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ADPH – PUBLIC HEALTH AREA VIII TRAINING FOR PROFESSIONAL ENGINEERS And Associated Onsite System Professionals
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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
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)
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
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