by Primary Treatment
Permit Limits: 10 mg/l BOD5
15 mg/l TSS
Maximum Soil Temperature > 10EC
0.12
Overland Flow
Preceded by Primary Treatment
Permit Limits: 10 mg/l BOD5
15 mg/l TSS
Maximum Soil Temperature < 10EC
0.09
Overland Flow
Preceded by Secondary Treatment
0.19
* - Numbers are based on the EPA’s Process Design Manual EPA/625/1-81/013a titled Supplement on Rapid Infiltration and
Overland Flow
(4) Climate/Wastewater Storage. Temperature significantly affects treatment
performance. As temperatures approach 0°C (32°F), treatment performance deteriorates, particularly for
nitrogen removal. At temperatures below freezing, ice may form on the terraces causing the applied
wastewater to run over the ice. The wastewater will not contact the soil, and treatment will cease.
Storage is, therefore, needed for the wastewater for days when temperatures preclude operation.
Precipitation is not a significant factor with respect to treatment performance as effluent BOD5 and TSS
concentrations increase only slightly during rainfall events. The additional runoff generated by the rainfall
greatly increases the mass of these pollutants’ discharge limits; therefore, provisions shall be made to
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store influent wastewater during rainfall sufficiently to ensure compliance with the organic load mass
limits in the discharge permit. The number of days of storage required for the overland flow process shall
be determined by the engineer with the provision that the minimum number of days of storage shall be 2
days.
(5) Storage Basin Design. To minimize the impact of algae on the treatment
performance, storage basins shall be designed as off-line basins, used only as needed, and emptied as
soon as possible by blending with other pretreated wastewater prior to application.
(6) Storage Basin Construction. Any storage basins constructed as part of an overland
flow system shall comply with §§217.202(3)-(5) and 217.206(6) of this title (relating to General Design
Considerations for Natural Systems and Wastewater Stabilization Ponds).
(7) Nuisance Odor Prevention. The engineer shall determine if odors from any portion
of the overland flow system will be a nuisance to adjacent landowners. If the engineer determines that
the overland flow system will be a nuisance to adjacent landowners, the design shall include sufficient
measures to prevent the nuisance odors.
(8) Soil/Soil Testing. Overland Flow systems shall be allowed only in soil conditions
which will not allow any effluent percolation to groundwater. Overland flow systems shall not be
allowed in soils which have a coefficient of permeability greater than 0.6 inches per hour. Core samples
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shall be taken at sites where overland flow systems are proposed, and a soil profile and a permeability test
shall be performed for these cores. The number of cores which shall be analyzed shall be at least 10
cores, or one core for each two acres, whichever is greater. Additionally, a geological investigation shall
be done which determines the depth to groundwater and the depth to bedrock under the overland flow
site. The soil profile evaluation shall extend to a depth of at least 4 feet below the root zone of the
vegetation in the overland flow system. Deeper soil profiles and further hydraulic and geological
analyses may be required at the discretion of the executive director to ensure that the overland flow
system does not constitute a threat to groundwater. All testing results and geological information shall be
included in the final engineering design report.
(9) Distribution Systems. The method of application shall achieve and maintain uniform
coverage of the overland flow area onto and across the terraces. The application cycle shall provide a
maximum of 12 hours for dosing followed by a minimum period of 12 hours of resting.
(10) Terraces. The sloped areas to receive wastewater shall be uniformly graded to
eliminate wastewater ponding and short circuiting for the length of the flow. Site grading procedures and
tolerances shall be included in the specifications. Minimum slopes shall equal or exceed 2 percent;
maximum slope shall not exceed 8 percent. The application site shall be protected from flooding. The
minimum slope length for the applied wastewater shall be 100 feet.
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(11) Vegetation Selection. A vegetative cover shall be provided on the application site.
The plant types selected shall be suitable for overland flow conditions and shall provide uniform coverage
of soil to prevent short circuiting and channelization of the area.
(12) Buffer Zone. The overland flow process treatment area shall be subject to the
same buffer zone requirements as aerobic wastewater treatment system units.
(13) Disinfection. Wastewater quality and disinfection requirements for overland flow
process discharges will be established by the discharge permit.
(14) Sampling. An effluent sampling station shall be provided prior to discharge to
surface waters. The sampling and reporting requirements will be established by the discharge permit.
§217.210. Integrated Facultative Ponds.
Integrated facultative ponds shall be considered nonconforming technology. If a review of an
integrated facultative ponds is performed by the executive director, the review will be done in accordance
with §217.10(2) of this title (relating to Types of Approvals) and the criteria described in this section.
(1) Configuration/Inlets/Outlets. The length-to-width ratio of the facultative pond shall
be three to one (3:1), but other dimensions more suitable to the site may be used upon justification by the
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design engineer. The inlet shall be located in the pit portion of the pond. The pit shall not be less than
0.40 acres in total surface area, and the outer pond area, shall not be less than 10 times the surface area
of the pit. The pit shall be sized with a volume adequate to contain 0.1 cubic feet per capita per year
sludge storage (minimum 20-year design period) plus a two day hydraulic retension time above the sludge
storage area. The upflow velocity in the pit shall not exceed two feet per day at design flow. More than
one pit may be located within a single integrated facultative pond as long as each pit receives an
equivalent amount of wastewater influent. The outlet shall be constructed so that the water level may
vary by no more than one (1) foot. The engineer shall locate facultative ponds in a central location with
regard to the surrounding secondary ponds to facilitate compliance with the buffer zone requirements
specified in Chapter 309 of this title (relating to Domestic Wastewater Effluent Limitations and Plant
Siting).
(2) Depth. The inlet pit shall not be less than 15 feet deep from the water surface
elevation during normal operating conditions to the influent inlet point within the pit. For the integrated
facultative pond, berms or other deflection devices, at least 5 feet high or one-half the depth of the outer
pond, whichever is less, shall be constructed around the pit within the integrated facultative pond. The
depth from the water surface elevation during normal operating conditions, to the top of the berm around
the pit, shall be at least 5 feet.
(3) Organic Loading. The organic loading shall be no more than 300 pounds of ultimate
BOD per acre of total pond area per day into the pit.
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(4) Odor Control. Odor shall be controlled by placing the inlet to the pit(s) 3 feet above
the bottom of the pond with the flow directed downward. Furthermore, water from the next stage pond
following the facultative pond shall be recirculated to the surface of the integrated facultative pond.
Capabilities for recirculation at 50% to 100% of the design flow shall be provided for the facultative
pond(s), from the outlet of the downstream pond. Facultative ponds shall be designed to preclude
situations where siphoning of pond contents through submerged inlets may occur.
(5) Removal Efficiency. In the integrated facultative pond removal efficiency may be
assumed to be up to 60% of the influent BOD5 in the pit portion of the integrated facultative pond.
Subsequent removal of BOD5 within the outer portion of the integrated facultative pond may be assumed
to be up to 50% of the remaining 40%. A minimum of 21-days hydraulic retention time shall be provided
in the integrated facultative pond.
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SUBCHAPTER J : SLUDGE
§§217.240-217.252
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.240. Applicability.
This subchapter establishes the minimum design requirements for sewage sludge treatment
processes and treatment units. For purposes of this rule, sludge process is assumed to include thickening,
stabilization, and dewatering. The selection and operation of the sewage sludge unit processes shall be
based on the ultimate utilization of the final sludge product. All municipal wastewater treatment facilities
that dispose of sludge under Chapter 312 (relating to Sludge Use, Disposal, and Transportation) shall use
stabilization. All municipal wastewater treament facilities that dispose of sludge under Chapter 330
(relating to Municipal Solid Waste) shall comply with the requirements of that chapter.
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§217.241. Control of Sludge and Supernatant Volumes.
Provisions shall be made for the return of supernatant, or centrate, resulting from sludge
processing activities to the head of the treatment works, discharged at a point preceding the aeration
system, or preceding the secondary treatment unit(s) if no aeration exists at the plant. Digester
supernatant liquor volume shall be minimized to the greatest extent practical. The impact of the returned
supernatant on the downstream units shall be accounted for in the unit designs.
§217.242. Sludge Piping.
Any sludge piping included as part of the sludge processing facilities shall have sufficient gradient
to insure the flow of sludge. Piping under stationary structures shall be arranged so that stoppages may
be readily eliminated by rodding or with sewer cleaning devices. Gravity piping shall be laid on uniform
grade and alignment. Slopes on gravity discharge piping shall not be less than three percent. Sludge
piping within digesters, including sludge drain lines, shall be a minimum of four inches in diameter. Sludge
withdrawal piping for anaerobic digesters and gravity thickeners shall have a minimum diameter of 6
inches for gravity withdrawal and 4 inches for pump suction and discharge lines. Where withdrawal is by
gravity, the available head on the discharge pipe shall be at least four (4) feet. Also, where gravity
withdrawal is to be used as the primary withdrawal method, the piping design for the primary sludge
clarifier pump shall allow the pump to be used for removal of digested sludge. Sludge piping shall include
a means to observe the quality of the supernatant from each of the withdrawal outlets provided. All
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sludge processing and treatment units shall be capable of being drained independently of one another.
Special consideration shall be given to the corrosion resistance and continuing stability of supporting
systems for piping located inside the digestion tank.
§217.243. Sludge pumps.
The engineer shall select sludge transfer pumps based on both the quantity and character of the
anticipated solids load to be handled by them. Where mechanical pumps are used, a sufficient number of
pumps shall be provided so that the design pumping capacity is available with the largest sludge pump out
of service. Air lift pumps are an acceptable mechanism for sludge transfer. Duplicate design pumping
capacity is not required when air lift pumps are used. Pumps used for pumping sludge shall be specifi
cally designed for that purpose. Centrifugal sludge pumps shall have a positive suction head unless the
pumps are self-priming or equipped with some other priming device. Positive displacement pumps or
other types of pumps with demonstrated solids handling capability shall be provided for handling raw
sludge. The minimum positive head necessary for proper operation shall be provided at the suction side of
centrifugal type pumps. A positive head of 24 inches or more may be desirable for all types of sludge
pumps. Maximum suction lifts shall not exceed 10 feet for positive displacement pumps.
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§217.244. Exclusion of Grit and Grease from Sludge Treatment Units.
The design of the wastewater facility shall minimize, to the greatest extent possible, the discharge
of grit, debris, oil, or grease to the sewage sludge treatment units. The ultimate use and disposal of the
various solids generated during the treatment of domestic sewage shall be included in the design of the
treatment facility. If the sewage sludge is to be land applied, all screening, grit, and grease shall be
removed from the treatment process and disposed of separately from the land applied sewage sludge.
§217.245. Ventilation.
Any sludge treatment or processing areas, where the presence of fumes or gases of a level
sufficient to constitute a public health hazard or a threat to air quality, shall be provided with sufficient
ventilation to eliminate these dangers. Where such conditions exist in an enclosed area, mechanical
ventilation shall be utilized. The mechanical ventilation may be either continuous or intermittent. At a
minimum, the ventilation, if continuous, shall provide at least six complete air changes per hour. If
intermittent, shall provide at least 30 complete air changes per hour. A higher air exchange rate may be
necessary as determined by the engineer. Where such conditions exist in an area which is not enclosed,
the facility design shall include a means of ventilation which protects public health and air quality.
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§217.246. Odor Control.
The design of all sewage sludge process units shall be designed to minimize or eliminate nuisance
odors. If nuisance odors are likely, provisioins for abatement of these odors shall be considered.
§217.247. Chemical Pretreatment of Sludge.
Chemical addition to enhance solids removal is necessary for many sludge treatment or
processing units. This section contains the minimum criteria for the use and handling of chemicals and
equipment.
(1) Chemical Selection. Chemicals shall be compatible with the unit operation and shall
have no detrimental effect upon receiving waters. Pilot plant studies or data from unit operations treating
design flows of sewage or domestic waste waters of similar characteristics (organic levels, metal
concentrations, etc., within 25% of proposed design) shall be used to determine appropriate chemicals and
feed ranges.
(2) Safety Provisions for Storage of Chemicals. Liquid chemical storage tanks shall
include a liquid level indicator and have an overflow and a receiving basin or drain capable of complete
retention of accidental spills or overflows. Powdered activated carbon shall be stored in an isolated
fireproof area. Explosion proof electrical outlets, lights, and motors shall be used in all storage and
handling areas where potentially volatile chemicals or conditions exist. Chemicals shall remain contained
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during transport, storage, and use sufficiently to preclude discharges to the atmosphere. For each
operator who will handle dry chemicals which are known to pose potential health problems resulting from
human exposure, protective equipment for eyes, face, head, and extremities shall be provided. Facilities
shall be provided for eye washing and showering. Protective equipment and neutralizers shall be stored in
the operating area.
(3) Minimum Chemical Supply. Space shall be provided where at least thirty (30) days
of chemical supply may be stored in dry storage conditions, at a location that is convenient for efficient
handling. The chemical supply may be reduced if the final engineering design report includes information
which verifies that such storage may be reduced without limiting the dependability of the necessary
supply. Solution storage tanks or direct feed day tanks shall have sufficient capacity for daily operation at
the design flow of the facility.
(4) Chemical Handling. Provisions shall be made for measuring quantities of chemicals
used to prepare feed solutions. Storage tanks, pipe lines, and equipment for liquid chemicals shall be
specific to the chemicals and not for alternates. Different chemicals shall not be fed, stored, or handled in
such a manner that intermixing of such chemicals could occur during routine treatment operations.
Concentrated liquid acids shall not be handled in open vessels, but shall be pumped in undiluted form from
the original containers to the point of treatment, to a covered day tank, or to a storage tank. Concentrated
acid solutions or dry powder shall be kept in closed, acid-resistant shipping containers or storage units.
Transfer of toxic materials shall be controlled by positive actuating devices. One or more of the control
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methods in subparagraphs (A)-(C) of this paragraph shall be utilized to ensure that the transfer of dry
chemicals from shipping containers to storage bins or hoppers is done in a way which minimizes the
quantity of dust which may enter the equipment room. Provisions shall be made for disposing of empty
containers in a manner which precludes the potential for harmful exposure to chemicals.
(A) Vacuum pneumatic equipment of closed conveyor systems.
(B) Facilities for emptying shipping containers in special enclosures.
(C) Exhaust fans and dust filters which put the hoppers or bins under negative
pressure sufficient to eliminate chemical particles which escape into the air.
(5) Housing of Chemicals. Structures, rooms, and areas accommodating chemical feed
equipment shall provide convenient access for servicing, repair, and observation of operations. Floor
surfaces shall be smooth, slip resistant, impervious, and well drained with a minimum slope of 1/8 inch per
foot. Open basins, tanks, and conduits shall be protected from chemical spills or accidental drainage.
(6) Feed Equipment.
(A) Redundancy. Sufficient equipment redundancy shall be provided to ensure
process dependability during the shutdown of the largest operational unit. A minimum of two feeders shall
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be provided. Feeders shall be able to supply, at all times, the amounts of chemicals needed for process
reliability, at an accurate rate, throughout the range of feed.
(B) Design and Capacity. Proportioning of chemical feed to the rate of flow
shall be provided where the flow rate is not constant. Positive displacement type solution feed pumps
shall not be used to feed chemical slurries unless justified by the engineer in the final engineering design
report. The treatment works’ potable water supply shall be protected from contamination by chemical
solutions or sewage by providing an air gap between the supply line and the solution tank. Materials and
surfaces shall be resistant to the chemical solution(s) which they will come into contact with. Dry
chemical feeder systems shall measure chemicals volumetrically or gravimetrically; provide effective
mixing and solution of the chemical in the solution pot; provide gravity feed from solution pots, if possible;
completely enclose chemicals; and prevent emission of dust to the operation room.
(C) Location. Feed equipment shall be located near the points of application to
minimize length of feed lines and shall be readily accessible for servicing, repair, and observation. Feed
equipment shall be provided with protective curbing so that chemicals from equipment failure, spillage, or
accidental drainage will be contained.
(D) Control. Feeders shall be automatically controlled. The automatic control
shall be capable of reverting to manual control. The feeders shall be manually started. Automatic
chemical dose or residual analyzers shall be used as deemed necessary by the engineer. Where
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automatic chemical dosing or residual analyzers are used, the engineer shall determine the need for
alarms for critical values and recording charts.
(E) Weighing Scales. Weighing scales shall be provided for volumetric dry
chemical feeders. The scales shall accurately measure increments of 0.5 percent of load. Weighing
scales shall be provided for weighing of carboys which are not calibrated volumetrically.
(F) Feeder System Protection. The entire feeder system shall be protected
against freezing and shall be readily accessible for cleaning.
(G) Service Water Supply. Water used in the feeder system shall be protected
from contamination. The service water shall be ample in supply and have sufficient pressure to ensure
dependable operations. The water supply shall include a means for measurement when preparing specific
solution concentrations. Where a booster pump is required, sufficient duplicate equipment to ensure
process reliability shall be provided.
(7) Solution Tanks. Means shall be provided to maintain uniform strength of solution
consistent with the nature of the chemical solution. Continuous agitation shall be provided to maintain
slurries in suspension. Two (2) solution tanks shall be required for a chemical to assure continuity of
chemical application during servicing. The total tank capacity shall provide storage for at least one full
day of operation at design flow. Each tank shall be provided with a drain. Means shall be provided to
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indicate the solution level in the tank. Make-up potable water shall enter the tank through an air gap.
Chemical solutions shall be kept covered with access openings curbed and fitted with tight covers.
Subsurface locations for solution tanks shall be completely impermeable, protected against buoyancy
forces, include provisions to drain groundwater or other accumulated water away from the tank, include
design provisions which will detect leaks, and allow for containment and remediation of any chemical
leaks, spills or overflows. Overflow pipes shall be turned downward, have free discharge, and be placed
in the most practical location which is most likely to be noticed during normal maintenance and operation
of the facilities. The overflow pipes shall not contaminate the wastewater or receiving stream and shall
not constitute a hazard to operating personnel.
(8) Requirements for Chemical Application. Chemical application shall assure
maximum efficiency of treatment and provide maximum safety to operators. Chemical application shall
also assure satisfactory mixing of the chemicals with the sludge. Chemicals shall be applied in a manner
which prevents backflow or back-siphonage between multiple points of feed through common manifolds.
The application of pH affecting chemicals to the wastewater shall be done prior to the addition of
coagulants.
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§217.248. Sludge Thickening.
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Sludge thickening is used for volume reduction and conditioning of sludge, prior to sludge
treatment, as an aid to processing and managing the sludge waste stream. Sludge thickening is not
required. If sludge thickeners are used, the following criteria shall apply.
(1) General Requirements for Thickeners.
(A) Capacity. Thickeners shall be designed to operate effectively during the
two-hour peak flow.
(B) Flexibility. A bypass around the thickening process shall be provided. Dual
units, alternate means of thickening, alternte disposal methods or adequate storage shall be provided for
all treatment works whose design flow is greater than 1.0 mgd capacity.
(2) Specific Requirements for Mechanical (Gravity) Thickeners.
(A) Equipment Features. Mechanical thickeners shall employ low speed stirring
mechanisms for continuous mixing and flocculation within the zone of sludge concentration. The
mechanical thickener shall be designed to provide for sludge storage, if sufficient storage is unavailable
within other external tankage. A means of controlling the rate of sludge withdrawal shall be provided.
The scraper mechanical train shall be capable of withstanding all expected torque loads. The normal
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working torque load shall not exceed ten (10%) of the rated torque load. Chemical addition and dilution
water feed systems may be used to optimize performance.
(B) Design Basis. The basis of design shall be detailed in the final engineering
design report. The executive director shall have the discretion to require data obtained from a pilot study.
Thickener overflow rates shall be 400-800 gpd/sf. The side water depth shall be a minimum of 10 ft.
Circular thickeners shall have a minimum bottom slope of 1.5 in/ft. The scraper mechanism peripheral
velocity shall be 15 to 20 ft/min. The thickener shall be designed to minimize short circuiting.
(3) Specific Requirements for Dissolved Air Flotation Thickeners.
(A) Equipment Features. Dissolved air flotation (DAF) basins shall be equipped
with bottom scrapers to remove settled solids. The bottom scraper shall function independently of the
surface skimmer mechanism. The recycle pressurization system shall utilize DAF effluent or secondary
effluent in lieu of potable water. A polymer feed system shall be provided. The feed system shall meet
the requirements of §217.247(6) of this title (relating to Chemical Pretreatment of Residuals). Dissolved
air flotation units shall be enclosed in a building. A positive air ventilation system shall be provided.
(B) Design Basis. The basis of design shall be detailed in the final engineering
design report. The executive director shall have the discretion to require data obtained from a pilot study.
Hydraulic loading rates shall not exceed 2.0 gal/min/sq.ft. The solids loading rate shall be 1.0 to 4.0
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lb/hr/sq.ft. The air to solids weight ratio shall be 0.02 to 0.04. The retention tank system shall provide a
minimum pressure of 40 psig. The skimmer shall be designed for multiple or variable speeds. The speeds
shall allow an operational range from one (1) fpm up to 25 fpm.
(4) Specific Requirements for Centrifugal Thickeners. The basis of design shall be
detailed in the final engineering design report. The executive director shall have the discretion to require
data obtained from a pilot study. The centrifuge shall be preceded by pretreatment to prevent plugging of
the nozzle and/or excessive wear in the bowl. Centrate shall be handled in the same way as supernatant
and shall be subject to §217.241 of this title (relating to Control of Sludge and Supernatant Volumes).
§217.249. Sludge Stabilization.
The design requirements for the stabilization processes listed below are based on the assumption
that the process is the sole stabilization process employed at the treatment works. If technically justified in
the final engineering design report, consideration will be given to reducing some of these requirements for
treatment works employing series operation of two or more stabilization processes or methods.
(1) Anaerobic Digestion.
(A) Multiple Design. For facilities with a design flow exceeding 0.5 mgd, a
minimum of two anaerobic digesters shall be provided, so each digester may be used as a first stage or
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primary reactor for treating primary and secondary sludge flows generated at the treatment works.
Where multiple digesters are not provided, a storage basin shall be provided for emergency use, so the
digester may be taken out of service without unduly interrupting treatment works operations. Where
multiple digesters are required, each digester shall have the means for transferring a portion of its
contents to other digesters.
(B) Depth. The anaerobic digester shall provide a minimum of six feet of
storage depth for supernatant liquor.
(C) Maintenance Provisions. The design shall allow for safe access to all units
and appurtenances which may require cleaning, emptying, or maintenance.
(D) Slope. The digester bottom shall slope to drain towards the withdrawal pipe.
Flat-bottomed digestion chambers shall not be used.
(E) Access Manholes. At least two access manholes shall be provided in the
top of the digester, in addition to the gas dome. One opening shall be large enough to permit the use of
mechanical equipment to remove grit and sand. A separate side wall manhole shall be provided at ground
level.
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(F) Safety. The operation and maintenance manual shall specify non-sparking
tools, rubber soled shoes, safety harness, gas detectors for inflammable and toxic gases, and at least one
self contained breathing apparatus.
(G) Sludge Inlets and Outlets. Multiple sludge inlets, draw-offs, and multiple
recirculation section and discharge points (minimum of three) to facilitate flexible operation and effective
mixing of the digester contents shall be provided. One inlet shall discharge above the liquid level and be
located at approximately the center of the digester to assist in scum breakup. Raw sludge inlet discharge
points shall be located to minimize short circuiting to the supernatant draw-off.
(H) Digester Capacity. Where the composition of the sewage has been
established, digester capacity shall be computed from the volume and character of the sludge to be
digested. The total digestion volume shall be determined by rational calculations based upon such factors
as volume of sludge added, the percent solids and character of the sludge, the temperature to be
maintained in the digesters, the degree or extent of mixing to be obtained, and the size of the installation
with appropriate allowance for sludge and supernatant storage. These detailed calculations shall be
included in the final engineering design report to justify the basis of design. The digester shall be capable
of maintaining a minimum average sludge digestion temperature of thirty five degrees Celsius (35o C) (95o
F) with the capability of maintaining temperature control within a 4o(+/-) C range. The design average
detention time for sludge undergoing digestion for stabilization shall be a minimum of 15 days within the
primary digester, but longer periods may be required to achieve the necessary level of pathogen control
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and vector attraction reduction necessary for the method used for sludge management (30 TAC Chapter
312). If unheated digesters are utilized, they shall have the capacity to provide a minimum detention time
of 60 days within the digestion volume in which sludge is maintained at a temperature of at least 20o C
(68o F) (30 TAC Chapter 312).
(i) Completely Mixed Systems. For digesters providing for intimate and
effective mixing of the digestion volume contents, the systems shall be designed for an average feed
loading rate of less than 200 pounds of volatile solids per 1,000 cubic feet of volume per day in the active
digestion volume. Confined mixing systems where gas or sludge flows are directed through vertical
channels, mechanical stirring or pumping systems and unconfined continuously discharging gas mixing
systems shall be designed to insure complete tank turnover every 30 minutes. For tanks over 60 feet in
diameter, multiple mixing devices shall be used. The minimum gas flow supplied for complete mixing shall
be 15 cubic feet per minute per 1,000 cubic feet of digestion volume. Flow measuring devices and
throttling valves shall be used to provide the minimum gas flow. The power supplied for mechanical
stirring or pumping type complete mixing systems shall be a minimum of 0.5 horsepower per 1000 cubic
feet of digestion volume.
(ii) Moderately Mixed Systems. For digestion systems where mixing is
accomplished only by circulating sludge through an external heat exchanger, the system shall be loaded at
less than 40 pounds of volatile solids per 1,000 cubic feet of volume per day in the active digestion
volume. The design volatile solids loading shall be established in accordance with the degree of mixing
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provided. Where mixing is accomplished by other methods, loading rates shall be justified in the final
engineering design report. Where low speed mechanical mixing devices are specified, more than one
device shall be provided unless other mixing devices are also provided.
(I) Gas Collection, Piping, Storage and Appurtenances.
(i) General Requirements. All portions of the gas system including the
space above the liquid surface in the digester, storage facilities, and piping shall be designed so that,
under all normal operating conditions including sludge withdrawal, the gas will be maintained under
positive pressure.
(ii) Safety Equipment. Pressure and vacuum relief valves and flame
traps, and automatic safety shut-off valves shall be provided in all cases where lack of such features
presents safety hazards. INSTALLATION OF WATER SEAL EQUIPMENT ON GAS PIPING IS
PROHIBITED.
(iii) Gas Piping and Condensate. Gas piping shall be adequate for the
volume of gas to be handled and shall be pressure tested for leakage (at 1.5 times the design pressure)
before the digester is placed into service. All gas piping shall slope at least 1/8 inch per foot to provide
drainage of condensation in the gas piping. The main gas line from the digester shall have a sediment trap
equipped with a drip trap. THE USE OF FLOAT CONTROLLED CONDENSATE TRAPS IS
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PROHIBITED. Condensation traps shall be placed in accessible locations for daily servicing and
draining. Drip traps shall be provided at all other low points in gas piping. The gas piping to every gas
outlet, including the pilot line to the waste gas burner, shall be equipped with flame checks or flame traps.
A natural or bottled gas source shall be utilized for the burner pilot. Flame traps with fusible shut-offs
shall be included in all main gas lines. The gas line to the waste gas burner shall include a suitable
pressure, vacuum, and relief valve.
(iv) Electrical Fixtures and Equipment. The electrical equipment
provided in sludge digester pipe galleries containing gas piping shall be designed and installed to eliminate
potential explosive conditions.
(v) Waste gas. Waste gas burners shall be readily accessible and shall
be located at least 50 feet away from any structure, if placed at ground level. Gas burners may be located
on the roof of the control building if sufficiently removed from the digester. Waste gas burners shall not
be located on top of the digester. In remote locations, discharge may be permissible for small quantities of
digester gas (less than 100 CFH) to the atmosphere through a return bend screened vent terminating at
least 10 feet above the walking surface provided the assembly incorporates a flame trap.
(vi) Ventilation. Any underground enclosures connected with anaerobic
digesters tanks, containing sludge, gas piping, or equipment shall be provided with forced ventilation in
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accordance §217.245 of this title (relating to Ventilation). Tightly-fitting, self-closing doors shall be
provided at connecting passageways and tunnels to minimize the spread of gas.
(vii) Meter. A gas meter with bypass shall be provided to meter total
gas production.
(viii) Manometers. Gas piping lines for anaerobic digesters shall be
equipped with closed-type indicating gauges. These gauges shall read directly in inches of water.
Normally, three gauges will be provided: one to measure the main line pressure, a second to measure the
pressure to gas-utilization equipment, and the third to measure pressure to waste burners. Gas tight shut
off and vent cocks shall be provided. The vent piping shall be extended outside the building, and the
opening shall be screened and arranged to prevent the entrance of rainwater. The engineer shall
determine what safety devices and/or appurtenances are needed for the manometer piping system and
shall provide such safety items.
(J) Digestion Temperature Control.
(i) Insulation. Digester shall be constructed above the water table and
shall be suitably insulated to minimize heat loss.
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(ii) Heating Facilities. Sludge shall be heated by circulating the sludge
through external heaters. Unless effective mixing is provided within the digester, piping shall be designed
to provide for the preheating of feed sludge before introduction to the digesters. Provisions shall be made
in the layout of the piping and valving to facilitate cleaning of these lines. Heat exchanger sludge piping
shall be sized for heat transfer requirements.
(iii) Heating Capacity. Sufficient heating capacity shall be provided to
consistently maintain the design temperature required for sludge stabilization. For emergency usage, an
alternate source of fuel shall be available, and the boiler or other heat source shall be capable of using the
alternate fuel.
(iv) Mixing. Facilities for mixing the digester contents shall be provided.
(v) Sludge Heating Device Location. Sludge heating devices with open
flames shall be located above grade in areas separate from locations of gas production or storage.
(K) Supernatant Withdrawal.
(i) Piping Size. Supernatant piping shall not be less than 6 inches in
diameter.
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(ii) Withdrawal Arrangements. Piping shall be arranged so that
withdrawal may be made from three or more levels in the tank. A positive, un-valved, vented overflow
shall be provided. On fixed cover digesters, the supernatant withdrawal level shall preferably be selected
by means of interchangeable extensions at the discharge end of the piping. If a supernatant selector is
provided, provision shall be made for at least two other draw-off levels located in the supernatant zone of
the digester in addition to the un-valved emergency supernatant draw-off pipe. High pressure backwash
facilities shall be provided.
(iii) Sampling. Provisions shall be made for sampling at each
supernatant draw-off level. Sampling pipes shall be at least 1.5 inches in diameter.
(iv) Supernatant Handling. Problems associated with digester
supernatant, such as shock organic loads, shall be addressed in the treatment works design and detailed in
the final engineering design report. Supernatant liquor from anaerobic digesters may be treated by chemi
cal means or other acceptable methods, before being returned to the plant. If the commonly used method
of dosing with lime is employed, the following criteria shall apply: lime shall be applied to obtain a pH of
11.5; the lime feeder shall be capable of feeding 2,000 mg/l of hydrated lime or its equivalent; the lime
shall be mixed with the supernatant liquor by a rapid mixer or by agitation with air in a mixing chamber;
and, after adequate mixing, the solids shall be allowed to settle. The supernatant liquor treatment system
may be a batch or continuous process. If a batch process is used, the mixing and settling may be in the
same tank. The sedimentation tank shall have a capacity to hold 36 hours of supernatant liquor, but not
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less than 1.5 gallons per capita. If a continuous process is used, the sedimentation tank shall have a
detention time of not less than eight hours. Solids settled from the supernatant liquor treatment are to be
returned to the digester or conveyed to the sludge handling facilities. The clarified supernatant liquor shall
be returned to the head of the treatment works in accordance with §217.241 of this title (relating to
Control of Sludge and Supernatant Volumes).
(L) Digester Covers. Uncovered anaerobic digesters shall not be constructed
or used. The sludge and supernatant withdrawal piping for all single-stage and first-stage digesters with
fixed covers shall be arranged in a manner which minimizes the possibility of air being drawn into the gas
chamber above the liquid in the digester. All digester covers shall include a gas chamber adequate for the
gas production anticipated. Digester covers shall be gas tight and the specifications shall require a test of
every digester cover for gas leakage. Digester covers shall be equipped with an air vent which includes a
flame trap, a vacuum breaker, and a pressure relief valve.
(2) Aerobic Sludge Digestion. This subsection applies to the stabilization of waste sludge
to a Class B Biosolid by aerobic digestion. If sludge is not to be digested to a Class B Biosolid, 15 days
of solids storage shall be provided.
(A) Solids Management. A solids management plan shall be prepared by the
engineer, and included in the final engineering design report, which demonstrates a method of managing
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the waste solids which will provide adequate stabilization and adequate volume to maintain the design
sludge age for the biological process.
(B) Detention Time and Mass Balance Requirements. Aerobic digestion is
sensitive to changes in temperature, so the engineer shall use the lowest one week average of the water
temperature for the design temperature of the aerobic digester system. The lowest one week average is
the lowest daily average of seven consecutive days. In addition to designing for the total detention time,
mass balance calculations shall be done. The mass balance calculations shall take into account process
design sludge age, waste stream concentration, operational hours, operational volume in tanks, decant or
dewatering volumes and characteristics, time frames needed for decanting or dewatering, and the volume
needed for storage and sampling.
(i) Single Stage. Single stage aerobic digestion consists of utilizing one
(1) tank operating in continuous-mode-no supernatant removal, continous mode feeding-batch removal, or
other mode as detailed in the solids management plan. The minimum total detention times, based on the
water temperature which shall be used to size aerobic digesters, are provided in Table J.1. The digester
size shall be of sufficient volume to provide both the detention time in table J.1 and to provide for the mass
load to be received by the unit. Figure 1: §217.249(2)(B)(i)
Table J.1 - Minimum Detention Times for Aerobic Digesters
Temperature (Degrees Celsius) Total Detention Time
15 60 days
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20 40 days
(ii) Multiple Stage. Multiple stage aerobic digestion consists of two or
more completely mixed reactors of the same volume operating in series. The residence time required for
this type of system to meet pathogen reduction goals may be 30% lower than the residence time
determined in (i) above.
(iii) Field Data. If an existing facility can demonstrate satisfactory
compliance with current fecal coliform levels for Class B sludge, that facility may continue to operate at
the time–temperature conditions at least as severe as those used during their tests. Significant increases
in flow, organic loading, or process modifications require new testing and verification of current time-
temperature operating parameters. Expansion of existing facilities may be designed and operated
according to time-temperature conditions previously established. New facilities may be re-rated after
sufficient supporting data is collected and evaluated.
(C) Design Requirements. The engineer shall consider providing an additional
tank to accommodate testing of the sludge prior to disposal. A maximum design concentration of two
percent solids concentration shall be used to calculate the total detention time for aerobic digesters which
concentrate the waste sludge only in the digester tank. A design concentration of up to three percent
solids may be used upon collection of supporting data. If additional thickening equipment, designed in
accordance with this chapter, is used, then the design concentration shall be reviewed on a case by case
basis. If used, diffuser shall be of the type which minimizes clogging, and the diffusers shall be designed
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to permit removal for inspection, maintenance, and replacement without dewatering the tanks. The
volatile solids loading shall be in the range of one to two tenths (0.1 to 0.2) pounds of volatile solids per
cubic foot per day, unless otherwise justified in the final engineering design report. Dissolved oxygen
concentration maintained in the liquid shall be 0.5 (½) milligrams per liter. Energy input requirements for
mixing shall be in the range of 0.5 to 1.5 horsepower per 1,000 cubic feet, where mechanical aerators are
utilized, and 20 to 30 standard cubic feet per minute per 1,000 cubic feet of aeration tank, where diffused
air mixing is utilized. Facilities shall be provided for effective separation and withdrawal, or decanting of
supernatant.
(2) Heat Stabilization.
(A) Capacity. The design of heat treatment systems shall be based on the
anticipated sludge flow rate (gpm) with the required heat input dependent on sludge characteristics and
concentration. The system shall be designed for continuous 24-hour operation to minimize additional heat
input to start up the system.
(B) Flexibility. Multiple units shall be provided unless nuisance-free storage or
alternate stabilization methods are available to avoid disruption to treatment works operation when units
are not in service. If a single system is provided, standby grinders, fuel pumps, air compressor (if ap
plicable), and dual sludge pumps shall be provided. A reasonable downtime for maintenance and repair
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based on data from comparable facilities shall be included in the design. Adequate storage for process
feed and downtime shall be provided.
(C) Equipment Features. The process shall provide heat stabilization in a
reaction vessel within a range from 175oC or 350 degrees Fahrenheit (350oF) for 40 minutes to 205oC or
400oF for 20 minutes at pressure ranges of 250 to 400 psig, or provide for pasteurization at temperatures
of 30oC or 85oF or more and gage pressures of more than one standard atmosphere (14.7 psi) for periods
exceeding twenty five (25) days. Sludge grinders shall be provided to protect the heat exchangers from
rag fouling. An acid wash or high pressure water wash system shall be available to remove scale from
heat exchangers and reactors. The decant tank shall be equipped with a sludge scraper mechanism and
shall be covered to prevent odor release. Corrosion resistant materials of construction shall be selected
for heat exchangers. Separate, additional grit removal (in addition to grit removal at the treatment works
influent) shall be considered to prevent abrasion of piping. Control parameters shall be adequately
monitored. Continuous temperature recorders shall be provided.
(D) Recycle Loads. The method of treatment for recycle streams from heat
treatment shall be detailed in the final engineering design report, and shall not impact water quality or the
facilities treatment processes negatively.
(6) Alkaline Stabilization.
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(A) Design Basis.
(i) Alkaline Dosage. The alkaline additive dosage required to stabilize
sludge is determined by the type of sludge, chemical composition of sludge, and the solids concentration.
Performance data taken from pilot plant test programs or from comparable facilities shall be used in
determining the proper dosage.
(ii) pH and Contact Time. The design objective shall be to furnish
uniform mixing in order to maintain the pH and contact time as specified in §§312.82-312.83 of this title
(relating to Pathogen Reduction and Vector Attraction Reduction) for alkaline addition in the alkaline
additive-sludge mixture.
(iii) Temperature and Contact Time. The design shall meet the
temperature and contact time objectives described in §§312.82-312.83(b) of this title for the alkaline-
sludge mixture.
(iv) Reliability. Multiple units shall be provided unless nuisance free
storage or alternate stabilization methods are available to avoid disruption to treatment works operations
when units are not in service. If a single system is provided, standby conveyance and mixers, backup
heat sources, and dual blowers shall be provided. A reasonable downtime for maintenance and repair
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based on data from comparable facilities shall be included in the design. Adequate storage for process,
feed, and downtime shall be included.
(B) Housing Facilities. Housing facilities shall be designed in accordance with
§217.247(5) of this title (relating to Chemical Pretreatment of Residuals). Mechanical or aeration
agitation which ensures uniform discharge from storage bins shall be provided.
(C) Feeding Equipment. Alkaline additive feeding equipment shall meet the
requirements of §217.247(6) of this title. Hydrated lime shall be fed as a 6 to 18 Percent Ca(OH2) slurry
by weight unless otherwise justified in the final engineering design report. Other suitable means shall be
developed for controlling the feed rate for dry additives, and the feed method shall be described in the
final engineering design report.
(D) Mixing Equipment. The additive/sludge blending or mixing vessel shall be
large enough to hold the mixture for 30 minutes at maximum feed rate. In a batch process, a pH greater
than 12 shall be maintained in the mixing tank during this period. In a continuous flow process, the nominal
detention time (defined as tank volume divided by volumetric input flow rate) shall be used in design, and
a pH greater than 12 shall be maintained in the exit line. Slurry mixtures may be mixed with either
diffused air or mechanical mixers. Mixing equipment shall be designed to keep the alkaline slurry mixture
in complete suspension.
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(i) Air Mixing. With air mixing using coarse bubble diffusers, a
minimum air supply of 20 scfm per 1000 cubic feet of tank volume shall be provided for adequate mixing.
The mixing tank shall be adequately ventilated and odor control equipment shall be provided.
(ii) Mechanical Mixing. Mechanical mixers shall be sized to provide 5 to
10 HP per 1,000 ft3 of tank volume. Impellers shall be designed to minimize fouling with debris in the
sludge.
(E) Detention Time. Pasteurization vessels shall be designed to provide for a
minimum retention period of thirty (30) minutes. Provisions for external heat shall be specified in the final
engineering design report.
§217.250. Sludge Dewatering.
This section contains the minimum design criteria to be used for comprehensive consideration of
sewage sludge dewatering unit processes. The engineer shall include in the final engineering design
report the rationale for the proposed units, design calculations, results from any pilot studies, all
assumptions, and appropriate references. The dewatering unit(s) shall be designed using mass balance
principles. Total suspended solids values are usually used to size dewatering units.
(1) General Requirements.
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(A) Centrate or Filtrate Recycle. Drainage from beds and centrate or filtrate
from dewatering units shall be returned to the head of the wastewater facility. The effects of these
organic loads shall be accounted for in the design of any downstream units.
(B) Sludge with Industrial Waste Contributions. Dewatering of municipal sludge
containing significant industrial waste, especially when thermal or chemical stabilization processes are
employed, shall not allow the release of constituents such as free metals, organic toxicants, or strong
reducing/oxidizing compounds in a manner which threatens water quality or discharge permit compliance.
(C) Redundancy. Where mechanical dewatering equipment is employed, at
least two units shall be provided unless adequate storage (separate or in-line) or an alternative means of
sludge handling is detailed in the final engineering design report. Whenever performance reliability and
sludge management options are soley dependent on production of dewatered sludge, each of the mechani
cal dewatering units provided shall be designed to operate for less than sixty (60) hours during any six day
period. In these cases, each facility shall be able to dewater in excess of 50% of the average daily sludge
flow with the largest unit out of service. The requirements for excess capacity shall depend upon the type
of equipment provided, peak sludge factor, and storage capability not otherwise considered.
(D) Storage Requirements. Where mechanical dewatering equipment will not
be operated on a continuous basis and the treatment works is without digesters with built-in short-term
storage, separate storage shall be provided. In-line storage of stabilized or un-stabilized sludge shall not
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interfere with the design function of any of the treatment unit operations. Separate sludge storage from
primary digesters shall be aerated and mixed as necessary to prevent nuisance odor conditions.
(E) Sampling Points. Sampling stations before and after each dewatering unit or
any appropriate segment of the unit shall be designed to allow the periodic evaluation of the dewatering
process.
(F) Bypass Requirements. All units shall have bypass capabilities to allow
maintenance to be performed on the units.
(2) Sludge Conditioning. Chemical or other additives shall be mixed with the sludge
quickly and completely. Adequate mixing time for the reaction between the chemical or other additive
shall be provided. Subsequent handling shall avoid floc shearing. The injection or addition point shall be
located in relation to downstream equipment and in relation to the combined effect of other additives.
Pilot plant testing or full size performance data shall be utilized to determine the characteristics and design
dosage of the additives and shall be determined in the final engineering design report. In-stream
flocculation/coagulation system designs shall be supported by comparable performance data or pilot plant
testing. If conditioning tanks are employed, mixers may be necessary, and the design shall include the
capability for variable detention times. Solution storage or day tanks may be smaller than the design
volume required for daily dosages, if the equipment design does not require continuous operation. A
minimum of eight (8) hours storage shall be provided unless the specific chemical or additive selected is
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adversely affected by storage. Storage for batch operations shall be adequate for one batch at maximum
chemical demand. Storage volume reductions shall be justified in the final engineering design report, and
other methods to ensure a continuous supply of chemicals through the operating day or batch shall be
provided.
(3) Sludge Drying Beds.
(A) Sizing. Drying beds size may be based on data from similar facilities in the
same geographical area with the same influent sludge characteristics. If such data is unavailable, or if the
executive director determines that the data is not appropriate for the proposed facility, sludge drying beds
shall be sized according to clauses (i) and (ii) of this subparagraph.
(i) Open Beds. The minimum surface area for sludge drying beds shall
be calculated using the values in Table J.2. These sizing factors are minimum sizing factors and do not
take into account additional surface area which may be needed to justify using sludge drying beds in areas
of the State that experience both high rainfall (greater than 45 inches per year on average) and high
relative humidity (yearly average of 50% or greater), as determined by utilizing data from the National
Weather Service. In these areas, other methods of sludge dewatering shall be utilized in lieu of sludge
drying beds. Other dewatering methods are not required if the design provides methods of effectively
dewatering sludge such as covering the beds; providing a means for accelerated dewatering; increasing
the size of the sludge drying beds sufficiently to store accumulated sludge during periods of extended high
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humidity and rainfall; and providing an alternative dewatering method to effectively dewater the sludge
during periods of extended high humidity and rainfall. The final engineering design report shall provide
justification for use of sludge drying beds in these high rainfall, high relative humidity areas of the state.
Figure 1: §217.250(3)(A((i)\
Table J.2 - Surface Area Requirements for Sludge Drying Beds
Stabilization Process Pounds Digested Dry Solids Per Square Foot Per Year
Anaerobic Digestion 20.0
Aerobic Digestion 15.0
(ii) Gravel Media Beds. These types of sludge drying beds shall be laid
in two or more layers. The gravel around the underdrains shall be properly graded and shall be at least 12
inches in depth, extending at least six inches above the top of the underdrains. The top layer shall be at
least three inches thick and shall consist of gravel 1/8 inch to 1/4 inch in size.
(iii) Sand Media Beds. These types of beds shall consist of at least 12
inches of sand with a uniformity coefficient of less than 4.0 and an effective grain size between 0.3 and
0.75 millimeters above the top of the underdrain.
(iv) Underdrains. Underdrains shall be at least four inches in diameter
and sloped not less than one percent to drain. Underdrains shall be spaced not more than 20 feet apart.
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(v) Decanting. A method of decanting supernatant may be installed on
the perimeter of the bed(s).
(vi) Walls. Interior walls shall be watertight and extend 12 to 24 inches
above and at least 6 inches below the bed surface. Exterior walls shall be watertight and extend 12 to 24
inches above the bed surface or ground elevation, whichever is higher. The exterior walls shall extend 12
to 15 inches below the bottom of the underdrain pipes.
(vii) Sludge Removal. Not less than two beds shall be provided, and the
beds shall be arranged to facilitate sludge removal. Concrete pads serving as vehicle support tracks shall
be provided for all percolation type sludge beds. Pairs of support tracks for percolation type beds shall be
on 20-foot centers.
(viii) Sludge Influent. The sludge pipe to the beds shall terminate at least
12 inches above the surface and be arranged so that the pipe will drain to a sump to be pumped to the
headworks. Concrete splash plates shall be provided at sludge discharge points.
(ix) Drying Bed Bottom. The bottom of the drying bed shall consist of a
minimum of one-foot layer of clayey subsoil having a permeability of less than 10-7 cm/sec. In locations
where the ground water table is within four (4) feet of the bottom, an impermeable concrete pad shall be
installed over the liner.
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(x) Bed Configuration. Bed width and configuration shall be determined
by a rational basis considering the sludge handling and treatment and sludge management options. If
polymers or other chemicals are used to enhance sludge dewatering, the effects of the polymer dosage on
uniform distribution of sludge on the bed shall be accounted for in the design.
(4) Modified Drying Beds. Vacuum assisted or other variations to the gravity drying bed
concept will be considered innovative and/or nonconforming technologies and shall be subject to
§217.10(2) (relating to Types of Approvals).
(5) Rotary Vacuum Filtration.
(A) Filtration Rate. The rates of filtering, in pounds of dry solids per square foot
of filter area per hour, for various types of sludge, in Table J.3, may be used for design with proper
conditioning. The actual value used shall be determined by the engineer and justified in the final
engineering design report. Figure 2: §217.250(5)(A)
Table J.3 - Filtration Rates
Type of Treatment Pounds of Dry Solids Per Square Foot Per Hour (Minimum
Maximum)
Primary 4-6
Primary and Trickling Filter 3-5
Primary and Activated Sludge 3-4
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(B) Duplicate Equipment. Unless dual trains are provided, the following
appurtenant equipment shall be provided in duplicate, with necessary connecting piping and electrical
controls, to allow equipment alternation: feed pump, vacuum pump and filtrate pump. Spare filter fabric
shall be provided except when metal coils are utilized.
(C) Filter Equipment. Wetted parts shall be constructed of corrosion-resistant
material. Drum and agitator assemblies shall be equipped with variable-speed drives, and provisions shall
be made for altering the liquid level.
(D) Filter Speed Requirements. The filter speed shall be variable.
(E) Pumps. Vacuum pumps shall be provided with a capacity of at least 1.5 cfm
per square foot for metal-covered drums. Vacuum receivers are required with dry-type vacuum pumps.
Filtrate pumps shall be of adequate capacity to pump the maximum amount of liquid to be removed from
the sludge. Each filter shall be fed by a separate feed pump to ensure a proper feed rate.
(6) Centrifugal Dewatering. Successful application of centrifugation of municipal type
sludge requires consideration of numerous factors. The bases of sizing and design shall be supplied in the
final engineering design report. Proper scale-up data pertaining to the particular sludge to be dewatered
shall be provided. The engineer shall account for the abrasiveness of each sludge supply in scroll
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selection. Adequate sludge storage shall be supplied for proper operation. Unless dual trains are provided,
the following spare appurtenant equipment shall be furnished with necessary connecting piping and
electrical controls to allow equipment alternation: drive motor, gear assembly, and feed pump. Each feed
pump shall be variable speed. Separate feed systems shall be equipped for each centrifuge. Centrifuges
shall be equipped with provisions for variation of scroll speed and pool depth. A crane or monorail shall
be furnished for equipment removal or maintenance. Provisions for adequate and efficient wash down of
the interior of the machine shall be an integral part of the design.
(7) Plate and Frame Presses.
(A) Sizing. When available, actual performance data developed from similar
operational characteristics shall be utilized for design and shall be detailed in the final engineering design
report. If no data is available, then the engineer shall submit the results of a pilot scale tests or full scale
tests as part of the final engineering design report. Appropriate scale-up factors shall be utilized for full
size designs if pilot scale testing is done in lieu of full-scale testing.
(B) Duplicate Equipment and Spare Parts. Unless multiple units are provided,
duplicate feed pumps, air compressors, and washwater booster pumps shall be provided. Additionally,
unless multiple units are installed, the following spare appurtenances shall be provided: at least one extra
plate for every ten required for startup, but not less than two; one complete filter fabric set; one closure
drive system; one feed pump; air compressor; and, one washwater booster pump.
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(C) Operational Requirements. Filter feed pumps shall be capable of a
combination of initial high flow low pressure filling, followed by sustained periods of operating at 100 to
225 psi. The engineer may use an integral pressure vessel to produce this initial high volume flow.
Operating pressures less than 225 psi may be used if actual performance data using similar sludge
justifying such a use is provided in the final engineering design report. The engineer may include
provisions for cake breaking to protect or enhance down line processes where necessary.
(D) Maintenance. Crane or monorail services capable of removing the plates
shall be provided. A high pressure water or acid wash system to clean the filter shall be provided.
(8) Belt Presses.
(A) Sizing. Actual performance data developed from similar operational
characteristics shall be utilized for design. A second belt filter press or an approved backup method of
sludge disposal shall be provided whenever a single belt press will be operated sixty (60) hours or more
within any consecutive five (5) day period, or whenever the average daily flow received at the treatment
works equals or exceeds four (4) mgd. Appropriate scale-up factors shall be utilized for full size designs
if pilot plant testing is performed in lieu of full-scale testing. The design basis for the belt filter press
dewatering system shall be detailed in the final engineering design report.
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(B) Duplicate Equipment and Spare Parts. Unless multiple units are provided,
duplicate feed pumps and washwater booster pumps shall be provided. Unless multiple units are installed,
the following spare appurtenances shall be provided: one complete set of belts, one set of bearings for
each type of press bearing; duplicate tensioning; and tracking sensors; one set of wash nozzles; one
doctor blade; and, duplicate conditioning or flocculation drive equipment.
(C) Conditioning. A polymer selection methodology, accounting for sludge
variability and anticipated sludge loading to the press, shall be described in the final engineering design
report.
(D) Sludge Feed. Sludge feed shall be as constant as possible to eliminate
difficulties in polymer addition and press operation. The range in feed variability shall be identified, and
equalization shall be provided as deemed necessary by the engineer. Inclusion of grinders ahead of the
flocculation system shall be evaluated by the engineer. A method for uniform sludge dispersion on the
belt shall be provided. Thickening of the feed sludge shall be an integral part of the design of the filter
press unless separate thickening or dual purpose thickening is fully detailed in the final engineering design
report.
(E) Filter Press Belts. The belt speed shall be variable. Belt tracking and
tensioning equipment shall be provided. Belt replacement availability shall be considered in the equipment
selection, especially if weave, material, width, or thickness may not be reasonably duplicated.
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(F) Filter Press Rollers. Rubber coating or other protective finish shall be
provided on the rollers. The maximum roller deflection and operating tension of the belt, shall be
considered in equipment selection. Roller bearings shall be watertight and be rated for a B-10 life of
100,000 hours.
(G) Water Supply Considerations. High pressure wash water shall be provided
for each belt and the specified operating pressure at the point of washwater discharge shall be
determined. Booster pumps shall be provided as deemed necessary by the engineer. Spray wash
systems shall be designed in a manner which allows them to be cleaned without interfering with the
system operation. Particular care in nozzle selections and optional nozzle cleaning systems shall be taken
when recycled wastewater is used for belt washing. Replaceable spray nozzles and spray curtains shall
be provided.
(H) Maintenance Requirements. Drip trays shall be provided under the press
and under the thickener, if gravity belt thickening is employed. Adequate clearance to the side and floor
shall be provided for maintenance and removal of the dewatered sludge. All electrical panels or other
materials which are subject to corrosion shall be located out of the area of the press. Doctor blade
clearance shall be adjustable.
§217.251. Sludge Storage.
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This section applies to the storage of residuals after processing and prior to final disposal or
removal from the site. Storage of solids on site may be provided in either liquid, dewatered, or dry form
where the solids have been stabilized in the treatment process.
(1) General. Storage facility shall be designed to abate nuisance and odor conditions.
All facilities shall be required to provide storage of waste sludge outside of the biological treatment
process. The design of all storage facilities shall take into account process design, sludge age, waste
stream concentration, operational hours, operational volume in tanks, decant or dewatering volumes and
characteristics, time frames needed for decanting or dewatering, and volume needed for storage and
sampling. Utilizing this information, a solids management plan shall be prepared by the engineer, and
detailed in the final engineering design report, which demonstrates a method of managing the waste solids
which will maintain the design sludge age for the biological process utilizing the sludge handling and
storage facilities.
(2) Solids Storage.
(A) Aerobically Digested Solids. Aerobically digested solids may be stored for
extended periods of time. The basin contents shall be kept thoroughly mixed using diffused air or
mechanical mixing. A minimum air requirement of 30 standard cubic feet per minute per 1000 cubic feet
of volume shall be provided. If mechanical surface aerators are used, a minimum horsepower
requirement of 1.0 horsepower per 1000 cubic feet of volume shall be provided. If earthen basins are
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used, they shall be lined in accordance with §217.202(3) and (4) of this title (relating to General Design
Considerations for Natural Systems).
(B) Anaerobically Digested Solids. Anaerobically digested solids may be stored
in covered basins or facultative solids basins. The anaerobically digested solids storage facility shall be
designed to abate nuisance and odor conditions. The facultative solids storage basin shall be designed to
maintain an aerobic surface layer free of scum accumulation. The organic loading rate for a facultative
solids storage basin shall not exceed 20 pounds of volatile solids per 1000 square feet of surface area per
day. Surface aerators shall be used to maintain the aerobic zone and breakup surface film. The surface
aerators shall be designed to minimize the mixing action between the aerobic and anaerobic zones. The
facultative solids basin shall have a minimum side water depth of 12 feet. The top 3 feet shall be kept
aerobic. If earthen basins are used, they shall be lined in accordance with §217.202 (3) and (4) of this
title.
(3) Dewatered Solids Storage. Dewatered solids with a solids content of less than 35
percent may be stored on site up to 7 days except for extenuating circumstances due to inclimate weather
that do not allow transport or disposal. Each occurrance shall be fully documented and kept on file. The
dewatered solids may be stored in steel or concrete containers and shall be located and stored to preclude
re-wetting by rainfall. Dewatered solids with a solids content of less than 50 percent and greater than or
equal to 35 percent, may be stored on site up to 90 days. The dewatered solids may be stored in
containers or in stockpiles. The storage facility shall be located to preclude re-wetting by rainfall. Solids
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stored in stockpiles shall be placed on an impervious pad to preclude groundwater contamination. Open
stockpiles shall include provisions for collecting rainfall runoff. All rainfall runoff shall be collected and
returned to the head of the treatment facility.
(4) Dried Solids Storage. Dewatered solids with a solids content of greater than or equal
to 50 percent may be stored on site in bins or covered facilities. Enclosed structures may produce
explosive gaseous byproducts or dust. The enclosed area of the storage structure shall be sufficiently
ventilated to eliminate the accumulation of dangerous gas mixtures. The enclosed storage structure shall
be mechanically ventilated with approximately 20 to 30 air changes per hour. All exhaust air shall pass
through an odor control system.
§217.252. Final Use or Disposal of Sludge.
The final use or disposal of sewage sludge shall be included in the design of the wastewater
treatment facility. The use, disposal, and transportation of sewage sludge shall be conducted in
accordance with the requirements contained in Chapter 312 of this title (relating to Sludge Use, Disposal
and Transportation).
(1) Quantities. Quantity of solids generated by the treatment process selected shall be
calculated or estimated from similar full scale facilities or pilot facilities. A mass balance approach shall
be used to determine the quantity of sludge produced at the facility.
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(2) Pollutants. Pollutants in sewage sludge shall be determined using standard method
laboratory test procedures. The use or disposal option shall be designed based on proper characterization
of the sewage sludge. Pollutant levels shall be less than the levels specified in Chapter 312 of this title.
(3) Pathogens. The wastewater treatment facility shall be designed to reduce pathogens
to levels specified in Chapter 312 of this title with regards to the ultimate use or disposal method.
(4) Vector Attraction. The wastewater treatment facility shall be designed to reduce
vector attraction of the sewage sludge to levels specified in Chapter 312 of this title with regards to the
ultimate use or disposal method.
(5) Emergency Provisions. The final engineering design report shall describe a backup
plan to be utilized to provide flexibility in the event of equipment failure or conditions which prevent the
primary use or disposal method.
(6) Weather Factors. The design shall account for weather factors such as rainfall, wind
conditions, and humidity in the selection of the use or disposal of sewage sludge.
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SUBCHAPTER K : DISINFECTION
§§217.270-217.278
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code as well as the authority to set standards to prevent the
discharge of waste that is injurious to the public health under §26.041 of the Texas Water Code.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.270. Applicability.
This subchapter details the requirements for disinfection, dechlorination, post aeration, and
sampling point locations.
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§217.271. Chlorine and Sulfur Dioxide Disinfection and Dechlorination Systems.
(a) Redundancy. All chlorine, sulfur dioxide disinfection, and dechlorination systems shall include
two banks of cylinders each. Each bank of cylinders shall include a sufficient number of cylinders to
meet the requirements of subsection (b)(2) of this section. The two banks of cylinders shall include an
automatic switch over device. This device shall automatically switch operations from an empty bank of
cylinders to a full bank of cylinders, in a manner which ensures that the chemical flow needed to assure
disinfection is continuously supplied. Sufficient space to store a bank of empty cylinders shall be
provided. A minimum of two chlorinators, sulfonators, or evaporators shall be provided. Chemical
delivery systems shall be setup so that the pound per day requirements in subsection (b)(1) of this section
may be met with the largest chlorinator, sulfonator, or evaporator out of service. Chemical delivery
systems shall also be provided with backup pumps for any injector water supply systems requiring booster
pumps.
(b) Capacity and Sizing.
(1) Pounds per Day Requirements. The pounds per day for which the chlorine and
sulfur dioxide gas withdrawal systems shall be sized shall be determined by using the 2-hour peak flow as
determined from §217.32(2) of this title (relating to Design of New Systems Organic - Loadings and
Flows) or §217.33(1) of this title (relating to Design Existing Systems - Organic Loadings and Flow) and
Equation 1.k. Table K.1 provides the minimum acceptable design chlorine dosage for disinfection. A
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demand of one unit of sulfur dioxide gas to dechlorinate at least one unit of chlorine gas shall be assumed
to determine the pounds per day of sulfur dioxide needed to neutralize the chlorine residual ($1 mg/l of
sulfur dioxide for every 1 mg/l of chlorine residual which shall be dechlorinated). Figure 1:
§217.271(b)(1)
PPD=Q*D*8.34 Equation 1.k
PPD = pounds per day of chlorine or sulfur dioxide required for
treatment
Q = peak 2 hour flow (millions of gallons per day)
D = chlorine concentration from Table 1, or sulfur dioxide dosage
needed to dechlorinate the expected chlorine residual
8.34 = conversion factor
Table K.1 - Minimum Design Chlorine Concentration Needed for Disinfection
Type of Effluent Chlorine Concentration (mg/l), (D)
Primary 15
Fixed Film 10
Activated Sludge 8
Tertiary Filtration Plant Effluent 6
Nitrified Effluent 6
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(2) Cylinder Bank Sizing. The number of chlorine or sulfur dioxide cylinders required,
per bank of cylinders, shall be determined as follows:
(A) Cylinder Withdrawal Rates.
(i) Gas Withdrawal. Determine the gas withdrawal rate per cylinder
using Equation 2.k and the variables from Table K.2. If the cylinders are not stored in a temperature
controlled area, the ambient temperature shall be based on the lowest 7-day average of the average daily
local temperatures over the last 10 years, as measured at the nearest National Oceanic and Atmospheric
Administration’s (NOAA) National Weather Service weather station. If storage of cylinders in non-
temperature controlled areas is proposed, refer to subsection(d)(2)(B) of this section. If heating blankets
are used with sulfur dioxide cylinders, refer to subsection (d)(1)(B) and (d)(2)(C) of this section.
HEATING BLANKETS ARE PROHIBITED ON CHLORINE GAS CYLINDERS. Figure 2:
§217.271(b)(2)(A)(i)
Wg=(TA-Tth)*F Equation 2.k
TA = Low Ambient Temperature, EF
Tth = Threshold Temperature, EF
F = Withdrawal Factor, lb/EF/day
W = Maximum Gas Withdrawal Rate per Cylinder, lb/dayg
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Table K.2 - Threshold Temperatures and Withdrawal Rates for Chlorine and Sulfur Dioxide - *
Gas and Cylinder Size Withdrawal Factor, (F)
lb/EF/day Threshold Temperature, (Tth) for Cylinder Mounted Vacuum Regulator, EF
Threshold Temperature, (Tth) for Manifold Systems at 10-15 psig Pressure, EF
150 pound Chlorine Cylinder
1.0 0 10
1 ton Chlorine Cylinder 8.0 0 10
150 pound Sulfur Dioxide Cylinder
0.75 30 40
1 ton Sulfur Dioxide Cylinder
6.0 30 40
* - Values found in the Handbook of Chlorination, Second Edition, Geo. Clifford White, Van Nostrand Reinhold
(ii) Liquid Withdrawal. If liquid withdrawal from one ton cylinders is
proposed, the following maximum withdrawal rates shall be used: Figure 3: §217.271(b)(2)(A)(ii)
Wl(Chlorine) = 9,600 pounds per day
Wl(Sulfur dioxide) = 7,200 pounds per day
(B) Cylinders per Bank. Calculate the number of cylinders per cylinder bank with
Equation 3.k: Figure 4: §217.271(b)(2)(B)
Cyl=PPD/Wg,l Equation 3.k
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Cyl = minimum number of cylinders required per bank (round
up to the nearest whole number)
PPD = pounds per day of chemical required as determined in
equation 1.K
Wg,l = pounds per day of chemical which may be withdrawn
per cylinder as determined in §§217.271(b)(2)(A)(I) or
(ii) of this title (relating to Gas Withdrawal and Liquid
Withdrawal).
(c) Dosage Control. Automatic dosage control shall be provided for all new and upgrades to
existing chlorine and sulfur dioxide systems. The dosage control shall be designed to automatically adjust
the dosage of chlorine or sulfur dioxide relative to at least the flow of the effluent stream.
(d) Handling of Chemicals. This subsection details requirements related to handling of sulfur
dioxide and chlorine system equipment and cylinders.
(1) Systems Utilizing 150 Pound Cylinders.
(A) Heated Rooms. Chlorine and sulfur dioxide systems which utilize 150 pound
cylinders shall be located completely indoors at a minimum temperature of 65EF. This provision applies to
all chemical feed equipment beginning at banks of cylinders and ending at the chlorinators or sulfonators,
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including the cylinders, chlorinators, and/or sulfonators. Unconnected cylinders may be stored outdoors,
provided the cylinders are moved indoors soon enough to allow them to reach at least 65EF before being
connected to the system.
(B) Heating Blankets for 150 Pound Cylinders. HEATING BLANKETS ARE
PROHIBITED ON CHLORINE GAS CYLINDERS. Heating blankets may be used on 150 pound
sulfur dioxide cylinders, in temperature controlled rooms, to increase the temperature inside the cylinders
above the ambient room temperature. If heating blankets are used for sulfur dioxide cylinders in
temperature controlled rooms, the engineer shall determine what temperature the heating blankets may
maintain inside the cylinders, when stored at a 65EF or greater room temperature. The temperature
which may be maintained inside the cylinder at the assumed room temperature is used as the ambient
temperature when determining the cylinder withdrawal rate in subsection (b)(2)(A) of this section. If
heating blankets are used the blankets shall include a mechanism which ensures that the blankets do not
heat the cylinders above 100EF. If heating blankets are used, a pressure reducing valve shall be installed
downstream of the operating cylinder(s) and the system shall be designed to deactivate blankets high
pressure is detected downstream to the cylinder(s).
(C) Separation. All chlorine equipment for systems utilizing 150 pound cylinders,
including the cylinders, shall be stored in rooms which are separate and completely isolated from any
sulfur dioxide equipment and sulfur dioxide cylinders. All sulfur dioxide equipment for systems which
utilize 150 pound cylinders, including the cylinders, shall be stored in rooms which are separate and
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completely isolated from any chlorine equipment and chlorine cylinders. The design of these systems shall
ensure that chlorine and sulfur dioxide will never come into contact with each other.
(2) Systems Utilizing One Ton Cylinders - Gas Withdrawal.
(A) Heated Rooms. Chlorinators and sulfonators for systems which utilize one
ton cylinders shall be located indoors at a minimum temperature of 65EF.
(B) Outdoor Storage of One Ton Cylinders. One ton chlorine and sulfur dioxide
cylinders may be stored outdoors for systems which utilize one ton cylinders. If one ton cylinders are
stored outdoors, the temperature used for system sizing needs to be determined. Subsection (b)(2)(A) of
this section provides details of how the proper temperature for system sizing may be obtained. If one ton
cylinders are stored outdoors, the design shall ensure that the cylinders are protected from direct sunlight.
Structures built to protect the cylinders from direct sunlight shall be constructed to allow safe removal and
replacement of the one ton cylinders. Additionally, operational cylinders stored outdoors, as deemed
necessary by the engineer, shall have heated piping to prevent gas reliquefication from occurring when
the chemical enters the heated building or when gas cools down in pressure pipe.
(C) Heating Blankets for One Ton Cylinders. HEATING BLANKETS ARE
PROHIBITED ON CHLORINE GAS CYLINDERS. Heating blankets may be used on one ton sulfur
dioxide cylinders to increase the operating temperature of the sulfur dioxide system. The engineer shall
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determine what temperature the heating blankets may maintain inside the cylinders based on the lowest 7
day moving average of the daily local temperatures over the last ten years. This temperature is used as
the ambient temperature when determining the cylinder withdrawal rate in subsection (b)(2)(A) of this
section. If heating blankets are used, the blankets shall include a mechanism which ensures that the
blankets will not heat the cylinders above 100EF. If heating blankets are used, a pressure reducing valve
shall be installed downstream from the operating cylinder(s), and the system shall have a high pressure
interlock to deactivate the blankets.
(D) Separation. For one ton cylinders, housing of the sulfur dioxide feed
equipment and cylinders shall be separate from the chlorination feed equipment and cylinders. For one
ton cylinders, the chlorination and sulfonation feed equipment shall be separated from the one ton chlorine
and sulfur dioxide cylinders with a gas tight wall. The following exceptions are allowed:
(i) Sulfur dioxide cylinders and chlorine cylinders may be stored in the
same area, provided: the cylinders are stored outdoors; a minimum distance of 10 feet is maintained
between the outlet valves of any one sulfur dioxide cylinder and the outlet valves of any one chlorine
cylinder; and provisions are made, such as markings or signs, to ensure that chlorine equipment and
chlorine storage containers cannot be confused with sulfur dioxide equipment and sulfur dioxide storage
containers.
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(ii) Sulfur dioxide and chlorine chemical feed equipment may be stored
in the same room provided that both systems are of the remote vacuum type, where no pressure gas
piping exists in the room, no cylinders are stored in the room, and the design ensures that chlorine and
sulfur dioxide will never be allowed to come into contact with each other.
(3) Systems Utilizing One Ton Cylinders - Liquid Withdrawal.
(A) Heated Rooms. Chlorinators and sulfonators shall be located indoors at a
minimum temperature of 65EF.
(B) Outdoor Storage of One Ton Cylinders. For systems utilizing liquid
withdrawal, the chlorine and sulfur dioxide cylinders may be stored outdoors without reducing the
withdrawal rates assumed in subsection (b)(2)(A)(II) of this section.
(C) Separation. The separation requirements for one ton cylinder liquid
withdrawal systems are the same as those for one ton cylinder gas withdrawal systems. Refer to
subsection (d)(2)(D) of this section for further details.
(e) Housing Requirements for Chlorine and Sulfur Dioxide Disinfection and Dechlorination
Systems. This subsection details the requirements for the building in which the chemicals are stored.
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(1) Floor Drains. Floor drains from chlorine or sulfur dioxide feed and storage rooms
shall not drain to any piping system common with other rooms of the wastewater treatment system. Floor
drains for chlorine rooms shall never drain to a piping system common with floor drains for sulfur dioxide
rooms.
(2) Doors and Windows. All doors shall open to the outside of the building, and doors
shall be equipped with panic hardware. All enclosed rooms shall include a minimum of one clear, gas-
tight window installed in the exterior door. Additional windows shall be installed, if deemed necessary by
the engineer, to ensure that the disinfection and dechlorination systems may be viewed without entering
the enclosed rooms.
(3) Ventilation. Forced mechanical ventilation, which provides a minimum of one air
change every three minutes, shall be included in all enclosed storage and feed rooms. The exhaust
equipment shall be automatically activated by external switches, and leak detection equipments. The fan
shall be located at the top of the room and shall push air across the room and through an exhaust vent on
the bottom of the opposite side. The location of the exhaust vent shall not allow contamination of air inlets
into other buildings. Negative pressure ventilation may be used in lieu of the forced mechanical
ventilation, provided the facilities have gas containment and treatment as prescribed by the current
Uniform Fire Code (UFC). Vents from any appurtenances or components of the sulfur dioxide or
chlorine gas feed systems shall be piped to a point which is not frequented by personnel, which is not near
a fresh air intake, and clearly identified.
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(4) Gas Detectors and Protection. Gas detectors and alarms shall be located in each
area containing chlorine or sulfur dioxide under pressure. Respiratory air-pac protection equipment, of the
pressure-demand type meeting the requirements of the National Institute for Occupational Safety and
Health (NIOSH), shall be available where pressurized gases are handled. Respiratory equipment shall be
stored in such a way that, upon discovery of a problem within the feed or storage room, the respirator
may be accessed in three minutes or less. The equipment shall not be located inside any rooms where
gases are stored or used under pressure. Instructions for using the equipment shall be kept with, or
posted next to, the equipment. The units shall use compressed air and shall have at least a 30-minute
capacity.
(f) Equipment and Materials. All equipment and materials used in the disinfection and
dechlorination systems shall be of the type that the manufacturer recommends for the pertinent chemical.
Some specific requirements for the equipment and materials are listed in paragraphs (1)-(6) if this
subsection.
(1) Storage Orientation. One ton cylinders shall be stored horizontally on trunnions, and
150 pound cylinders shall be stored vertically and be secured by a clamp or chain.
(2) Measurements. A scale for determining the amount of chemical used daily, as well
as the amount of chemical remaining in the container, shall be provided for all chlorine and sulfur dioxide
systems.
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(3) Pressure Piping Systems- Gas Transport. Gas transport pressure piping shall be
constructed of schedule 80 black seamless steel pipe with 2,000 pound forged steel fittings. THE USE OF
PVC AT ANY POINT IN THESE SYSTEMS IS PROHIBITED. For one ton cylinder systems, gas
filters shall be used upstream of any pressure reducing valves. Pressure reducing valves shall be installed
in pressure piping in the following situations: systems with long lengths of supply piping; sulfur dioxide
systems which utilize heating blankets; and, in the pressure piping on the gas discharge side of
evaporators. Rupture disks and high pressure switches which warn of disk rupture shall be installed in
pressure piping at the gas discharge side of any evaporators. A heated leg drop sediment trap shall be
provided where the gas line enters a chlorinator or sulfonator. Sulfur dioxide systems shall have 316
stainless steel seat and stem in lieu of the monel seat and stem used in chlorine systems.
(4) Pressure Piping Systems - Liquid Transport. THE USE OF PVC AT ANY POINT
IN THESE SYSTEMS IS PROHIBITED. Manifolding ton containers for simultaneous liquid chemical
withdrawal is prohibited. Liquid piping systems shall include a rupture disk, a pressure switch to warn of
disk rupture and an expansion chamber.
(5) Vacuum piping. Vacuum piping and fittings may be PVC or 316 stainless steel
downstream of the vacuum regulator, using socket joints, not threaded.
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(6) Diffusers. The engineer shall include calculations in the engineering report which
verify that a minimum velocity of 10 feet per second exists through any chlorine or sulfur dioxide system
diffusers or a mechanical mixer shall be provided.
§217.272. Design of Sodium Hypochlorite and Sodium Bisulfite Systems.
(a) Redundancy. All sodium hypochlorite and sodium bisulfite systems shall include a minimum
of two chemical solution pumps. Sufficient pumps shall be included in the design to ensure that the
capacity requirements of §217.271(b)(1) of this title (relating to ) may be met with the largest pump out
of service. The pumping system shall be set up in a manner which ensures that permit compliance is
maintained in the event of a pump failure.
(b) Capacity and Sizing. The gallons per hour, for which each chemical liquid solution pumping
and piping network needs to be sized, shall be determined as follows:
(1) Sodium Hypochlorite (NaOCl).
(A) Determine Pounds Per Day of Chlorine Required. Refer to table 1 and
equation 1 in §217.271(b)(1) of this title (relating to Chlorine and Sulfur Dioxide Disinfection and
Dechlorination Systems) to determine the pounds per day of chlorine required.
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(B) Cl2 Determination. Determine pounds of available Cl2 per gallon of NaOCl
solution using values supplied by chemical manufacturer and appropriate references.
(C) Gallons per Hour Determination. Calculate the Gallons per Hour for which
the chemical metering equipment shall be sized using the values found in §217.271(b)(1) of this title in
Equation 4.k. Figure 1: §217.272(b)(1)(C)
R=PPD/(24*C) Equation 4.k
R = minimum size of chemical metering equipment, (gal/hr)
PPD = pound per day of Cl2 which shall be delivered to the wastewater,
(ln/day)
C = Pounds of available Cl2 in one gallon of NaOCl, (lb Cl2/gal)
(2) Sodium Bisulfite (NaHSO3).
(A) Determine Assumed Pounds Per Day of Chlorine Residual Which Shall be
Dechlorinated. Use equation 1 in §217.271(b)(1) of this title (relating to Pounds Per Day Requirements)
to determine the pounds per day of chemical required.
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(B) Calculate Pounds of NaHSO3 Needed. The minimum amount of NaHSO3
needed to dechlorinate one pound of chlorine is 1.465 pounds. Multiply the pounds per day of chlorine
which shall be dechlorinated, as determined in subparagraph (A) of this paragraph, by 1.465 pounds of
NaHSO3 per pound of Cl2, to determine the pounds of NaHSO3 needed.
(C) Calculate the Gallons per Hour (R) of NaHSO3 solution which shall be
delivered by the chemical metering equipment with equation 5.k. Figure 1: §217.272(b)(2)(C)
R=(lbs NaHSO3)/[(10.9 lbs NaHSO3/gallon NaHSO3)*(1/solution strength in percent)*24]
Equation 5.k
(c) Dosage Control. Automatic dosage control shall be provided for all upgrades to existing
sodium hypochlorite and sodium bisulfite systems, and for all new sodium hypochlorite and sodium bisulfite
systems. Dosage control systems shall be designed to automatically adjust sodium hypochlorite or sodium
bisulfite feed rate to correspond to at least the flow of the effluent stream.
(d) Handling of Chemicals.
(1) Storage Tank Sizing. For solution strengths greater than or equal to 10%, bulk
storage facilities shall not be sized to store more than a 15-day supply of sodium hypochlorite unless
automatic feed control is supplied by residual analyzer or oxidation-reduction potential (ORP) monitoring
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to compensate for solution degradation. In cases where sodium hypochlorite solution strengths are less
than 10%, and where residual analyzers or ORP instruments are provided for sodium hypochlorite
solutions, the facilities shall not be sized to store more than a 30-day supply of chemical. A minimum of
two tanks shall be provided for facilities with design flows above 1 mgd.
(2) Temperature considerations. If sodium hypochlorite tanks are not stored indoors, the
tanks shall be opaque, or otherwise block sunlight penetration. Sodium bisulfite storage and piping
facilities which are to be stored outdoors shall be insulated and heat traced in locations where the ambient
temperature, based on the lowest 7-day average of the average daily local temperatures over the last 10
years as measured at the nearest National Oceanic and Atmospheric Administration’s (NOAA) National
Weather Service weather station, is below 40EF.
(e) Equipment and Materials. Materials used for storage, pumping, and transport of sodium
hypochlorite shall be per manufacturer’s recommendation and suitable for use with an extremely
corrosive strong oxidant chemical environment. Materials used for storage, pumping and transport of
sodium bisulfite shall be per manufacturer’s recommendations and suitable for use with an acidic, strong
reducing agent chemical environment.
(f) Safety.
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(1) Ventilation. Chemical storage areas shall be ventilated sufficiently to prevent buildup
of fumes.
(2) Liquid-depth indicators. External-tank liquid-depth indicators shall be provided to
discourage routine opening of tank lids.
(3) Spill containment. Chemical storage areas shall be provided with secondary
containment equal to 125 percent of the volume of the full content of the largest storage tank. Manifolded
tanks shall be provided with secondary containment adequate to contain 125 percent of the cumulative
manifolded tank volume, unless the system piping design precludes a combined release. Tanks shall be
placed on equipment pads elevated above the secondary containment maximum liquid level, or provided
with positive drainage from below the tank. Containment for sodium hypochlorite shall be separate from
containment for sodium bisulfite.
(4) Emergency and Protective Equipment. Chemical storage areas shall be provided
with at least one emergency eye wash station and adequate personal protective equipment for all plant
personnel working in the area.
§217.273. Application of Disinfection and Dechlorination Chemicals.
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(a) Mixing Requirements. New facilities shall be constructed so that the applied chlorine is
thoroughly mixed with the wastewater prior to entry into the chlorine contact chamber. Any mixing zones,
which exist within the chlorine contact basins of existing facilities, shall not be counted as part of the
volume needed for disinfection.
(1) Chlorine and Sodium Hypochlorite. Effective initial mixing may be provided by
applying the chlorine gas or solution in a highly turbulent flow regime created by in-line diffusers,
mechanical mixers, or jet mixers. The mean velocity gradient in the area of turbulent flow, (G value),
shall exceed 500/sec.
(2) Sulfur Dioxide and Sodium Bisulfite. The appropriate degree of mixing for sulfur
dioxide and sodium bisulfite systems shall be determined by the engineer, but shall be sufficient to comply
with all relevant discharge permit requirements. As deemed necessary by the engineer, a mean velocity
gradient, or G value, of 250/secor greater shall be provided.
(b) Disinfection Contact Basins. Chlorine contact basin shall be designed to provide a minimum
hydraulic residence time at 2-hour peak flow of 20 minutes. Contact chambers shall be designed to
prevent short circuiting, and shall assure that at least 70 percent of the wastewater is retained in the basin
for 20 minutes. The final engineering design report shall include supporting data from contact basin
design models, performance data of similar designs, or field tracer studies.
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(c) Dechlorination Contact Time. Sufficient mixing and contact time between the disinfected
wastewater and the dechlorinating agent shall be provided to ensure continuous compliance with the
permitted chlorine limits. A minimum contact time of 20 seconds shall be provided at peak flow.
§217.274. Other Chemical Disinfection and Dechlorination Systems.
All chemical disinfection or dechlorination systems which are not discussed in this subchapter,
such as chlorine dioxide, ozone, all tablet or powder disinfection and dechlorination systems, and liquid
solution disinfection and dechlorination systems other than sodium hypochlorite and sodium bisulfite, shall
be subject to the requirements of §217.10(2) of this title (relating to Types of Approvals).
§217.275. Ultraviolet Light Disinfection Systems.
Refer to §309.3 of this title (relating to Application of Effluent Sets) for details of the permit
requirements which exist when Ultraviolet (UV) light disinfection systems are used.
(1) Definition.
(A) Modules. A module is defined as a grouping of UV lamps, electrically and
physically connected together to form an independent subcomponent of a bank and is not capable of
treating the full chanel design width and depth.
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(B) Banks. A bank is defined as a grouping of individual UV lamps or modules,
electrically connected together and physically connected together or physically adjacent to each other that
forms a complete unit capable of treating the full channel design width and depth. A bank may be
composed of several indiividual lamps or severl modules. A complete UV system may be composed of
multiple channels with several banks in each channel.
(2) Redundancy. Ultraviolet (UV) disinfection systems shall include a minimum of two banks of
UV bulbs. UV light disinfection systems shall be designed so that the dosage requirements determined
from paragraph (4) of this section may be met assuming the largest bank of UV bulbs in each channel out
of service at 2-hour peak flow as defined in §217.32(1) or §217.33(1) of this title (relating to Design of
New Systems - Organic Loadings and Flows and Design of Existing Systems - Organic Loadings and
Flows).
(3) Monitoring and Alarms. The following items shall be continuously monitored: flow
rate in the UV disinfection channel(s), UV transmittance, liquid level in the UV disinfection channels,
status of each UV bank (On/Off), status of each UV lamp (On/Off), UV intensity measured by the
greataer of one probe per bank or one probe per 40 lamps, and lamp age in hours of each UV lamp.
Flowrate alone shall not be relied upon as a means for automatic control (flow pacing). Any automatic
system must account for flowrate, intensity of the lamps, and the age of the lamps continually. Each bank
of UV lamps shall be capable of indicating elapsed operating time. An alarm system shall be incorporated
as part of the design for all UV systems. Plants which are unattended at any time shall include telemetry
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as part of their alarm system. The telemetry system shall notify an experienced operator in the event of a
major UV alarm. A UV control system shall include the following minimum alarm conditions:
(A) Minor alarms indicate the need for operator attention as soon as possible.
Minor alarms shall be included for low UV intensity (45% after 100 hours burn in), high temperature and
individual lamp failure.
(B) Major alarms indicate the need for immediate operator attention. Major
alarms shall be included for low UV intensity (25% after 100 hour burn in), adjacent lamp failure, multiple
lamp failures (more than 5% of lamps in one bank), communication failure and module failure.
(3) Hydraulics. Manufacturer’s of UV systems shall provide tracer studies for each
lamp/ballast configuration of their UV systems. These tracer studies shall determine a residence time
distribution (RTD) for each configuration of lamps/ballasts. These RTDs shall be used in conjunction with
a bioassay (as described in subsection (d) of this section) as the basis of design.
(4) Dosage and System Sizing. Low pressure systems may be sized based on the latest
version of the EPA’s UV disinfection model titled UVDIS. The executive director may require a bioassay
to be performed on low pressure systems sized using the UVDIS model. The sizing of all other UV
disinfection systems shall be based on the results of a bioassay which was performed on a system
developed by the same manufacturer as the manufacturer of the proposed system and on the same
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lamp/ballast configuration as the configuration for the proposed UV system. The results of the bioassay
shall be used to determine the minimum dose of the UV system and the minimum number of
lamps/ballasts per unit of flow rate. If the proposed design accommodates different lamp/ballast
configurations, comparable bioassays shall be provided. Bioassays will only be considered comparable if
each follows the same testing protocol under similar test conditions. The bioassay procedure shall
generally conform to the publication, USEPA (1986) “Design Manual: Municipal Wastewater
Disinfection,” EPA/625/1-86/021. The UV system shall be designed to deliver a minimum specified dose
based upon all of the following: UV lamp output at 65% of nominal, UV transmittance based on treatment
process, RTDs, and the results of a bioassay. In lieu of the bioassay, the UV system may also be sized
based on full scale pilot test data. The testing results and protocol shall be clearly detailed in the final
engineering design report. Systems sized on full scale pilot test data will be considered nonconforming
technology for the purposes of this rule and shall be subject to the requirements of §217.10(2) of this title
(relating to Types of Approvals).
(5) Reactor Design. The unobstructed approach channel shall have a minimum length
before the first UV bank of 4 feet, or 2 times the channel water depth, whichever is larger. The
unobstructed downstream channel length following the last bank of UV lamps, before the fluid level
control device, shall have a minimum length of 4 feet, or 2 times the channel water depth, whichever is
larger. All inlets to UV reactors shall be designed to hydraulically distribute the reactor influent in plug
flow with radial dispersion. Inlet channels shall provide equal flow distribution across all UV channels.
The downstream discharge point of the reactor shall include level controls which ensure that the UV bulbs
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remain submerged at a near constant depth regardless of flow. The maximum water surface elevation
variation in each UV channel is 3 inches between periods of no flow (zero flow) and the maximum design
peak flow. The upstream and downstream portions of the UV reactor channel between UV banks shall
be covered sufficiently to shut out all natural light (light tight).
(6) Cleaning and Maintenance. Provisions for routine cleaning of the UV bulbs and
modules shall be incorporated into the design. Also, the design shall include provisions for draining each
UV disinfection channel. Spare parts shall be provided for all UV systems. At a minimum, spare parts
provided shall meet the greater of one complete uninstalled module, or, as a percentage of the total
system, 5% lamps, 2% ballasts, 5% enclosure tubes, and 2% modules (minimum of one unit).
(7) Safety. Appropriate clothing, UV rated face shields, and safety glasses or goggles
shall be worn in the reactor area.
§217.276. Power Reliability.
All disinfection systems shall include backup power provisions which are capable of providing
sufficient power to operate all power dependant components of the disinfection system during any power
outage. The backup power shall automatically restart the disinfection system during a power outage.
Details describing backup power requirements for various wastewater treatment components are found in
§217.35 of this title (relating to Backup Power Requirements).
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§217.277. Post Aeration.
Post aeration shall be provided as needed to ensure permit complied with dissolved oxygen (DO)
requirements. If the permit requires a minimum DO of 5 mg/l or greater, the engineer shall include details
in the final engineering design report which explain how the minimum DO level will be maintained.
§217.278. Sampling Points.
Sampling points which may be safely accessed by the wastewater treatment system operators
shall be provided at all wastewater treatment systems. Sufficient sampling points shall be provided to
allow all permit requirements to be monitored safely on a routine basis. Any units which are downstream
of the final monitoring location shall not be considered part of the treatment train for purposes of
determining whether or not the wastewater treatment system will treat wastewater sufficiently to ensure
continuous permit compliance.
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SUBCHAPTER L : SAFETY
§§217.290-217.307
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. These rules are also proposed under the Texas Water Quality
Control Act, which gives the commission the authority to adopt rules for the approval of disposal system
plans under §26.034 of the Texas Water Code. These rules are also proposed under §26.041 of the
Texas Water Code, which gives the commission the authority to use any means to prevent a discharge of
waste that is injurious to public health.
There are no other rules, codes, or statutes that will be affected by this proposal.
§217.290. Applicability.
This subchapter details the general safety requirements which shall be followed in the design,
construction, and installation of wastewater treatment facilities.
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§217.291. General Policy.
The engineer shall consider occupational safety, health hazards and risks to the workers, other
persons, and the public as part of treatment process, disinfection, and chemical selection in preliminary
and final designs. The engineer shall consider selecting and specifying processes that require or use non
hazardous, non-toxic, less hazardous or less toxic chemicals, diluted forms of chemicals, and a minimum
inventory of chemicals. In addition to requirements set forth in this subchapter, the engineer shall
consider guidelines established under 29 CFR Parts 1901.1 (OSHA) and other regulatory authorities.
Specific attention shall be paid to the following topics: walking and working surfaces; means of access
and egress; occupational health and environmental controls; hazardous materials and toxic and hazardous
substances; general environmental control; fire and explosion hazard protection; compressed gas and
equipment; material handling and storage; machinery and machine guarding; hand and power tools and
other hand held equipment; electrical systems; confined space entry; lockout/tagged of energy sources;
site fence and other fencing; portable equipment such as lighting, blowers, and ventilators; warning signs
for slippery areas; non-potable water; low head clearance; open service manholes, vaults, and tanks;
railways and walkways; hazardous/toxic chemical storage areas; ventilation; and eyewash fountains and
safety showers. For the purposes of this rule, compliance with these requirements shall be shown by
implementation of §§217.292 and 217.293 of this title (relating to Safety Audit and Job Hazard Analysis
and Protective Equipment Lists).
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§217.292. Safety Audit.
For existing facilities being modified or expanded, the owner or designated representative and to
the extent that documentation is available, shall conduct a safety audit of the facility for the prior three-
year period in order to determine the locations, causes, types of injuries, and jobs being performed when
the injuries occurred. Locations and jobs associated with high injury or incident rates shall be evaluated,
corrective action identified, and corrective measures implemented that will eliminate the cause or reduce
the frequency, magnitude, and duration of exposure to the cause of the injury. Corrective actions
identified, that may be eliminated or minimized as part of the modification or expansion project, shall be
addressed in the design of the facilities.
§217.293. Job Hazard Analysis and Protective Equipment Lists.
For new, expanded, or modified facilities, an analysis of hazardous operation and maintenance
tasks shall be performed by the owner or designated representative. The intent is to develop layouts that
will result in the easiest, safest, and cost-effective way to accomplish potentially hazardous tasks. Based
on the hazardous jobs workers shall perform, and in conjunction with the owner or designated
representative, the engineer shall develop a list of the following: tools, equipment, and supplies; fixed and
portable lifting equipment; fixed and portable monitoring equipment; personal protective equipment and
clothes; warning signs and guards; and first-aid supplies. The tools shall be sufficient to allow workers to
safely and properly operate equipment; perform required preventive maintenance, as per manufacturers'
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minimum requirements; make repairs; and otherwise maintain processes, pumps, motors, blowers,
compressors, laboratory, instrumentation, and other equipment.
§217.294. Railings, Ladders, Walkways, and Stairways.
Openings in railings shall have removable chains. Open valve boxes, pits, tanks, and basins
extending less than four feet above ground shall be guarded by railings. Steep and vertical ladders are
acceptable for infrequent access to equipment. Walkways, steps, landings, and ladder rungs shall have a
non-slip finish. Walkways above open tanks shall have kick plates. Ladders shall have flat safety tread
rungs and extensions at least one (1) foot out of a vault. Seven feet of clearance shall be provided for
overhead piping unless piping is padded to prevent head injury and warning signs are provided.
§217.295. Electrical Code.
Electrical design shall conform to local electrical codes. Where there are no local electrical
codes, the design shall conform to the National Electrical Code. Adequate lighting shall be provided,
especially in areas to be serviced by personnel on duty during hours of darkness.
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§217.296. Unsafe Water.
When non-potable water is made available to any part of the plant, all yard hydrants and outlets
shall be properly marked "Unsafe Water," and all underground and exposed piping shall be identified as
specified in §217.298 of this title (relating to Color Coding of Piping).
§217.297. Plant Protection.
The plant area shall be completely fenced and have lockable gates at all access points. Plants
containing open clarifiers, aeration basins, and other open tanks shall be surrounded by an eight-foot fence
with a minimum single apron barbed wire outrigger, or a six-foot high fence with three strands of barbed
wire to a height of 78 inches. A five strand barbed wire fence may be used in lieu of these chain link or
board fences in rural areas for stabilization ponds, lagoons and overland flow plots. Hazard signs stating
"Danger - Open Tanks - No Trespassing" shall be secured to all wastewater treatment system fences,
within visible sighting of each other, as well as on all gates and levees. Plants shall have at least one all-
weather access road with the driving surface situated above the 100-yr. flood plain or shall detail an
alternate means of access during 100-year flood conditions in the final engineering design report.
§217.298. Color Coding of Piping.
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All piping for new facilities shall be color coded. All non-metallic underground plant piping for
new facilities shall be installed with tracer tape. All piping, for upgrades or modifications to facilities, both
exposed and to be buried or located out of view, which will contain gas, chlorine, or other hazardous
materials, shall be color coded and installed with tracer tape. Non-potable waterlines shall also be iden
tified with a proper color coding. These lines shall be painted white and be stenciled "NON-POTABLE
WATER" or "UNSAFE WATER," or, if the lines are to be used as part of a reclaimed water system in
accordance with Chapter 210 of this title (relating to the Use of Reclaimed Water), these reclaimed water
lines shall be marked and installed in accordance with the requirements of Chapter 210 of this title. The
following coding is required:
(1) Sludge Line - Brown;
(2) Gas Line - Red;
(3) Potable Water Line - Blue;
(4) Chlorine Line - Yellow;
(5) Sulfur Dioxide - Lime Green with Yellow Bands;
(6) Sewage Line - Grey;
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(7) Compressed Air Line - Green;
(8) Heating Water Line - Blue with 6" red bands spaced 30" apart;
(9) Power Conduit - Orange; and
(10) Reclaimed Water Lines - Purple.
§217.299. Portable Ventilators and Gas Detection Equipment.
Portable, gasoline-operated ventilators shall be provided for ventilating manholes. Personal gas
detectors are required for wear by all personnel whose jobs require entering enclosed spaces capable of
having accumulations of hydrogen sulfide or other harmful gases. An approved, personnel-retrieval
system shall be provided for confined space entry.
§217.300. Potable Water.
Ppotable water should be provided to the plant site. If potable water is provided, double check
backflow preventers shall be provided at the main plant service. Atmospheric vacuum breakers are re
quired at all potable water wash down hoses.
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§217.301. Freeze Protection.
All surfaces subject to freezing shall be adequately sloped to prevent standing water.
§217.302. Noise Levels.
Noise levels in all working areas shall be kept below standards established by the Occupational
Safety and Health Act. REMOVABLE NOISE ATTENUATORS should not be utilzed.
§217.303. Safety Training.
Safety training shall be provided annually to all employees.
§217.304. Confined Space.
The engineer should avoid designing or otherwise providing areas that may be considered
confined spaces as described in 29 CFR 1910.146.
§217.305. Plans and Specification Safety Review.
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The design plans and specifications should include reasonable and adequate safeguards to
minimize worker exposure to workplace hazards. To the extent reasonably and economically possible,
environmental conditions that increase the probability of worker accidents during normal operations and
emergency situations shall be minimized. Hazards to be considered include abnormal atmospheres;
airborne hazards; burns; harmful chemicals; confined spaces; drowning; earthquakes; electrical shock;
elevated areas; explosive gases, liquids, and dusts; falls; fires; flooding; food contamination; housekeeping;
impact; infections and diseases; ingress and egress; laboratory; ladders, stairs, and ramps; lifting; materials
handling; moving machinery; natural hazards; night operations and maintenance; noise; noxious gases and
vapors; openings; open tanks; overhead fixtures, pipes, and conduits; pinning and crushing; radioactive
material; slips and falls; spillage and sprays; storms; vapors and dust; vehicles; ventilation; vibration;
walkways; weather, and yard work. Environmental conditions that shall be considered include noise,
humidity, odor, temperature, illumination, vibration, and chemical exposure.
§217.307. Other Safety Design Guidelines.
For additional safety design guidelines, the engineer shall refer to latest edition of Design of
Municipal Treatment Plants, WEF Manual of Practice No.8, published by the Water Environment
Federation, 601 Wythe Street, Alexandria, Virginia 22314-1994, or other publications or authoritative
documents.
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The Texas Natural Resource Conservation Commission (commission) proposes the repeal of
§§317.1-317.15, concerning the design criteria for sewerage systems.
EXPLANATION OF PROPOSED RULE
Chapter 317 is being substantially revised to bring the standards and requirement of design criteria for
wastewater treatment facilities up to date with current engineering practices and technology. The
revision also provides opportunities for variances for innovative technology and non-conforming
technology that may be rare today, but commonplace in the next few years.
The extensive rewrite of the chapter, plus the commission’s goal of having all of the water-related rules
and regulations contained in the 200 series, make it reasonable to repeal Chapter 317 and propose,
through another action, a new Chapter 217 concerning the design criteria for sewerage systems.
An industry workgroup made up consulting engineers, wastewater treatment system operators, equipment
manufacturers and suppliers, and affected municipalities’ representatives has assisted commission staff in
recommending the repeal of this chapter and has assisted staff in developing the new proposed
requirements found in proposed Chapter 217.
FISCAL NOTE
Stephen Minick, Strategic Planning and Appropriations Division, has determined that for the first five-year
period the proposed repeal is in effect, there will be no significant fiscal implications for the state or local
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governments. The repeal of this chapter and the proposed new chapter may provide a cost savings for
local governments from better guidance on acceptable sewage system designs and clearer flexibility for
innovative technology.
PUBLIC BENEFIT
Mr. Minick has also determined that for the first five years that the proposed repeal is in effect, and the
proposed new chapter is in effect, the public benefit anticipated will be wastewater design criteria that is
clearer and more consistent with current engineering practices and that should lead to better designed and
more efficiently functioning wastewater treatment facilities. There are no significant fiscal implications
anticipated for small businesses. There are no economic costs anticipated for any person subject to the
repeal as proposed.
DRAFT REGULATORY IMPACT ANALYSIS
The commission has reviewed the proposed rulemaking in light of the regulatory analysis requirement of
Texas Government Code, §2001.0225, and has determined that the rulemaking is not subject to
§2001.0225 because it does not meet the definition of a major environmental rule as defined in the act,
and it does not meet any of the four applicability requirements listed in §2001.0225(a).
TAKINGS IMPACT ASSESSMENT
The commission has prepared a Takings Impact Assessment for these rules pursuant to Texas
Government Code Annotated, §2007.043. The following is a summary of that assessment. The specific
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purpose of the proposed repeal is to remove the current and outdated Chapter 317 rules and to propose
new and updated criteria under a new Chapter 217. The proposed repeal of these rules will not affect
private real property which is the subject of the rules.
PUBLIC HEARING
A public hearing on the proposal will be held ________________at ___________ a.m. in Room _____
of the commission Building __, located at 12100 Park 35 Circle, Austin. The hearing is structured to
receive oral or written comments by interested persons. Individuals may present oral statements, when
called upon, in the order of registration. Open discussion will not occur during the hearing; however, a
commission staff member will be available to discuss the proposal 30 minutes prior to the hearing and will
answer questions before and after the hearing.
SUBMITTAL OF COMMENTS
Written comments on the proposal should refer to Rule Log No. 95100-317-WT and may be submitted to
Betty Bell, Texas Natural Resource Conservation Commission, Office of Environment Policy, Analysis
and Assessment, MC 205, P.O. Box 13087, Austin, Texas 78711-3087, (512) 239-6087. Comments may
be faxed to (512) 239-5687, but must be followed up with the submission and receipt of the written
comments within three working days of when they were faxed. Written comments must be received by
5:00 p.m., ______________. For further information concerning this proposal, please contact Louis C.
Herrin, III, P.E., Texas Natural Resource Conservation Commission, Water Permits and Resource
Management Division, (512) 239-4552.
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COASTAL MANAGEMENT PLAN
The executive director has reviewed the proposed repeal and found that the rule is neither identified in
Coastal Coordination Act Implementation Rules, 31 TAC §505.11, relating to Actions and Rules Subject
to the Coastal Management Program, nor will the proposed repeal affect any actions/authorization
identified in Coastal Coordination Act Implementation Rules, 31 TAC §505.11. Therefore, the proposed
rule is not subject to the CMP.
STATUTORY AUTHORITY
These rules are proposed under the Texas Water Code, §5.102, which provides the commission with the
authority to carry out duties and general powers of the commission under its jurisdictional authority as
provided by Texas Water Code, §5.103. The proposed repeal and proposal of new rules are also
proposed under the Texas Water Quality Control Act, which gives the commission the authority to adopt
rules for the approval of disposal system plans under §26.034 of the Texas Water Code.
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CHAPTER 317
DESIGN CRITERIA FOR SEWERAGE SYSTEMS
§317.1. General Provisions.
§317.2. Sewage Collection System.
§317.3. Lift Stations.
§317.4. Wastewater Treatment Facilities.
§317.5. Sludge Processing.
§317.6. Disinfection.
§317.7. Safety.
§317.8. Design and Operation Features.
§317.9. Appendix A.
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§317.10. Appendix B - Overland flow process.
§317.11. Appendix C - Hyacinth Basins.
§317.12. Appendix D.
§317.13. Appendix E - Separation Distances.
§317.15. Appendix G - General Guidelines for the Design of Constructed Wetlands Units for
use in Municipal Wastewater Treatment