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NITRATE-NITROGEN IMPACT MITIGATION Although it is unlikely disposal area constraints may be an issue, a filter bed should be installed, particularly if a dual system will be required by the Environmental Health Department. The San Joaquin County Sewage Standards Section 10.1 states: "Estate type zoning (R-R) shall require a double leach field system with an alternating distribution box to be installed at the time of construction." Filter beds allow the distribution piping to be installed as high in elevation as possible to take advantage of evaporation and evapotranspiration. Deep rooted grasses may be planted over the disposal area to aid in evapotranspiration and take-up nitrogen in the form of nitrate and ammonium. Deciduous and evergreen plants may be planted no closer than 15 fl from any leachline to prevent serious root infiltration. The scientific literature suggests that denitrification may be enhanced by placing piping higher in elevation toward the soil surface, particularly since the surface soils contain approximately 36% clay soil. Additionally, during the rainy season,November through March, nitrification is suppressed during these colder months of the year, so it would be beneficial for the effluent disposal area piping to be placed high in elevation where the soil/effluent interface is colder. The procedures described above should theoretically provide a triple nitrate mitigation system of. 1.) Denitrification/clay absorption, 2.)Nitrification suppression and 3.)Evaporation/ evapotranspiration. The percolation test results reveal excellent perc at 7.4 min/in., considering the clay soil percentage of 22% at a depth of 38 inches below grade. The soils are loose and not consolidated in this area. As noted, there was a 33% decrease in the perc rate from the beginning of the test, to the end of the test, four hours later. This indicates a marginal decrease in percolative capacity when the soil is saturated. Seepage pits and sumps are not allowed by the Environmental Health Department. Sumps and pits may be the main culprit for nitrate impact to the underlying groundwater 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 promoting 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 of a second unit dwelling (and/or possible repair of the existing system), the septic system and disposal area parameters could be based upon the following: 1.) Two septic tanks are required for the dual system, and should have two compartments and be 1,200 gallons each. Effluent filters should be installed in the second compartment of each tank. A filter vault with a pump must be installed if the effluent is to be pumped. Garba e osals and water .ofteners should not be installed ineeloerkt,_ Garbage disposals will increase the organic loading in the effluent, and the sodium from a water softener will bind the clay soil and destroy permeability. 2.) The leachfield area may be 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 7.4 min/in, the standard leachfield area may be_k00__x__0 s_ft. If dual systems are installed, the leachfield disposal areas can be 100 ft x 30 ft = 3,000 + 3,000= 6,000 sq ft. L /L`" =!L afage -12- Chesney Consulting