Contractor Awareness Training Below Ground Facilities 2016

A Fairfax County, VA, publication

Department of Public Works and Environmental Services

Working for You!

Stormwater Maintenance Awareness TrainingFor privately maintained stormwater management facilities

Maintenance and Stormwater Management Division (MSMD)

Spring 2016

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Stormwater Maintenance Awareness Training

MSMD/DPWES

Course ScheduleAM session (includes two short breaks)

– History of SWM and regulations– County inspection basics– The inspection report and MAR– Common SWM/BMP types

• Common maintenance issues-General

– Common SWM/BMP types, deficiencies, and remedies• Above Ground Facilities

12:00-1:00 PM Lunch

PM session (includes two short breaks)– Common SWM/BMP types, deficiencies, and remedies

• Below Ground Facilities• Vegetative Practices

– Closing remarks/questionsNOTE: All pictures, unless noted, are the property of Fairfax County.

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Below Ground Facilities-General Safety

The County’s private inspection program does NOT allow for Confined Space Entry!

Please ensure you are properly certified, have the proper entry permits, and are appropriately equipped before entering any

applicable confined space!

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Below Ground Facilities-Underground Detention (UG)

• An underground basin which temporarily stores stormwater runoff

• Key components include:– Control structure– Inflow– Detention structure– Outfall

Picture: Georgia Stormwater Management Manual 3.4-15, figure 3.4.3-1 “Example Underground Detention Tank System”

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• Detention Pipe/Vault Types: – Corrugated Metal Pipe (CMP)– Concrete pipe– Box culvert– HDPE (High-density Polyethylene)– Large concrete vault

NOTE: Some of these photos may show deficiencies as well as pipe/vault types.

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• Control Weir & Orifice Types:– Concrete– CMP Half-Round– Multiple orifices

NOTE: Some of these photos may show deficiencies as well as control weir/orifice types.

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• “TRUGS”Some UGs include underground trenches, composed of a perforated pipe within an aggregate bed or a plastic modular structure, both meant to incorporate groundwater infiltration capabilities into the facility.

Perforated pipe with aggregate bed design examples:

Modular, stackable design

Perforated CMP Concrete with drilled holes

NOTE: Some of these photos may show deficiencies as well as TRUG design types.

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Deficiencies Requiring ActionPipes (Sediment/Debris Accumulation)

Debris and sediment accumulation inside pipes

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Pipes (Damage and Deterioration)

Damage and/or deterioration inside pipes

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Pipes (Damage and Deterioration, Continued)

Spalling and exposed rebar Spalling and deterioration of control structure’s outflow pipe

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Pipes (Damage and Deterioration, Continued)

Patching brick work around pipes…

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Control Structure (Sediment/Debris Accumulation and Concrete Damage)

Trash/debris/sediment in control structure

Standing water after several dry weather days indicates a

flow blockage

Deterioration and spalling around control

structure

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Orifice Blockage and Missing Components

Downstream view of orifice blockage

Upstream views of orifice blockages

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Trash Rack and Orifice Plate (Blockages, damage, missing components, etc.)

Sediment build-up, looking upstream through the orificePonded water suggests a possible

orifice blockage

Debris blocks trash rack

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Above Ground Facilities-Underground Detention (UG)

• Common Remedies– Remove all flow blockages as well as any additional trash, debris, and

accumulated sediment• Special attention should be given, as required, to a thorough

vacuum and Hydrojet of the interior of structure– Repair/replace any damaged/missing components

• Components vary by facility type and design, and they can range from parts to structural to environmental materials (see prior noted examples)

– Check plans for specific facility requirements– Rebuild/stabilize any areas with erosion, cave-ins, and bare spots:

• Cave-ins require additional investigation to determine cause and prevent re-occurrence

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MSMD/DPWES

Above Ground Facilities-Underground Detention (UG)

• Common Remedies– Repair/replace any damaged/missing components (continued)

• For damaged/misaligned pipes:– Reinforce/repair, if possible (Internal bands and gaskets)– Slip-line pipes when possible– Excavate and replace/reseal, if first two options are not possible

– Obtain appropriate Confined Space Certification for applicable systems

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MSMD/DPWES

Below Ground Facilities-Sand Filters (SF)• Provide water quality control by

filtering stormwater through a gravel and sand bed

• Components of different sand filter types:– D.C. Sand Filter (In-Line)– Delaware Sand Filter (Side-by-Side) – Austin Sand Filter (Above-Ground)

Filter chambers in good condition

D.C. SAND FILTER

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Below Ground Facilities-Sand Filters (SF)

• Components of Different Sand Filter Types:

Filter chambers in good to moderate condition

Sediment Chamber

Clearwell

Filter Chamber

Delaware Sand Filter

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• Components of Different Sand Filter Types:

Sediment Chamber

Austin Sand Filter

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Below Ground Facilities-Sand Filters (SF)Deficiencies/Conditions Requiring ActionSedimentation and Filter Chambers (Trash/debris accumulation)

Debris in the Sedimentation ChamberTrash and sediment accumulation in the Filter Chamber - If a filter chamber is still

holding water after three days of dry weather, it is likely clogged or blocked.

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Dewatering Valves (open or missing)Dewatering valves must remain CLOSED, except during maintenance activities or the facility will be non-functional.

Valve not fully closed One of the valves has fallen off and is lying on

the chamber floor

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Dewatering Valves/Confined Space

What are some of the safetyconcerns and improper practices shown in this picture?

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Filter Media (Uneven)

These photos are all from the same sand filter facility.

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Above Ground Facilities-Sand Filters (SF)

• Common Remedies– Remove all flow blockages as well as any additional trash, debris, and

accumulated sediment• Special attention should be given, as required, to a thorough

vacuum and Hydrojet of the interior of structure• Do not Hydrojet the filter chamber

– Removal/replacement of top layer of filter bed may be required

– Repair/replace any damaged/missing components • Components vary by facility type and design, and they can range

from parts to structural to environmental materials (see prior noted examples)

– Check approved site plans for specific facility requirements

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MSMD/DPWES

Above Ground Facilities-Sand Filters (SF)

• Common Remedies– Repair/replace any damaged/missing components (continued)

• For damaged/misaligned pipes:– Reinforce/repair, if possible (Internal bands and gaskets)– Slip-line pipes when possible, as this may be most cost effective– Excavate and replace/reseal, if first two options are not possible

– Rebuild/stabilize any areas with erosion, cave-ins, and bare spots:• Cave-ins require additional investigation to determine cause and

prevent re-occurrence– Obtain appropriate Confined Space Certification for applicable systems– Maintenance for Austin sand filters may be similar to that for a dry pond

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Below Ground Facilities-Manufactured BMPs (MB)

• A pre-fabricated stormwater treatment structure utilizing one or more of the following to remove pollutants from stormwater runoff:– Settling– Filtration– Absorptive/adsorptive materials– Vortex separation– Vegetative components

• There are many kinds of MBs, which fall into two types:– Non-proprietary (public-domain)– Proprietary (patented or factory-made*)

• Follow manufacturer’s maintenance recommendations, which may require the contractor to be certified to perform the maintenance

* Note proprietary MBs are attributed (to the extent possible) to the patent holder as identified at the time of training material preparation. The following examples are commonly available/utilized technology. The inclusion of these products as examples for training purposes does not constitute any real or implied endorsement of these products by Fairfax County.

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Example of a non-proprietary Oil-Grit Separator:

Picture: US Department of Transportation, Stormwater Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring, Fact Sheet: Oil/Grit Separator Units”, https://www.environment.fhwa.dot.gov/ecosystems/ultraurb/3fs12.asp

https://www.environment.fhwa.dot.gov/ecosystems/ultraurb/3fs12.asp



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• StormFilter Components (Plan Detail for MB0173)

Inlet Bay

Cartridge Bay

Outlet B

ay

www.conteches.com

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• StormFilter Components

ABOVE: StormFilter cartridge

RIGHT: 33+ cartridges during installation

www.conteches.com

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Energy dissipater or level spreader is located at the upstream end of the

cartridge bay

www.conteches.com

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Flow spreader

www.conteches.com

Underdrain pipes

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StormGate directs low flows toward the StormFilter while allowing higher flows to bypass

StormGate

www.conteches.com

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• Proprietary MB-Vortech Stormwater Treatment SystemHydrodynamic Separation

www.conteches.com

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• Proprietary MB-Stormceptor

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• Proprietary MB-Downstream DefenderHydrodynamic

Separation

http://www.hydro-int.com/us/products/downstream-defender

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• Proprietary MB- StormTreat System

www.stormtreat.com

Bio-Media Filtration

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Deficiencies/Conditions Requiring ActionAccumulated Trash/Debris/Grit/Sediment/Floatables

Collected grit, sediment, and floatable debris in the Oil/Grit

Separator

Regular maintenance is required to remove collected materials like these

Trash, sediment, and debris in the StormFilter

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Spalling/Deterioration/Damage to Components

Spalling and exposed rebar around pipe end, inside chamber looking downstream

toward outfall

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• Common Remedies• Proprietary MBs

– Follow Manufacturers Guidance/Recommendations• Non-Proprietary MBs

– Remove all flow blockages as well as any additional trash, debris, and accumulated sediment

• Special attention should be given, as required, to a thorough vacuum and hydrojet of the interior of structure

– Repair/replace any damaged/missing components • Components vary by facility type and design, and they can range

from parts to structural to environmental materials (see prior noted examples)

– Check plans for specific facility requirements

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MSMD/DPWES


• Common Remedies• Non-Proprietary MBs (continued)

– Repair/replace any damaged/missing components (continued)• For damaged/misaligned pipes:

– Reinforce/repair, if possible (internal bands and gaskets)– Slip-line pipes when possible, as this may be most cost effective– Excavate and replace/reseal, if first two options are not possible

– Rebuild/stabilize any areas with erosion, cave-ins, and bare spots:• Cave-ins require additional investigation to determine cause and

prevent re-occurrence– Cut back overgrown vegetation around facility structures to facilitate

access and proper function– Obtain appropriate Confined Space Certification for applicable systems

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MSMD/DPWES

Above Ground Facilities-Rooftop Detention (RT)

We will finish up with Vegetative Practices after a short

BREAK…

Contractor Awareness Training Below Ground Facilities 2016

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