Fred Vengrouskie Alabama Department of Public Health

Onsite Program EvaluatorSoil & Onsite Sewage Branch

Division of Community Environmental Protection

420-3-1-.67 Lot Modification and Controlled Fill Systems(1) In the event that, due to site conditions and/or characteristics of a given lot, a Conventional OSS cannot be used in accordance with the preceding requirements of these Rules, the LHD may consider approval of plans for the installation of a Controlled Fill OSS or certain Lot Modifications. Controlled Fill designs may be considered only on sites where the fill selection, placement, natural ground surface preparation and the entire Controlled Fill construction process will be performed under the direct supervision of, and certified by, a professional engineer.

(a) Site Evaluation - Prior to placing the fill, the site shall be evaluated in accordance with the Site Evaluation Criteria of the Onsite Rules.

(b) Design Calculations – The engineer must submit the design calculations for the designed systems size and specifications.

420-3-1-.71 Site Limitation Determination (SLD)

Site evaluations may be preformed using:

percolation test*soil morphology unified method*soil mapping

* Testing methods approved for Professional Engineers

Example: To design a basic controlled fill septic system for a 5 bedroom house on a building site that has a 60 MPI perc rate and a restriction of ASHES at a 24” depth

First determine the design flow:

Design Flow = Number of bedrooms X 150 gallons per bedroom(Table 1)

Design Flow = 5 X 150 = 750 gallons

Design Flow for dwellings

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Presentation Notes

Note: Pump tanks and grease traps are not to be used in calculating hydraulic detention time. The only break from this requirement is when treating to secondary standards.

Number of bedroomsX

“Square Feet per Bedroom” in Table 3 and Table 3a

that corresponds to the measured or assigned percolation rate

The linear amount of 36” wide gravel field line is determined by multiplying the number of bedrooms by the square feet per bedroom for the Soil Texture Group/Perc Rate from Table 3 and then dividing by 3.

Amount of field line = 5 X 300 ft2 = 1500 ft2

Linear feet(36” wide) = 1500/3 = 500 linear ft

Square feet per bedroom

Linear feet per bedroom(36”)

Determine the Minimum Vertical Separation

For a 60 MPI perc rate the Minimum Vertical Separation (MVS) is currently 24”(Table 15).

Note: The MVS for a 31 to 60 rate is currently proposed to changed to 18”

Controlled Fill Systems or Mound designs for sites with any limiting zone which will require trench bottoms to be located at 0 to 6 inches above the natural ground surface shall, as a minimum, have 6 inches of fill material below the trench bottoms.

* Does not apply to Drip

Trench Profile

Ex: Restrictive Zone 24” ASHES @ 60 min/in

12”

Natural Ground

6”

24”Restriction

Fill

Basal Area

Absorption Area

Distribution AreaReduced Distribution Area

Reduced Absorption Area

Styrofoam aggregate Multi-pipe

Chambers

The amount of EDF pipe as required in Table 3 or Table 3a (DA)Required separation distances (5 feet from sidewall to sidewall) between the EDF trenches and the distance (5 feet) from the trench ends or outer sidewalls to the beginning of the Controlled Fill bed side/endslope (AA)Fill height and slope (3:1 or greater)

http://www.toolbase.org/techinv/products/SubstituteAggregateLeachField.jpg

MVS changes from 24” to 12”A 30” high system is reduced to 0” because of the MVS break for secondary treatmentNo requirement to keep the field lines 6” above the natural ground surface for drip.The system requires much less landscaping and drainage work

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Presentation Notes

I included, in your handouts, the primary tables mentioned in the Engineered Checklist. Table 10 in Appendix A of the onsite rules shows the infiltration rates used for sizing drip disposal fields. An example on how to use the table is shown.

Required total area sq. ft.(DA) = 750gal/.2 = 3750 ft2 = 1875 linear ft of tube/2 - 1000’ zonesNo fill required with tubing installed at a 6 to 12 inch depth but effluent must be treated to secondary standards

Using LPP will reduce the controlled fill system footprint

Provides equal distribution of effluent

Required total area ft2(DA) = 750gal/.4 = 1875 ft2

Absorption Area(AA) = (19+4) x (100+4) = 23 x 104 = 2392 ft2

Basal Area(BA) =(23+(2(3)(2.5))) x (104+(2(3)(2.5)))=(23+15)x(104 +15)= 38 x 119 = 4522 ft2

MVS changes from 24” to 12”A 30” mound is reduced to 18” because of the MVS break for secondary treatmentRequires less landscaping and drainageSmaller mound footprint

Required total area sq. ft.(DA) = 750gal/.6 = 1234 ft2

Absorption Area(AA) = (13 + 4) x (100 + 4)= 17 x 104 = 1768 ft2

Basal Area(BA)=(13+ 2(3)(1.5))x(104+2(3)(1.5)) = (13 +9) x (104 +9) = 22 x 113 = 2486 ft2*

*Smallest footprint allowed in current rules

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Presentation Notes

Look at page 1 of the Checklist for Engineered systems. Page 1 of this checklist applies to the review of all engineered systems and contains the items discussed during my previous presentation.

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Presentation Notes

Page 2 is to be used in addition to page 1 for the review of engineered controlled fill systems. This page of the checklist must be used according to the type of disposal product recommended in the design.

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Presentation Notes

Page 3 is to be used in addition to page 1 when reviewing a Wisconsin Mound Design System.

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Presentation Notes

The top of Page 4 is to be used in combination with pages 1 and 2 if Low pressure pipe is recommended for use in a Controll fill system. The lower portion of the page is to be used for the review of Constructed wetlands. This portion of the checklist was not changed from the previous checklist since few of these systems are currently being designed in Alabama.

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Presentation Notes

Page 5 is to be used in combination with pages 1 and 2 when Drip Irrigation is recommended.