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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions near the existing septic system drain field were found to be suitable. A satisfactory soil percolation rate of 19.2 min/was observed in the deep soil zone at the percolation test location. The depth of ground water based on recent aquifer levels is approximately 135 to 145 feet below ground surface. Ground water flows down to the south at a rate of approximately 2 to 3 feet per mile. The highest recent ground-water levels for the area were experienced in spring of 1983 and 1999; at these times, ground water would have been present at approximately 115 to 125 feet below ground surface. Because the percolation rate encountered falls between 5.0 and 30 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 depth to water in the area, no modifications to standard systems should be required. A water sample was collected from each domestic well on the Site as part of this investigation. Nitrate was detected in the sample from the western well at a concentration of 1.9 mg/L-N, in the sample from the center well at a concentration of 0.8 mg/L-N, and in the sample from the eastern well at a concentration of 0.8 mg/L-N. DBCP was not detected in any of the samples. The Maximum Contaminant Level (MCL) set by the US EPA for nitrate is 10 mg/L-N; the MCL for DBCP is 0.2 µg/L. Based on a review of the San Joaquin County Environmental Health Department map of nitrate detections in nearby wells, three wells within a one-mile radius of the subject Site have been tested for nitrate. Nitrate was detected in all three wells at concentrations between 0.1 and 5.0 mg/L-N. According to the DBCP map, two wells within a one-mile radius of the Site have been tested for DBCP; DBCP was not detected in either well. Based on the current project, the use of on-site septic tanks and drain field systems on the Site is not expected to cause a buildup of nitrate in the aquifer above 0.6 mg/L-N. This level falls well below the US EPA drinking water recommendation of 10 mg/L-N. We believe the Site suitable for the use of standard septic systems utilizing leach lines and seepage pits. Based on the satisfactory result of the nitrate loading calculation, no nitrate mitigation is recommended for the current project. LOGE 1943 Page 17