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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. A satisfactory soil percolation rate of 10.9 min/in was observed in the deep soil zone at the test location. The depth of ground water based on recent aquifer levels is approximately 140 to 153 feet below ground surface. Ground water flows down to the northwest at a rate of approximately four feet per mile in the fall; the rate could not be calculated for the spring. 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 120 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 to address the percolation rate. Review of septic permits for the Site indicates a history of additions to both septic systems, presumably because of failures in the systems. A water sample was collected from the domestic well on the Site as part of this investigation. Nitrate was detected in the sample at a concentration of 2.4 mg/L-N, well below the MCL of 10 mg/L-N. DBCP was not detected. Based on a review of San Joaquin County Environmental Health Department map of nitrate detections in nearby wells, five wells within a half-mile radius of the subject Site have been tested for nitrate. Nitrate was detected in all five wells at concentrations between 0.1 and 5.0 mg/L-N. According to the DBCP map, two wells within a half-mile radius of the Site have been tested for DBCP; it was detected in one well at a concentration over 0.2 ,t,g/L but was not detected in the other 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 6.0 mg/L-N. This level falls below the US EPA drinking water recommendation of 10 nng/L-N. We believe the Site suitable for the use of septic systems with leach lines and seepage pits. Based on the history of septic system repair on the Site, as revealed through permit records, the customer may wish to consider oversizing the new septic system. Oversizing increases the absorption area and may reduce the need for repairs/additions in the future. Based on the satisfactory result of the nitrate loading calculation, no nitrate mitigation is recommended for the current project. LOGE 1850 Page 14