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a ;C Applications on file with the County Environmental Health Department reveal that there have been five permits issued for repairs/additions to existing systems in the one-half mile study area, primarily for additional drainage. This can be regarded as a medium number of repairs/additions, and can be attributed to the clay soil structure existing at typical leachline depths. B. SOIL PHYSICAL CHARACTERISTICS AND ANALYTICAL TEST RESULTS The project site has level terrain; consequently, there will be no need to incorporate design considerations for slopes. The United States Department of Agriculture - Soil Conservation Service (USDA-SCS) indicates the on-site soils toconsist of a Capay Clay- Urban Land t Complex (122). This soil unit contains 50% Capay clay which correlates with the soil texture test results (55%). A 9-ft hand boring was completed at the south side of the Carmelo Avenue cul-de-sac as requested by the Environmental Health Department. This boring provided 1.) a profile of the underlying soil characteristics, 2.) depth to groundwater and 3.) a water table sample. The top groundwater sample was analyzed to quantify impact from a failing leachfield located in the southwest corner of the project site. t The log of boring illustrates the subsurface soil characteristics encountered: The surface soils to 0.5 feet consist of a light brown silty clay with gravel fill. Below this strata and extending to 4 ft is a dark brown, tight clay with consistent moisture. From:4 ft to boring termination at 9 ft, the F soil consists of a yellowish brown silty clay with a higher moisture content. At 7.5-8.0 ft is the capillary fringe with the zone of saturation at 8.0 feet. The static water level was 7.6 ft. No rust mottling was observed which would be indicative of seasonal soil saturation. 1 A soil sample was obtained from the proposed north leachfield (N.L.F.) area for chemical analyses, from a depth of 24 inches. As the noted on the SOIL ANALYSIS REPORT, the nitrate-nitrogen (NO3-N) concentration at the 24-inch depth elevation is 11 ppm. This concentration can be considered low and will have inegligible impact on the underlying groundwater. Additional chemistry of the soil sample was also done to analyze several constituents. The { important parameters for nitrate loading assessment are the organic matter,pH, cation exchange i capacity(CEC), clay content percentage, along with nitrate-nitrogen content. As noted, the { organic matter in the soil is also low. This also indicates a very low potential for future nitrate- nitrogen loading. Since septic effluent is composed predominately of ammonium (NH4), the pH, along with the CEC, are significant influences on ammonium molecules. The pH of the soil is relatively alkaline which may slightly inhibit ammonium formation and stability, and may create a small propensity for ammonia(NH3) formation. The CEC measures the ability of the soil to � p P Y � Y theoretically trap and hold ammonium molecules. A CEC of 26.0 suggests there is considerable potential for the retention of ammonium molecules�for microbial uptake, and suppression of nitrification (nitrate formation). 2 ,I Chesney Consulting 1