SR0080832 - 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. A satisfactory soil percolation rate of 15.62 min/in was observed in the shallow soil zone at the test location. The depth of ground water based on recent aquifer levels is estimated to be 37 to 45 feet below ground surface. The ground-water flow beneath the Site is to the north or north-northeast at a rate of approximately four feet per mile. San Joaquin County experienced its highest recent ground-water levels in 1983 and 1999; depth to water beneath the Site was approximately 18 to 23 feet during spring of these years. 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, or mitigation by system design or enhancement. Based on the predicted depth to water, no modification to standard, shallow systems should be required. A water sample was collected from the irrigation well on the Site as partof this investigation. Nitrate was detected in the sample at a concentration of 12.3 mg/L-N, slightly above the MCL of 10 mg/L-N. DBCP was not detected in the sample; the MCL b for DBCP is 0.2 ug/L. When the new domestic well has been drilled, it should be tested for nitrate. If nitrate levels in the domestic well exceed the MCL, it is recommended for health reasons that bottled water be consumed until the concentration of nitrate can be V reduced to below the MCL. The San Joaquin County Environmental Health Department \_ may have additional recommendations to reduce nitrate levels in the drinking water. �1 The Site and the surrounding agricultural properties are mainly orchards; elevated nitrate levels in the area likely derive from fertilizer application on these properties. Based on a review of the San Joaquin County Environmental Health Department's map of nitrate detections in nearby wells, five wells within a one-mile radius of the subject Site have been tested. Nitrate was detected in two of the wells at concentrations between 0.1 and 5.0 mg/L-N, and in three of the wells at concentrations between 5.1 and 10 mg/L-N. Three wells within a one-mile radius of the Site were tested for DBCP. No DBCP was detected in two of the wells; it was detected in the third well at a concentration over 0.2 ug/L. Based on the current 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 1.6 mg/L-N. This level falls below the US EPA drinking water recommendation of 10 mg/L-N. LOGE 1932 Page 13