SR0085175_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, sumps, or deep trenches. A satisfactory soil percolation rate of 13.9 min/in was observed in the deep soil zone at the test location. The soil strata at the test location were found to include silts, sands, and clays. The depth of ground water based on recent aquifer levels is approximately 60 to 62 feet below ground surface. The ground -water flow is to the southeast at a rate of approximately 5 to 6 feet per mile. Environmental Enterprises, Inc. provided Live Oak with April 2020 test results for the two new public wells on the Site, Well #3 (new north) and Well #4 (new south). Neither nitrate nor DBCP was detected in either sample. The older, shallower wells on the Site (now destroyed) were reported to contain both constituents, as well as 1,2,3 -TCP. A water filtration system was installed to improve water quality; the system remains in place despite the significantly improved water quality from the new wells. Utilizing the methods and assumptions described, the nitrate loading calculation indicates that the use of an on-site septic tank and drain field system on the Site has the potential to cause a buildup of nitrate in the aquifer up to 12.4 mg/L, slightly over the MCL of 10 mg/L-N. This scenario assumes a standard septic system without treatment. We understand, however, that the existing advanced treatment system was designed to mitigate nitrate and that nitrate monitoring is performed and reported quarterly to the California Regional Water Quality Control Board. Results from 2020 through 2022 suggest that the treatment system is extremely effective at removing nitrate from the effluent, often reducing it to a level below the detection limit. As a result, actual nitrate loading experienced on the Site should fall well below the predicted value as long as the advanced treatment system is operating according to design and consistent with the reported results. LOGE 2218 Page 15