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t � [41 LOCAL GROUNDWATER AND SURFACE WATER INFORMATION The static water table depth, or the zone of saturation is located at approximately 75 feet below grade according to the 1996 "Lines of Equal Depth" published by the San Joaquin County Flood Control District. It is possible that there may be perched water table conditions under the subject property at a higher elevation that the static water level. This should be investigated at the time of seepage pit installation. If perched conditions are encountered, our firm should be notified to assess the situation. It may be determined that the pits must remain five feet above this perched water, or that sumps may have to be installed. There is no potential for septic impact to any surface waters, providing applicable distance requirements are followed. , I �� 1nA Analysis of water drawn from the irrigation well which serves the subject vineyard and orchard, I" reveals a nitrate concentration of 66 ppm NO3. The Maximum Contaminant Level (MCL) for NO3 D( in drinking water is 45 ppm. The pesticide DBCP was detected at 0.68 �g/L or 0.00068 mg/L. The v MCL for DBCP is 0.0002 mg/L. The pesticide EDB was not detected(ND). Considering the intense ��p agricultural production in this part of the County, a high nitrate concentration was to be expected �b I from the well water analysis. This also applies to the pesticide DBCP, which was used extensively ML in vineyards until 1979. [51 CONCLUSIONS The acceptable percolation rates obtained for the subject parcels suggest there would be effluent percolation at the shallower depths of approximately 42-48 inches below grade. As referenced earlier, there are no plans to build on any of the six parcels, except the parcel located in the southeast corner of the subject site. We are recommending that seepage pits be installed if any development is to take place on the subject site. The leachfield(s) should consist of 12,000 square feet. This leachfield square footage area will be largely dependent upon the number of bedrooms a proposed house will have, and may be reduced for a smaller house. However, if there will be several people inhabiting the residence, particularly children, a septic system should be oversized to accommodate additional wastewater flows. A 50% standby replacement area must also be incorporated into the design of any septic system. All related septic system structures and domestic well(s) must comply with the published "distance" requirements from property borders, roads, irrigation fields, etc. The referenced leachfield area will help ensure stability and guard against leachfield failure. A failure would primarily result from the advanced formation of a "biomat" or "clogging mat" on the wetted soil/effluent interface. This mat is composed mostly of aerobic and anaerobic bacteria and bacterial products consisting of a slime of polyuronides and polysaccharides. If the soil/effluent interface is well aerated, a variety of soil microfauna such as nematodes and protozoa may digest the clogging mat bacteria. Since the subsurface soils consist of a heavier clay material, anaerobic conditions will probably prevail which may hasten leachfield failure. In this scenario, the seepage pits then manage most of the effluent, although seepage pits can also develop biomat formation and lead to complete failure of the septic sstem. 0;> *-hty (?ontrol Inspection