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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 septic system. A satisfactory soil percolation rate of 7.8 min/in was observed in the shallow soil zone at the test location. The soil in the test location was found to be silty clay with sand. The depth of ground water based on recent aquifer levels is approximately 88 to 92 feet below ground surface. Ground water flows to the north in the area at a rate of approximately 7 to 11 feet per mile. 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 7.5 mg/L-N, below the MCL of 10 mg/L-N. DBCP was not detected in the sample. 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 15.4 mg/L, which exceeds the MCL of 10 mg/L-N. It should be remembered that 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. The clay soil and deep ground water in the area may serve to limit the transportation of nitrate to the aquifer. Indeed, the nitrate level in the on-site well was found to be only 7.5 mg/L-N, despite the existing house and substantial residential development in the area. Septic system construction should follow the San Joaquin County On -Site Wastewater Treatment Systems Standards (2017) where applicable. It is recommended that the new system utilize only leach lines or a filter bed rather than deep seepage pits; this recommendation is intended to provide additional protection to ground water. Recent San Joaquin County Environmental Health Department policy has been to evaluate each project on a case-by-case basis to determine whether nitrate mitigation is warranted. Although Live Oak cannot make engineering recommendations, we are aware that in the past the San Joaquin County Environmental Health Department has allowed the use of an oversized septic tank combined with soil amendments in the shallow leach field area to mitigate nitrate impacts; this option may be worth exploring for the Site. As an alternative if space is tight, a septic system engineered to reduce nitrate could be utilized with deep seepage pits. LOGE 2204 Page 15