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.. B. SOIL PHYSICAL CHARACTERISTICS AND ANALYTICAL TEST RESULTS o The area of the proposed leachfields as illustrated on the attached site plan are/Mll be level with no slopes. A log of boring found in the Appendix illustrates the subsurface soil characteristics under the Phase I leachfield, directly north of the Worship/Education building. This boring was angered by hand to accurately characterize the subsurface soils. The surface soil (0-3') is composed of a fine sandy silt. From three to five feet, the soil is a silty, fine sand. Beginning at approximately five and one-half feet, there is a compressed hardpan layer composed of a fine sandy silt. The silt is not cemented, but comparatively tight with a surprising degree of permeability, considering the small pore size of the soil. This hardpan layer extends to 10 feet. From a geotechnical investigation of the subject property conducted in September, it was found _ that there are intermittent layers of silty sand/sandy silt, sandy clays and clayey sandy silts to 25 feet. A feature of the soil observed in our boring was rust mottling of this tight, sandy silt strata. This can be attributed to geologic processes, but in this case, it appears the rust mottling originates from seasonal soil saturation. There is a clay layer under this silt strata which probably impedes percolation over time,thus causing saturation and therefore, mottling. Rust mottling occurs when anaerobic bacteria decompose organic matter and use oxidized iron in their metabolic processes. Organic matter and anaerobic conditions are required for denitrification. Denitrification is the conversion of nitrate to gaseous products and the primary means by which nitrate concentrations are reduced. Chemical analyses of soil composited from the 24 and 48 inch depths under the Phase I leachfield was analyzed for several constituents. The important parameters for nitrate loading assessment are the organic matter,pH, cation exchange capacity(CEC), nitrate nitrogen(NO3) content, and the carbon to nitrogen ratio (C:N). As noted, the organic matter in the soil is low and indicates a potentially small influence on additional nitrate-nitrogen loading in the future. The pH of the soil is slightly acidic which may increase ammonium (NH4) formation and stability. Ammonium is the precursor to nitrate. The CEC measures the ability of the soil to _ theoretically trap and hold the ammonium molecule. A CEC of 10.2 indicates there is limited potential for the retention of ammonium molecules for microbial uptake,thus a greater potential for nitrate formation. The C:N ratio signifies the ability of microorganisms to utilize organic _ carbon in the promotion of the denitrification process. A ratio of 12:1 is comparatively high and beneficial for increased microbial populations. C. PERCOLATION TEST RESULTS The perc tests were conducted under U.S.E.P.A. and San Joaquin County Environmental Health guidelines near the center of the proposed area of the Phase I leachfield. As illustrated on the attached Field Percolation Testing Report, two perc test were done at a shallow depth of 42 inches and a deep test at 8.75 feet below existing grade. These depths represent effluent percolation which normally takes place at the bottom of a leachline trench and at the bottom of a sump, respectively. The perc test results reveal rapid percolation for both the shallow and deep test borings of approximately 1 min/in. 2 Vaffey Ag Ppearch