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` There will be a septic tank for each house and each tank should have two compartments and be 1,200 gallons in size. An effluent filter may be installed in the second compartment of each tank. The percolation test results reveal surprisingly good percolation considering the clay soil content at a depth of 42 inches below grade. Hydraulic conductivity testing indicates an application rate of 12.8 gallons/sq ft/day, which can be considered excellent. Seepage pits and sumps will not be allowed by the San Joaquin County Environmental Health Department. Sumps and pits may be the main culprit for nitrate impact originating from septic systems in this locale. This assumption is due to the fact that these structures are dug or drilled into the underlying gravel strata, which is substantial under the Valpico Section. Consequently, the favorable soil characteristics of denitrification described above and proven analytically, cannot act upon the effluent once it enters the sumps or pits. Depending upon the final design criteria imposed by the Environmental Health Department for effluent management, the leachfield criteria could be based upon the following: 1.) The leachfield area based upon the percolation rate obtained as stipulated in Section 10.3.4 of the San Joaquin County Sewage Standards. Since the perc rate was 11.9 min/in,the leachfield area translates to 8,000 sq ft under this Section. This leachfield area would translate to an additional 4,000 sq ft for reserve area, for a total of 12,000 sq ft. The orientation of the reserve area in relation to the primary leachfield can be determined by the plumber and septic system installer once elevations have been determined. It is my understanding the new house is to be raised floor; therefore, elevation matches may be achieved without having to pump the effluent. A 14,476 sq ft primary and replacement area has been illustrated on the attached schematic. 2.) The permeability of the soil in the leachfield area will theoretically reach a conservative long term application rate (LTAR) of septic effluent of approximately 0.25 gals/ft'/day due to biomat formation. Although the hydraulic conductivity test indicates a theoretical application rate of 12.8 galslft2/day, 0.25 gals/ft2/day is a safety factor of 50 and therefore, conservative. As noted below, if there are a total of six - 100 foot leachline trenches, and only one sq ft on each side of the leachline trench will accept effluent(this excludes the floor of the trench for a safety factor), then there will be: 200 sq ft/trench x 6 trenches total = 1,200 sq ft of application area. If the LTAR is 0.25 gals/ft'/day, then the trench sidewalls should accept: 1,200 ft2 x 0.25 gals/ft2/day = 300 gallons/day. In Section C above, 220 gallons/day was determined from the calculations. 3.) The leachfield area calculated from the Iineal foot required as calculated in Section 8.6 of the Sewage Standards for each house: 1,200 gals BTC + gals 220 ADF (ADF doubled) = 1,420 CTC x 0.225 = 320 lineal feet of leachline. Use three - 100 foot leachlines for each house. There is sufficient reserve area with a total of six leachlines. 4.) The leachfield area is currently planted in apricots. The Sewage Standards state that leachlines must be 10 feet away from large trees. If the.sewage contractor can work this distance requirement into the orientation of the leachfield,then the trees may be beneficial for nitrogen uptake. Page -8- Chesney Consulting