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151 LOCAL GROUNDWATER AND SURFACE WATER INFORMATION .. A boring was drilled by hand to determine the static groundwater depth under the subject property. The capillary fringe was encountered at 8.0 feet. The boring was extended to 8.9 feet. Static water level is under pressure and rose to 7.3 feet. The final depth of boring was 8.9 feet. This boring was backfilled with neat bentonite clay to form a basal plug for groundwater protection. Maps published by the Flood Control District do not indicate the groundwater depth. There was no evidence of a perched water table condition during our exploratory boring procedures. As referenced, the project is near the Tom Paine Slough and it is our understanding the project is considered to be in the flood zone. A water sample was taken for analysis of nitrate from the deep boring to determine groundwater depth. The attached analysis reveals a comparatively low level of 18 ppm of nitrate in the top groundwater aquifer. This indicates there has apparently been little impact from agricultural operations in the area. It is our opinion there is no potential impact from the proposed septic system am Ito surface waters, namely the Tom Paine Slough. 161 CONCLUSIONS The failure of the percolation test indicates a filter bed septic system with a 1,000 square foot leaching area will have to be constructed. Sumps cannot be used in this area due to the high groundwater table. A 1600 gallon Zabel filter septic tank must also be installed. It is important the filter bed area be constructed carefully. Approximately 18 inches of soil must be removed in this 1000 square foot area. The backhoe must not encroach upon the excavation area to prevent compaction of the clay soil and to allow the natural cracking of the soil to remain. After the installation of the piping network, engineered backfill material must be used over this piping network. The engineered fill must be granular in nature with a small percentage of fines to allow capillary action and surface evaporation of the effluent. The filter bed area must be at grade level, but be able to be protected from flood inundation. Additionally, the origin of the septic effluent from the "Coach" must be at the prescribed elevation. At least a 100% standby replacement area must also be incorporated into the filter bed design. Although this is the best septic system design for this location, there still remains the possibility for system failure. It is our understanding there is to be eventually five employees; consequently, additional filter bed area must be designated. Additionally, low flow toilets and sinks must also be installed. t� ` *ality (9-trol I"spm tion