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r�" The project site has relatively level terrain; consequently, there will be no need to incorporate design considerations for slopes within the disposal area. Under EHD requirements and regulations, 'a mound system for effluent disposal is typically required in this locale due to the clayey soils and more particularly,the high groundwater table. Mound systems are sensitive to sloping, and changes in design must be taken into consideration when natural ground sloping is present. It is imperative that during the preparation of the indigenous soil surface where the mound system is to be installed, be absolutely level. Septic tank usage and disposal parameters will be discussed in a design report for this facility. i B. SOIL PHYSICAL CHARACTERISTICS AND ANALYTICAL TEST RESULTS The United States Department of Agriculture - Soil Conservation Service (USDA-SCS) indicates the , on-site soils to consist of Capay clay(#118). SSS§ .2. The surface and subsurface soil investigation and testing began on February 14, 2007 with llin 24-inch, and a 40-inch deep percolation borings.in the proposed effluent disposal area using a truck-mounted drill rig. This disposal area is denoted on the Site Plans found in Appendix A. Soil cutting samples from the bottom of these two borings were retrieved for chemical analysis, asJwell as a sample from the soil surface. On February 19, 2007, a backhoe became available to sample soil at deeper depths. Samples from 59 inches and 77 inches in depth were retrieved. At the 77-inch depth, saturated soils conditions were encountered and groundwater seeped into the test pit. After waiting one hour, the depth to standing water within the test pit was 4.5 feet below the ground surface. The test pit was then subsequently closed in. NLS§ 1.1 12.�As the noted on the A&L Laboratory Soil Analysis Reports, chemical analyses.,of the five soil samples quantify several constituents that influence nitrate loading from this project. The important parameters for nitrate loading assessment are the organic matter, pH, cation exchange capacity(CEC), clay content percentage, along with nitrate-nitrogen content of the soil. Total Kjeldahl Nitrogen(TKN) content was also measured because it shows the organic and ammonium fractions of the tested soil samples and provides a baseline for potential future comparisons of soil samples from under the wastewater disposal system. As noted, the organic matter in the surface soils is very high and continues to decline in the subsequent deeper depths. A high surface soil organic matter may be attributable to native vegetation. The TKN results reveal very high concentrations at the surface,but decline precipitously down to 77 inches in depth. This suggests a lower potential for future nitrate-nitrogen loading from indigenous nitrogen soil content. The nitrate-nitrogen concentrations are low-to-medium. At',24 inches, the concentration is medium, then decreases at the 40-inch depth, increases again at the 59- inch depth and then substantially decreases at the 77-inch depth. This suggests a high denitrification potential between the surface and the 6.5 foot depth. Organic matter is needed for promotion of denitrification and since the TKN is high in the shallow soils, denitrification potential may also be high in these soils. 3 j i Chesney Consulting