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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic leach field area for the new ADU on the Site were found to be suitable for a septic system. A satisfactory soil percolation rate of 6.94 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. Based on maps of recent aquifer levels, the depth of ground water beneath the Site is approximately 15 to 20 feet below ground surface. Ground water flows generally to the northeast in the area; the flow rate for the Site could not be calculated due to its position beyond the mapped contours. Because of the percolation rate between 5.0 and 30.0 min/in encountered in the test hole, the San Joaquin County Environmental Health Department will require an 8-foot separation from the bottom of the dispersal system to ground water, unless mitigated by system design or enhancement. Given the estimated depth to water, no modification to a shallow leach line or filter bed septic system should be necessary to comply with this requirement. A water sample was collected from the domestic well on the Site. Nitrate was detected in the water sample at a concentration of 12.7 mg/L-N, over the MCL of 10 mg/L-N. DBCP was not detected in the sample. Based on the water test result, it is recommended that bottled water be consumed until the concentration of nitrate in the well water can be brought below the MCL. According to permit records, the well has a relatively shallow (50-foot) grout seal depth. For the long term, water filtration systems or well modification are options to improve water quality. Based on the methods and assumptions described, the nitrate loading calculation indicates that existing and future septic system use on the Site has the potential to cause a buildup of nitrate in the aquifer up to 11.3 mg/L-N, slightly over 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 clay soil can mitigate nitrate migration. Current nitrate levels in the domestic well exceed the predicted result. Although Live Oak cannot make engineering recommendations, we are aware that the San Joaquin County Environmental Health Department often allows the use of standard septic systems with oversized septic tanks in cases where a 30 percent reduction would bring the nitrate loading under the MCL; the subject Site's nitrate loading result meets this criterion. Any future septic system construction should follow the San Joaquin County On-Site Wastewater Treatment Systems Standards (2017) where applicable. In this area, only shallow septic systems (leach lines or filter beds) are permitted. LOGE 2637 Page 15