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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic system drain field were found to be suitable for a shallow septic system utilizing leach lines or a filter bed. A satisfactory soil percolation rate of 5.32 min/in was observed in the shallow soil zone at the test location. The depth of ground water based on recent aquifer levels is approximately 28 to 40 feet below ground surface. The ground-water flow beneath the Site is to the north or northeast at a rate of approximately six to 13 feet per mile. Depth-to-water data were not available for the vicinity of the Site during the 1983 and 1999 high-water seasons. Because the percolation rate encountered falls between 5.0 and 30.0 min/in, the San Joaquin County Environmental Health Department will require an eight-foot separation. from the bottom of the dispersal system to ground water. Based on the anticipated depth to water beneath the Site, this requirement should not necessitate modifications to a standard, shallow system. A water sample was collected from the domestic well on the Site a$.:,part of this investigation. Nitrate was detected in the sample at a concentration of 6.2 mg/L-N, well below the MCL of 10 mg/L-N. DBCP was not detected in the sample. \,— Based Based on a review of San Joaquin County Environmental Health Department maps of nitrate and DBCP detections in nearby wells, four wells within a half-mile radius of the subject Site have been tested for nitrate; it was detected in two at concentrations between 0.1 and 5.0 mg/L-N, and in the other two at concentrations between 5.1 and 10.0 mg/L-N. Three wells within a half-mile radius of the Site were tested for DBCP; no DBCP was detected in any of the wells. Based on the method and assumptions described, the nitrate loading calculation indicates that the use of on-site septic tanks and drain field systems on the Site has the . potential to cause a buildup of nitrate in the aquifer of up to 16.2 mg/L-N, above the US EPA drinking water recommendation of 10 mg/L-N. However, based on the conservative nature of the calculation, clay soil present in the area, and lack of nitrate detections above 10 mg/L in nearby wells, the actual nitrate impact likely will be less than calculated. Nevertheless, it is anticipated that the San Joaquin County Environmental Health Department may request the new septic system be modified for nitrate reduction. LOGE 1925 Page 13