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CONCLUSIONS AND RECOMMENDATIONS <br />In summary, the soil conditions examined near the proposed septic system drain field <br />were found to be suitable for a septic system utilizing leach lines or a filter bed. A <br />satisfactory soil percolation rate of 6.25 min/in was observed in the shallow soil zone at <br />the test location. The soil in the test location was found to silty sand; much of the soil <br />across the Site has been disturbed due to past environmental remediation activities. <br />Because of the percolation rate between 5.0 and 30.0 min/in encountered in the test <br />hole, the San Joaquin County Environmental Health Department will require an 8-foot <br />separation from the bottom of the dispersal system to ground water at that location, <br />unless mitigated by system design or enhancement. <br />The depth of ground water beneath the Site is reported to fluctuate from 8.6 to 16.5 feet <br />below ground surface. The ground-water flow direction is reportedly to the north- <br />northeast beneath the Site. <br />No water sample was collected as part of this investigation. No wells are located on the <br />Site, which will eventually connect to the municipal water system. Based on maps <br />reviewed, neither nitrate nor DBCP appears to be a problem in nearby wells. <br />The Site is the location of a closed leaking underground storage tank case, and some <br />subsurface contamination may remain; detailed investigation and discussion of this <br />issue are beyond the scope of this report. The developer may wish to contact the San <br />Joaquin County Environmental Health Department prior to construction to discuss <br />recommendations. <br />Based on the methods and assumptions described, the nitrate loading calculation <br />indicates that the use of an on-site septic tank and drain field system on the Site has the <br />potential to cause a buildup of nitrate in the aquifer up to 7.6 mg/L, below the maximum <br />drinking water standard of 10 mg/L-N. <br />Septic system construction should follow the San Joaquin County On-Site Wastewater <br />Treatment Systems Standards (2017) where applicable. Because of the favorable <br />result of the nitrate loading calculation, no nitrate mitigation is recommended at this <br />time. <br />LOGE 2130 Page 13