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CONCLUSIONS AND RECOMMENDATIONS In summary, this investigation has found the Site suitable for the use of on-site septic systems; the soil conditions examined near the proposed septic system drain fields were found to be suitable. Satisfactory soil percolation rates of 2.38 and 2.19 min/in were observed in the shallow soil zone at the test locations. The depth of ground water based on recent aquifer levels is estimated to be 25 to 30 feet below ground surface; the well completion report for the new domestic well indicates a depth to water of 32 feet. The ground-water flow beneath the Site is to the north or north-northeast at a rate of approximately four feet per mile. Because the percolation rate encountered falls between 1.0 and 5.0 min/in, the San Joaquin County Environmental Health Department will require a 20-foot separation from the bottom of the dispersal system to ground water, or mitigation by system design or enhancement. Based on the predicted current depth to water, no modification to standard, shallow systems should be required. A water sample was collected from the old domestic well on the Site as part of this investigation; the new well is not currently operational. Nitrate was detected in the sample at a concentration of 22.6 mg/L-N, above the MCL of 10 mg/L-N. DBCP was not detected in the sample; the MCL for DBCP is 0.2 ug/L. It is recommended for health reasons that bottled water be consumed until the concentration of nitrate can be reduced to below the MCL. Nitrate can be removed by filtration, and several whole- house filters are available. When the new well is made operational, it should be tested for nitrate prior to domestic use. Nitrate levels in the area may derive in part from fertilization of nearby orchards. Based on a review of the San Joaquin County Environmental Health Department's map of nitrate detections in nearby wells, two wells within a half-mile radius of the subject Site have been tested. 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 mg/L-N. One well within a half-mile radius of the Site was tested for DBCP; no DBCP was detected. Based on the current project, 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 13.0 mg/L-N. This level exceeds the US EPA drinking water recommendation of 10 mg/L-N. For greater protection of the ground water, it is recommended that only shallow septic systems utilizing leach lines or filter beds be installed rather than deeper sumps. 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 1938 Page 17