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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic system drain field area appear to be suitable. Satisfactory soil percolation rates of 5.6 min/in, 6.9 min/in, and 17.86 min/in were observed in the test locations. The soil was found to be clay and silty clay. Each percolation test is considered applicable to an area approximately 100 feet in radius. The depth of ground water based on recent, mapped aquifer levels is approximately 30 to 32 feet below the ground surface, depending on the season. The ground water flows predominantly toward the north at a rate of approximately zero to eight feet per mile in the vicinity of the Site. Because of the percolation rate between 5.0 and 30 min/in encountered, 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 predicted depth to ground water, no modifications to standard septic systems should be necessary to satisfy this requirement. A water sample was collected from the eastern domestic well on the Site as part of this investigation. Nitrate was detected in the sample at a concentration of 4.7 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. As indicated on the San Joaquin County Environmental Health Department's map of nitrate detections in nearby wells, two wells within a one-mile radius of the subject Site have been tested for nitrate. Both of these wells were found to contain nitrate at a concentration greater than 10 mg/L-N. According to the DBCP map, one well within a one-mile radius of the Site has been tested for DBCP; no DBCP was detected. As calculated for the current project, the use of on-site septic tanks and drain field systems on the Site is predicted to cause a buildup of nitrate in the aquifer up to 42.6 mg/L-N. This level exceeds the US EPA drinking water recommendation of 10 mg/L-N. The Hantzsche and Finnemore equation is a conservative method for determining potential impacts, and actual nitrate loading experienced on the Site over time may be less than predicted. Based on the result of the nitrate loading calculation, use of a septic system that has been engineered to reduce nitrate in the effluent is recommended for the proposed development. The San Joaquin County Environmental Health Department can provide specific guidelines for the degree of nitrate mitigation required. LOGE 1947 Page 15