SR0080668 SSNL - Laserfiche WebLink

Home Browse Search

CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic system drain field were found to be suitable for a septic system utilizing leach lines and seepage pits. A satisfactory soil percolation rate of 10.0 min/in was observed in the shallow soil zone at the test location. The depth of ground water based on recent aquifer levels is approximately 83 to 93 feet below ground surface. Ground water flows down to the northeast at a rate of approximately eight feet per mile. The highest recent ground-water levels for the area were experienced in spring of 1983 and 1999; at these times, ground water would have been present at approximately 72 to 78 feet below ground surface. Because the percolation rate encountered falls between 5.0 and 30 min/in, the San Joaquin County Environmental Health Department will require an eight-foot separation from the bottom of the dispersal system to ground water. Based on depth to water in the area, no modifications to standard systems should be required. 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 6.4 mg/L-N, well below the MCL of 10 mg/L-N. DBCP was not detected. Based on a review of San Joaquin County Environmental Health Department maps of nitrate and DBCP detections in nearby wells, 11 wells within a half-mile radius of the subject Site have been tested for nitrate. Nitrate was detected in eight of these wells at concentrations between 0.1 and 5.0 mg/L-N, in two of the wells at a concentration between 5.1 and 10 mg/L-N, and in the last well at a concentration over 10 mg/L-N. Eight wells within a half-mile radius of the Site have been tested for DBCP; it was not detected in any of the wells. Based on the current project, the maximum buildup of nitrates in the aquifer from the use of septic systems on the Site is predicted to be 12.6 mg/L-N. The result of the nitrate loading estimate exceeds the maximum drinking water standard. However, based on the conservative nature of the calculation, depth to water beneath the Site, clay soil present in the area, and lack of existing nitrate problem in the area, it is the professional opinion of Live Oak that septic effluent from the subject Site is unlikely to contribute substantially to a build-up of nitrate in the ground water. The use of a standard septic system should be allowed for the current development. LOGE 1920 Page 13