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j samples, there was virtually no ammonia-nitrogen, or NH4 ions. Two explanations for this include the pH of the soil, which is somewhat alkaline and may inhibit ammonium formation and stability. Secondly, the CEC measures the ability of the soil to theoretically trap and hold ammonium molecules. The clayey surface soils have a comparatively high CEC of approximately 19, which should increase the retention of ammonium molecules for microbial uptake and suppression of nitrification (nitrate formation). In cation exchange, a positively charged ion within the clay complex is replaced and released by another type of ion. Ionic exchange, through its effects on nutrient availability and acidity, has a tremendous effect on biological and chemical transformations. The significance of cation exchange becomes important when the chemistry of septic effluent is analyzed. Nitrogen in septic tank effluent consists of approximately 75%N in the ammonium ion(NH,') form and 25%N in the organic form. If the ammonium, ion is bound and eventually utilized, nitrification cannot occur. The organic fraction of the soil, as determined by TKN, reveals that the soils are normal, and based on my observations, are concentrations typically found in agronomic soils (soils that are agronomically viable). The results of the soil nitrate-nitrogen concentrations'were interesting. fAi ili6-62-in. depth, the NO3-N concentration was i10 ppm, but decreased for 8 ppm at the 92 in.'and 12 ft depths. The soil sample from the future leachficld at the 42 in. depth tested at 7 ppm.NO3-N, indicating a slightly lower indigenous NO3-N content than what was determined under the leachline. In addition, there was also no ammonia-nitrogen, and the TKN concentration was equivalent to the 92 in. depth sample, which was the highest concentration. If it were possible to collect sufficient vadose zone water, the same nitrogen concentrations would probably be observed. 2. SUBSURFACE SOIL HYDRAULIC CONDUCTIVITY In addition to the conventional perc tests described below, hydraulic conductivity data of the shallow soils from zero to 24 inches in depth was obtained and is illustrated on the FIELD PERCOLATION TESTING REPORT. After four hours of testing, it was determined that the shallow soils absorb 1,200 cc/hr. This is equivalent to 0.00528 gal/min or 7.6 gallons/day. Since the internal area of a 24-inch deep x 4.5 inch dia. boring is 355 int or 2.5 ft2, the application rate for the surface soils is theoretically 3.0 gallons/ftz/day. C. PERCOLATION TEST RESULTS The percolation test was conducted on September 28, 2001 under U.S.E.P.A. and San Joaquin County Environmental Health guidelines. Since the soil type at typical leachline depth of 42 inches is a clay soil, the test period was four hours in duration. As indicated on the attached FIELD PERCOLATION TESTING REPORTS, the perc rates for the test boring reveals comparatively rapid perc rates considering the clay soil. This may be attributed to soil cracking which is -- of clays. The test results are summarized below: Page -3- Nafley gig Research