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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic disposal area for the new ADU on the Site were found to be suitable for a septic system. A satisfactory soil percolation rate of 10.4 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 underlain by clay. Based on maps of recent aquifer levels, the depth of ground water is approximately 55 to 60 feet below ground surface. Ground water flows generally to the northeast in the area at a rate of approximately 15 to 16 feet per mile. A water sample was collected from the domestic well on the Site. Nitrate was detected in the water sample at a concentration of 11.4 mg/L-N, slightly over the MCL of 10 mg/L-N. DBCP was not detected in the water sample. Based on the water test results, it is recommended that bottled water be consumed until the concentration of nitrate in the well water can be brought below the MCL. For the long term, water filtration systems or well modification are options to improve water quality. Additionally, a "Notice to Abate" has been filed for the domestic well on the Site by the San Joaquin County Environmental Health Department due to its open, unsecured condition; Mr. Medina has been contracted to perform the necessary repairs. Based on the methods and assumptions described, the nitrate loading calculation indicates that the existing and proposed future on-site septic drain field systems have the potential to cause a buildup of nitrate in the aquifer up to 12.6 mg/L-N, 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. Ground water is relatively deep in the area and the clay soils may serve to limit the transportation of nitrate to the aquifer. It should be noted again that nitrate levels in the on-site well water already exceed the MCL and that the adjacent mobile home park may be a contributing factor. 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. Future septic system construction should follow the San Joaquin County On-Site Wastewater Treatment Systems Standards (2017) where applicable. In this area, most septic systems utilize leach lines with seepage pits. LOGE 2620 Page 14