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FDistrict L GROUNDWATER AND SURFACE WATER INFORMATION nes ofEgual Elevation Map published by the San Joaquin County Flood Control e only recent groundwater map available that illustrates the groundwater elevation in this area. This map illustrates the groundwater directional flow to be in a northward direction toward the San Joaquin River. A hand-boring was drilled near the location of the leachfield that will serve the single family residence on Parcel 2. The phreatic zone or zone of saturation was encountered at 8 ft below grade. After 24 hr stabilization the groundwater rose to 7 ft below existing grade, indicating confined conditions at the top of the water table. The boring was backfilled with a bentonite plug. This groundwater depth correlates with a study completed early in the year 2000 directly on the northwest side of Interstate 5 and Kasson Road at the cardlock fuel company, where the water table depth was also determined to be 8 ft below existing grade. Perched water table conditions cannot exist at higher elevations than the static water table since the water table elevation is shallow. There is no potential for future septic impact to surface waters, provided applicable distance requirements are followed, and there is no surfacing of effluent from inundated conditions caused by over-irrigation of the surrounding cropland. Analysis of water drawn from the on-site domestic well (denoted as "proposed new well" on the Tentative Map)reveals a comparatively high nitrate concentration at 40 ppm nitrate (as NO3). The Maximum Contaminant Level (MCL) for NO3 in drinking water is 45 ppm. The construction details of this domestic well are unknown. Agricultural production to the south(upgradient)has most likely contributed to this high nitrate level. The agrichemicals DBCP and EDB were below detection limits (BDL)which is equivalent to non-detect(ND). CONCLUSIONS The perc test results for Parcel I and Parcel 2 suggests there will be effluent percolation at the maximum leachline depth of 42 inches. Water table depth determination reveals that the leachlines must adhere to the five-foot separation distance rule in which the bottom of the leachline trench must be five feet above the static ground water table. This allows for the "treatment" of septic effluent before it encounters the groundwater table. Depending on the final floor elevations of the office and residential buildings, it may be a possibility that the effluent will have to be pumped to higher elevation leachlines that are 1.5 to 2 feet below final grade. Additionally, filters should be used in the second compartment of the septic tanks, or if pumps arc needed,the use of filter vaults. As noted on the Leachline Requirement Map published by the Environmental Health Department, the subject property is in the "High Water Table Areas." The map shows that seepage pits are not allowed in this area and there must be 100 feet of leachline for each bedroom in the residential Page -3- Valky Ag Research