SR0085445_SSNL - Laserfiche WebLink

Home Browse Search

CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic disposal field on the Site were found to be suitable for a standard septic system utilizing leach lines with seepage pits. A satisfactory soil percolation rate of 11.9 min/in was observed at the test location. The soils in the test location were found to be clay, sandy clay, and sandy silt. The depth of ground water based on recent aquifer levels is approximately 116 to 146 feet below ground surface. Ground water appears to flow to the northwest or south in the general area, at a rate of approximately five to ten feet per mile, depending on the season. 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 1.4 mg/L-N, well below the MCL of 10 mg/L-N. DBCP was not detected in the sample. 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 14.2 mg/L-N, 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. The clay soil and deep ground water in the area may serve to limit the transportation of nitrate to the aquifer. Indeed, the nitrate level in the on-site well was found to be only 1.4 mg/L-N, despite the existing house and substantial residential development in the area. Additionally, Live Oak and Mr. Matthews met with Mr. Shih, Program Coordinator for Land Use at the San Joaquin County Environmental Health Department on April 25, 2022. At this time, Mr. Shih indicated that the use of an oversized (2,000 -gallon) septic tank at the second unit dwelling would be sufficient to mitigate nitrate impacts at the Site due to an anticipated 30 percent nitrate reduction in the effluent from the larger tank. Mr. Matthews intends to reuse the existing leach field, which has been tested by River Rats Septic & Plumbing Services and found to be functional. The combination of the larger tank and the existing leach field should provide a practical solution for the septic needs of this existing small residence. LOGE 2226 Page 14