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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. A satisfactory soil percolation rate of 22.7 min/in was observed in the shallow soil zone at the test location. The depth of ground water based on recent aquifer levels is approximately 40 to 55 feet below ground surface. The ground-water flow is to the east, northeast, or southeast; the ground-water gradient beneath the Site could not be determined due to an unmapped area to the west. The highest recent ground-water levels for San Joaquin County were experienced in 1983 and 1999; however, depth to water in the Tracy area was not mapped for those years. Because of the percolation rate between 5.0 and 30.0 min/in encountered in the test hole, 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 ground water, 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 14.7 mg/L-N, over the MCL of 10 mg/L-N. DBCP was not detected in the sample; the MCL for DBCP is 0.2 ug/L. According to the original permit, the well has a grout seal at a depth of 50 feet. It is recommended for health reasons that bottled water be consumed until the concentration of nitrate can be reduced to below the MCL. Mr. Lopes indicated that he already purchases bottled water to drink, and that he employs a water filter for other domestic water uses. Based on a review of the San Joaquin County Environmental Health Department's map of nitrate detections in nearby wells, five wells within a half-mile radius of the subject Site have been tested for nitrate. Three of these wells were found to contain nitrate at a concentration greater than 10 mg/L-N, one contained nitrate at a concentration between 5.1 and 10 mg/L-N, and one contained nitrate at a concentration between 0.1 and 5.0 mg/L-N. According to the DBCP map, two wells within a half-mile radius of the Site have been tested for DBCP; no DBCP was detected in either well. 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 12.2 mg/L. However, based on the conservative nature of the calculation, depth to water, and clay soil present in the area, the actual impact to ground water may be considerably less. LOGE 20-05 Page 15