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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic disposal field(s) on the Site were found to be suitable for septic systems utilizing leach lines or filter beds. A satisfactory soil percolation rate of 2.0 min/in was observed at the test location. The soil in the test location was found to be sandy silt. The depth of ground water based on recent aquifer levels is approximately 26 to 27 feet below ground surface. Ground water appears to flow to the north in the general area; the gradient could not be calculated. 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, it is recommended that only shallow systems (leach lines or filter bed) be installed at this test location. A water sample was collected from the domestic well on the Site as part of this investigation. Nitrate was detected in the sample at a concentration of 19.4 mg/L-N, substantially above the MCL of 10 mg/L-N. DBCP was not detected in the sample. Ms. Tijero is aware that nitrate levels at the Site exceed the MCL and is utilizing a filter to remove nitrate from the domestic water. At her request, a second sample was collected from the spigot left of the garage door, which is connected to the water supply after filtration. In this sample, nitrate was detected at a concentration of 2.9 mg/L, well below the MCL. It is recommended that all future residential construction employ similar water filtration systems. Based on the methods and assumptions described, the nitrate loading calculation indicates that the use of existing and proposed septic tanks and drain field systems on the Site has the potential to cause a buildup of nitrate in the aquifer up to 10.7 mg/L-N (two homes) or 12.7 mg/L-N (two homes plus ADU), both slightly above the maximum drinking water standard of 10 mg/L-N. It should be remembered that the Hantzsche and Finnemore equation is a conservative method for determining potential impacts, and actual nitrate loading experienced on the Site over time may be less than predicted. Although Live Oak cannot make engineering recommendations, we are aware that the San Joaquin County Environmental Health Department often allows the use of standard 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. The use of shallow septic leach fields rather than deeper sumps is anticipated to provide additional reduction in nitrate loading. LOGE 2234 Page 14