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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 6.41 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 120 to 134 feet below ground surface. In the spring map reviewed, the ground-water direction and gradient could not be determined. In the fall map, ground water flows down to the northwest at a rate of approximately three 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 95 to 106 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 fulfill this requirement. 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 7.2 mg/L-N, 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 map of nitrate detections in nearby wells, two wells within a half-mile radius of the 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 the other at a concentration between 5.1 and 10.0 mg/L. According to the DBCP map, one well within the same area was tested; DBCP was not detected in the 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 13.3 mg/L-N, above the US EPA drinking water recommendation of 10 mg/L-N. However, based on the conservative nature of the calculation, depth to water beneath the Site, existing nitrate levels in the area, and clay soil present, it is the professional opinion of Live Oak that shallow septic effluent from the subject Site is unlikely to contribute significantly to a build-up of nitrate in the ground water. Use of a standard, shallow septic system should be permitted for the new home. LOGE 1946 Page 14