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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 1.77 min/in was observed in the shallow soil zone at the test location. The soil in the test location was found to be fine sandy silt. The depth of ground water based on recent aquifer levels is approximately 19 feet below ground surface. The general ground -water flow direction in the area is to the northeast. Because of the percolation rate between 1.0 and 5.0 min/in encountered in the test hole, the San Joaquin County Environmental Health Department will require a 20 -foot separation from the bottom of the dispersal system to ground water, unless mitigated by system design or enhancement. 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 6.3 mg/L-N, well below the MCL of 10 mg/L-N. DBCP was detected in the sample at a concentration of 0.010 ug/L, well below the MCL of 0.2 ug/L but above the MCLG of zero. 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 16.3 mg/L. 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. Indeed, the two homes have been located on the Site for many years, yet the nitrate level in the on-site well was found to be only 6.3 mg/L-N. Four of five nearby wells similarly have not .exhibited nitrate exceedance, despite relatively dense residential and commercial/industrial development in the area. Septic system construction utilizing leach lines or a filter bed should follow the San Joaquin County On -Site Wastewater Treatment Systems Standards (2017) where applicable. 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 leach field area to mitigate nitrate impacts; this option may be worth exploring for the Site. LOGE 2154 Page 13