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B. SOIL PHYSICAL CHARACTERISTICS AND ANALYTICAL TEST RESULTS The project consists of level terrain; consequently, no slope design considerations were made for any of the three installed septic systems. As illustrated on the attached Site Plan, two stormwater detention ponds have been excavated at the back or east end of the project site, and at the north-center of the project. From the east excavation, it was possible to examine the underlying soil strata to a depth of approximately 10 feet. In addition to this excavation, a hand boring was also done in the area of the Lawson Trucking leachfield to a depth of seven feet. A log of boring found in Appendix E illustrates the subsurface soil characteristics. The surface soil (0-3') is composed of a fine sandy silt/silty sand. From five to six feet,there exists a cemented silts hardpan of low permeability. Under the hardpan there is a sandy silt 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 finer with depth. Rust mottling of the soil was observed in the hand boring within the sandy silt/silty sand strata above the hardpan layer. 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. Although this mottling may be attributed to geologic processes, it is probably due to seasonal soil saturation whereby percolating soil water encounters the referenced hardpan layer and accumulates. This is why it was imperative to breach this hardpan layer prior to the emplacement of all three Site Approval septic systems to allow adequate effluent percolation. The soil environment plays a crucial role in nitrate formation, as well as its environmental fate. Soil samples were obtained from the leachfield area that will serve the Lawson facility and the Devine facility. 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 nitrate-nitrogen(NO3-N) content, organic matter, pH, and cation exchange capacity (CEC). As noted in Appendix F, the nitrate-nitrogen concentrations are low for both areas. Additionally, the organic matter in the soil is also low and indicates a potentially small influence on additional nitrate-nitrogen loading in the future. Soil organic matter from past agricultural activity has apparently been oxidized. The two parameters of pH and CEC influence the ammonium molecule (NH4) which is the precursor to nitrate. The pH of the soil is very slightly alkaline and should have no effect on inhibiting ammonium formation and stability. The CEC measures the ability of the soil to theoretically trap and hold ammonium molecules. A CEC of 5.8 and 9.4 indicates there is limited potential for the retention of ammonium for microbial uptake. Soil auger cuttings from the east basin monitoring well installation were submitted for Total Kjeldahl Nitrogen(TKN)analysis. TKN measures the soil organic nitrogen fraction and the ammonia(NH3) levels. The organic fraction was measured at 233 ppm with no ammonia detected. This concentration of the organic fraction indicates past and present potential for nitrate formation. 2 JJ Val&y Ag P(Qsearch