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CONCLUSIONS AND RECOMMENDATIONS In summary, the shallow soil conditions examined near the proposed septic system drain field appear to be suitable. A satisfactory soil percolation rate of 2.1 minutes per inch was observed for the shallow percolation test. The depth of ground water based on recent aquifer levels is approximately 30 to 44 feet below the ground surface, depending on the season. The ground-water flow direction could not be determined in the vicinity of the Site. The on-site irrigation water well (planned for future winery use) was tested once for nitrate and twice for DBCP. Nitrate was detected at a concentration of 1.4 mg/L-N in the water sample, well below the US EPA's Maximum Contaminant Level (MCL) of 10 mg/L-N. DBCP was detected in both samples at concentrations of 0.25 and 0.28 µg/L, slightly above the MCL of 0.2 ug/L. For health reasons, we recommend that well water not be consumed until DBCP levels can be reduced to below the MCL. Use of water filters or deepening the well could potentially improve the water quality. Utilizing bottled water for drinking also may be a good alternative to consider. The San Joaquin County Environmental Health Department may be able to provide additional suggestions. Based on the existing residence and proposed project, the use of on-site septic tanks and drain field systems on the Site is not expected to cause a buildup of nitrate in the aquifer above 1.2 mg/L-N. This level falls well below the US EPA drinking water recommendation of 10 mg/L-N. We believe the Site suitable for the use of septic systems utilizing leach lines, leach lines and shallow sumps, or a filter bed. As discussed in the On-Site Wastewater Treatment Systems Standards (2017), a percolation rate of greater than 1 min/in but less than 5 min/in requires 20 feet separation from the bottom of the septic system to ground water; the estimated depth to water in the area of the Site is 30 to 45 feet. Based on the satisfactory result of the nitrate loading calculation, no nitrate mitigation is recommended. LOGE 1841 Page 14