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" comparison to the low density housing and indicates the shallow soils in the area are not conducive to acceptable management of sewage effluent over long periods of time. This is primarily attributed to the tight, silty soils at the leachline depth. [3] SOIL PROFILE AND PERCOLATION TESTING One shallow percolation test was conducted on Parcel 1 according to San Joaquin County Department of Environmental Health regulations. No perc test was performed on the Designated Remainder per Department regulations. The perc test location is illustrated on the attached Parcel Map. Percolation test results can be found on the Field Test Data Sheet in the Appendix. Perc test results indicate a comparatively fast percolation after the four hour test period. Soil structures consists of a tight sandy silt (SM) throughout the shallow soil profile. No hardpan _ layer was encountered. The boring was pre-saturated the total depth, 24 hrs prior to starting the perc test to induce worst-case saturated soil conditions. Percolation test results indicate a perc rate of 7.1 min/in for Parcel 1. Considering the soil type, this rate can be considered favorable. It is our opinion that the material at the test depth of 42 inches is of sufficient porosity to allow water infiltration and percolation. However, repeated saturations from septic effluent in conjunction with the propensity of the soil to build up a biomat, leads to leachline failures as evidenced by the repairs. [4] LOCAL GROUNDWATER AND SURFACE WATER INFORMATION The static water table depth, or the zone of saturation is located at approximately 55 feet below grade from the sounding of a domestic well on Ohm Road. The 1996 "Lines of Equal Depth" published by " the San Joaquin County Flood Control District does not reference the static water table depths in this area. It is possible there may be perched water table conditions under the subject property at a higher elevation than the static water level and this should be investigated if seepage pits are ever installed. There is no potential for septic impact to any surface waters, providing applicable distance requirements are followed. The property is not in the flood plain. Analysis of water drawn from the domestic well at the farm labor residences near the intersection of Ohm Road and Koster Road indicates a nitrate concentration of 22 ppm NO3. The Maximum Contaminant Level (MCL) for NO3 in drinking water is 45 ppm. The pesticides DBCP and EDB were not detected(ND). A nitrate concentration of 22 ppm indicates the underlying shallow aquifers have been moderately impacted from nitrogen contributors, such as agricultural operations, septic systems or rainfall. No well logs were available in the area to verify if clay layers may have helped attenuate the downward migration of nitrate molecules. 2