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7denitrification on as possible to take advantage of evaporation and evapotranspiration. Deep rooted should be planted over the leachfield. The scientific literature suggests that may be enhanced by placing proposed leachlines higher in elevation toward the soil surface, particularly since the surface soils contain approximately 27% of the clay soil fraction. The north leachfield should be installed also with the leachlines high in elevation. During the rainy season,November through March, nitrification is suppressed during these colder months of the year, so it would be beneficial for the leachlines to be placed high in elevation where the soil/effluent interface is colder. Additionally, the north side of the house will not "dry-out" like the south side can during the winter months, thus keeping a higher moisture content in the soil, forcing an anaerobic environment and impeding nitrification. Blackwater may be piped to the north leachfield and graywater piped to the south leachfield. Deciduous and evergreen plants should be planted no closer than 15 ft from any leachline to prevent serious root infiltration into the leachlines. These procedures described above should theoretically provide a triple nitrate mitigation system of 1.) denitrification/clay absorption, 2.) nitrification suppression and 3.) evaporation/evapotranspiration. The two septic tanks for the dual system must have two compartments and be 2000-gallons each:. •Effluent filters must be installed in the second compartment of each tank. If elevations cannot be matched with grades, then the effluent will have to be pumped to the leachfield, in which case a filter bed design may be considered...A filter vault with a pump must be installed if the effluent , is to be,pumped. > The percolation test results reveal surprisingly good percolation considering the clay soils at a depth of 42 inches below grade. Hydraulic conductivity testing indicates an application rate of 3 gallons/sq ft/day, which can also be considered good. Seepage pits and sumps will not be allowed by the San Joaquin County Envirohmerital Health Departments 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 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 10 min/in, the leachfield area should be 6,000 sq ft. Both the north and south leachfields can be 100 ft x 30 ft= 3,000 + 3,000 = 6,000 sq ft. 2.) The leachfield area based on the permeability of the soil eventually reaching a conservative long term application rate (LTAR) of approximately 0.25 gals/ftz/day due to biomat Page -9- valley AB Research