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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions near the proposed septic system drain field were found to be suitable. A satisfactory soil percolation rate of 25.0 min/was observed in the shallow soil zone at the percolation test location. The depth of ground water based on recent aquifer levels is approximately 75 to 85 feet below ground surface. Ground water flows down to the northwest at a rate of approximately five to six feet per mile in the area northwest of the Site; the gradient for the Site itself cannot be calculated because it is at the edge of the map. 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 45 to 53 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 the domestic well on the Site as part of this investigation. Nitrate was detected in the sample at a concentration of 1.8 mg/L-N, well below the MCL of 10 mg/L-N. DBCP was not detected in the sample; the MCL for DBCP is 0.2 ug/L. Based on a review of the San Joaquin County Environmental Health Department's 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 one well at a concentration between 0.1 and 5.0 mg/L-N, and in two wells at concentrations over 10 m/L-N. According to the DBCP map, one well within the same area was tested; DBCP was not detected in that well. 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 up to 9.9 mg/L-N, below the US EPA drinking water recommendation of 10 mg/L-N. We believe the Site suitable for the use of a standard septic system utilizing leach lines, leach lines with sumps, or a filter bed. Based on the satisfactory result of the nitrate loading calculation, no nitrate mitigation is recommended for the current project. LOGE 1945 Page 13