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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 a standard septic system. A satisfactory soil percolation rate of 25 min/in was observed in the shallow soil zone at the test location. The soil in the test area was found to be 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 34 to 46 feet below ground surface. The ground-water flow beneath the Site is to the northeast at a rate of approximately 7 to 13 feet per mile. 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, no modifications to standard shallow septic 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 6.6 mg/L-N, below the MCL of 10 mg/L-N. DBCP was not detected. Based on a review of San Joaquin County Environmental Health Department maps of nitrate and DBCP detections in nearby wells, neither constituent appears to be present over the MCL in the immediate vicinity if the Site. 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 up to 13.0 mg/L-N. This result exceeds 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. The clay soils present on the Site should offer some additional reduction due to adsorption of the nitrate ions as the percolating effluent travels downward through the vadose zone. 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 20-42 Page 14