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7Thi.,ssts that the denitrification potential within the soil profile may not be as high as if theogen concentrations actually decreased with increasing depth. Since organic matter is promotion of denitrification, and organic matter increased with depth, the nitrate-nitrogen content might have a higher potential than the 6 ppm observed. Because 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 alkaline which may have an effect on ammonium formation and stability. The CEC measures the ability of the soil to theoretically trap and hold ammonium molecules. Cation Exchange Capacities of the soil samples are comparatively high due to the clay content. This means there is a high potential for the retention of ammonium molecules for microbial uptake, and denitrification potential. This is what may be occurring at all of the tested depths, because when the nitrate-nitrogen concentrations of the tested samples are compared to other samples in the Tracy area, we find these tested concentrations to be lower. NLS§ 3.3, SSS 5.3 Table 1 below summarizes the surface and subsurface soil characteristics encountered fro e four soil samples, particularly illustrating the sand, silt and clay content percentages of each sample: TABLE 1 - SOIL PROFILE CHARACTERISTICS AND . ANALYTICAL TEST RESULTS. 'SAMPLE DEPTH.AND SAND,SILT AND SOIL', SOIL NITROGEN pH AND (SAMPLE NUMBER ON CLAY CLASSIFICATION CONTENT CATION EXCHANGE TEST RESULT FORM) PERCENTAGES CAPACITY 24 IN DEPTH 51%,24%,24% Sandy Clay Loam 4 ppm NO3-N 7.7 21.1 meq/100g (24 IN) 40 IN DEPTH 51%,24%,24% Sandy Clay Loam 3 ppm NO3-N 8.2 22.6 megl100g (40 IN) 72 IN DEPTH 61%,24%, 15% Sandy Loam 6 ppm NO3-N 8.3 18.9 meq/100g (72 IN) 92 IN DEPTH 75%, 14%, I l% Sandy Loarri 6 ppm NO3-N 8.3 12.8 meq/1008 (92 IN) C. PERCOLATION TEST RESULTS SSS§ 6.2. To assess the permeability capabilities of the on-site soils, the aforementioned two percolation test borings were completed in the locations depicted in the Site Plan found in Appendix C. The test depths at 24 and 40 inches below existing grade give a comparatively detailed observation of subsurface permeability at these two strata. Only the 40-inch test depth is recognized as "official"by EHD, while the 24-inch depth gives data on shallow percolation. The test depths can be considered to represent the average permeability throughout the effluent receiving soil profile. I 4 Chesney Consulting