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CONCLUSIONS AND RECOMMENDATIONS <br /> In summary, the soil conditions examined near the existing septic system drain field <br /> were found to be suitable. <br /> A satisfactory soil percolation rate of 5.43 min/in was observed at the test location. The <br /> soils in the test location were found to be silty clay to 1.5 feet below ground surface, <br /> followed by sandy silt with clay to 3.0 feet, followed by silty sand to the full depth of the <br /> hole. The percolation test is considered representative of soils within a 100-foot radius <br /> of the test location. <br /> Ground-water depth and flow direction in the Delta islands is highly dependent on <br /> seasonal pumping and irrigation in the area. Based on maps reviewed and projection of <br /> mapped ground-water contours, depth to ground water beneath the Site is anticipated to <br /> be less than 15 feet. <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 eight- <br /> foot separation from the bottom of future dispersal systems to ground water. <br /> A water sample was collected from the domestic well on the Site. Neither nitrate nor <br /> DBCP was detected in the sample. <br /> Based on the methods and assumptions described, the nitrate loading calculation <br /> indicates that the use of on-site septic tanks and drain field systems on the Site has the <br /> potential to cause a buildup of nitrate in the aquifer up to 3.2 mg/L, well below the MCL <br /> of 10 mg/L-N. As a result, no nitrate mitigation is recommended. <br /> LOGE 20-17 Page 13 <br />