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B. SOIL PHYSICAL CHARACTERISTICS AND ANALYTICAL TEST RESULTS The project site consists of level terrain; consequently,there must be no design considerations for slopes for a future septic system. A stormwater detention pond has been excavated at the back or east end of the project site. From this excavation, it is was possible to obtain an ideal examination of the underlying soil strata to a depth of 18 feet. A log of boring found in the Appendix illustrates the subsurface soil characteristics. The surface soil (0-3') is composed of a fine sandy silt/silty sand. From four to six feet, there exists a severe cemented silts hardpan with extremely slow permeability. Beginning at approximately five and one-half feet, there is a compressed silty sand layer. The silt is not cemented, but comparatively tight with a surprising degree of permeability, considering the small pore size of the soil. The soil is progressively sandier with depth. A feature of the soil observed in this excavation was rust mottling of this sandy silt/silty sand _ strata. This can be attributed to geologic processes, it may be this mottling originates from seasonal soil saturation. Rust mottling occurs when anaerobic bacteria decompose organic matter and use oxidized iron in their metabolic processes. If these two conditions are present- - organic matter and an anaerobic environment, denitrification(the conversion of nitrate to gaseous products and the primary means by which nitrate concentrations are reduced) is promoted. A soil sample was obtained near the existing leachfield which will serve as the office. Chemical analyses of soil composited from the 24 to 36 inch depths was done to quantify several constituents. The important parameters for nitrate loading assessment are the organic matter,pH, cation exchange capacity (CEC), and nitrate-nitrogen(NO3-N) content. As noted,the organic matter in the soil is low and indicates a potentially small influence on additional nitrate-nitrogen loading in the future. Previous organic matter content from past agricultural activity has apparently been oxidized. The pH of the soil is alkaline which may slightly inhibit ammonium (NH4)formation and stability. The CEC measures the ability of the soil to theoretically trap and hold ammonium molecules. A CEC of 11.7 indicates there is limited potential for the retention of ammonium molecules for microbial uptake. C. PERCOLATION TEST RESULTS The perc tests were conducted on April 2, 1999 under U.S.E.P.A. and San Joaquin County Environmental Health guidelines near the existing building to be used as an office. Since the soil at the perc test depth of 40 inches is sandy, and six inches of water seeped away after one-half hour,the test was conducted over a two-hour period to ensure complete soil saturation and observe any influence from the underlying hardpan layer. As illustrated on the attached Field Percolation Testing Report, the perc rate remained relatively constant throughout the test period. The depth at which the perc test was done represents effluent percolation which normally takes place at the bottom of a leachline trench. The perc test results indicate rapid percolation of approximately 7.5 min/in at the shallow test depth. 2 Naffey Aq Pesearch