SR0085782_SSNL - Laserfiche WebLink

Home Browse Search

CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic disposal fields on the Site were found to be suitable for standard septic systems utilizing leach lines, leach lines with sumps, or filter beds. Satisfactory soil percolation rates of 2.38 min/in (Parcel 1), 2.08 min/in (Parcel 2), 4.17 min/in (Parcel 3), 3.79 min/in (Parcel 4), 4.63 min/in (Parcel 5), 1.49 min/in (Parcel 6), 5.21 min/in (Parcel 7), 6.41 min/in (Parcel 8), 4.63 min/in (Parcel 9), and 2.19 min/in (Parcel 10) were observed at the test locations. The soils across the Site were found to be mixtures of sand and silt. The depth of ground water based on recent aquifer levels is approximately 38 to 40 feet below ground surface. Ground water flows to the north in the general area at a rate of 1.5 to 2.5 feet per mile. Because of the percolation rates between 1.0 and 5.0 min/in encountered in the test holes on Parcels 1, 2, 3, 4, 5, 6, 9, and 10, 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. Because of the percolation rate between 5.0 and 30.0 min/in encountered in the test holes on Parcels 7, and 8, the San Joaquin County Environmental Health Department will require an 8-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 of 38 to 40 feet, no modification to standard systems up to 8 feet deep should be necessary to comply with this requirement. 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 10.3 mg/L-N, slightly above the MCL of 10 mg/L-N. The analytical results for DBCP were not available by the completion of this report and will be submitted as an addendum. Based on the nitrate level detected, it is recommended that residents of the existing house consume bottled water until the level can be brought below the MCL; in the long term, a water filtration system or well repair can reduce nitrate levels. Based on the methods and assumptions described, the nitrate loading calculation indicates that the use of a proposed septic system from a four-bedroom house on each parcel of the Site has the potential to cause a buildup of nitrate in the aquifer up to 9.1 mg/L-N, below the MCL of 10 mg/L-N. As a result, nitrate mitigation is not recommended at this time. LOGE 2217 Page 15