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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the existing septic system drain field were found to be suitable. A satisfactory soil percolation rate of 7.58 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 16 to 33 feet below ground surface. The ground-water flow is to the east or northeast; the gradient could not be calculated. 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 mm/in i n encountered n 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. Water samples were collected from the domestic well on the Site as pa of this investigation. Nitrate was detected in the March 18 sample at a concentration of 11.5 mg/L-N; the MCL for nitrate is 10 mg/L-N. DBCP was not detected in the water sample; the MCL for DBCP is 0.2 ig/L. After several hours of pumping, nitrate was detected in the April 1 and 10 samples at a concentration of 10.5 mg/L-N, just over the4A-G-L- It is recommended for health reasons that bottled water be consumed until the concentration of nitrate can be reduced to below the MCL. The San Joaquin County Environmental Health Department may have recommendations for well deepening or filtration systems to reduce nitrate levels in the drinking water. Based on a review of San Joaquin County Environmental Health Department maps of nitrate and DBCP detections in nearby wells, it appears that no wells within a half-mile radius mile of the Site have been tested for nitrate or DBCP. The Site is located in an agricultural area with few neighbors. 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 of 9.6 mg/L-N for a two-bedroom house, 11.7 mg/L-N for a three-bedroom house, or 13.3 mg/L-N for a four-bedroom house. The three- and four-bedroom scenarios result in a concentration above the US EPA drinking water recommendation of 10 mg/L-N. However, based on the conservative nature of the calculation, distance to any other residential receptors, and clay soil present in the area, it is the professional opinion of Live Oak that septic effluent from a two- or three-bedroom home on the subject Site is unlikely to contribute significantly to a build-up of nitrate in the ground water. Use of a standard, shallow LOGE 1909 Page 14