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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 standard septic systems. A satisfactory soil percolation rate of 10.4 min/in was observed in the shallow soil zone at the test location. The soil in the test area was found to be clay and silty clay. The percolation test is considered applicable to an area approximately 100 feet in radius. The depth of ground water based on recent aquifer levels is approximately 18 to 40 feet below ground surface. The ground-water flow beneath the Site is to the northwest at a rate of approximately 0 to 12 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 present a difficulty. No wells are located on the Site. No water sample was collected as part of this investigation. Based on a review of San Joaquin County Environmental Health Department map of nitrate detections in nearby wells, it appears that seven wells within a one-mile radius of the subject Site have been tested for nitrate; it was detected in five of the wells at concentrations between 5.1 and 10.0 mg/L-N, and in two of the wells at concentrations between 0.1 and 5.0 mg/L-N. According to a neighbor, the adjacent property to the north of the Site was a dairy in the past; dairies can contribute to elevated nitrate levels. 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 have the potential to cause a buildup of nitrate in the aquifer of 11.5 mg/L-N for two houses or 13.8 mg/L-N for three houses. Both results slightly exceed the US EPA drinking water recommendation of 10 mg/L-N. Due to the conservative nature of the calculation, the actual nitrate loading experienced on the Site over time may be less than predicted For protection of the ground water, it is recommended that only shallow septic systems utilizing leach lines or filter beds be installed on the Site. Recent San Joaquin County Environmental Health Department policy has been to evaluate each project on a case- by-case basis to determine whether additional measures to mitigate nitrate should be employed. LOGE 20-08 Page 13