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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 utilizing leach lines with seepage pits. A satisfactory soil percolation rate of 4.6 min/in was observed in the shallow soil zone at the test location. The soil in the test location was found to be clay and sandy silt. The depth of ground water based on recent aquifer levels is approximately 70 to 80 feet below ground surface. The ground -water flow is to the northeast at a rate of approximately 40 to 70 feet per mile. Because of the percolation rate between 1.0 and 5.0 min/in encountered in the test hole, the San Joaquin County Environmental Health Department will require a 20 -foot separation from the bottom of the dispersal system to ground water, unless mitigated by system design or enhancement. Given the estimated depth to water, no modification to a standard system should be necessary to fulfill this requirement. A water sample was collected from the northern domestic well on the Site as part of this investigation. Nitrate was detected in the sample at a concentration of 16.3 mg/L-N, well above 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 the results of the water sample, it is recommended that residents utilizing that well consume bottled water until the nitrate levels can be brought below the MCL through filtration or well repair. Based on the methods 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 5.8 mg/L, well below the maximum drinking water standard of 10 mg/L-N. As discussed above, the existing nitrate levels in the northern domestic well currently exceed the MCL. Based on the favorable result of the nitrate loading calculation, no nitrate mitigation will be required for the proposed septic system at this time. LOGE 2211 Page 14