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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic disposal area for the garage conversion ADU on the Site were found to be suitable for a septic system. A satisfactory soil percolation rate of 1.54 min/in was observed in the shallow soil zone at the test location. The soil in the test location was found to be silty sand. Based on maps of recent aquifer levels, the depth of ground water is approximately 58 feet below ground surface. Ground water flows generally to the northwest in the area at a rate of approximately 3.5 feet per mile. 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. Given the estimated depth to water, no modification to the proposed septic system should be necessary to comply with this requirement. Live Oak collected a water sample from the domestic well on the Site on April 9, 2026. Nitrate was detected in the water sample at a concentration of 18.8 mg/L-N, significantly over the MCL of 10 mg/L-N. DBCP was detected in the sample at a concentration of 0.09 µg/L, under the MCL of 0.2 µg/L but over the MCLG of zero. 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. Although the DBCP level is below the MCL, the owner may wish to investigate options to reduce this constituent as well; because DBCP is a volatile chemical, a point-of-entry filtration system would be preferable to a single-faucet filter. 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 12.1 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. Ground water is relatively deep in the area, and only shallow septic systems are permitted in this part of the County; consequently, the system will have a substantial vadose zone. Selection of leach lines or a filter bed septic system, rather than leach lines with sumps, would increase this separation. It should be noted again that nitrate levels in the on-site well water already exceed the MCL and that fertilization of the surrounding orchards 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 LOGE 2619 Page 15