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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 system utilizing leach lines or a filter bed. A satisfactory soil percolation rate of 11.9 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 nine to 20 feet below ground surface, depending on the season. The ground-water flow beneath the Site is predominantly toward the northwest at a rate of approximately seven to eight feet per mile in the vicinity of the Site. Depth-to-water data were not available for the vicinity of the Site during the 1983 and 1999 high-water seasons. Because the percolation rate encountered falls between 5.0 and 30.0 min/in, 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 water beneath the Site, a mounded system may be required. The San Joaquin County Environmental Health Department and/or the septic contractor should provide specifications for the system, if needed. 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 28.3 mg/L-N, significantly 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 the opinion of Live Oak that the nitrate level detected in the water sample likely reflects the relatively shallow (50') grout seal on the domestic well, rather than a localized high nitrate concentration; this part of Tracy is known to have high nitrate levels in shallow ground water, largely due to agricultural activities. For health reasons, it is recommended 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 on a long-term basis. Based on the method and assumptions described, the use of on-site septic tanks and drain field systems on the Site should not cause a buildup of nitrate in the aquifer above the US EPA drinking water recommendation of 10 mg/L-N. The maximum build-up of nitrate from the use of septic systems on the Site is predicted to be 3.3 mg/L-N. Because of the favorable result of the nitrate loading calculation, no nitrate mitigation is recommended for the proposed new septic system. LOGE 1843 Page 14