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i` L , i (§ 4.0) LOCAL GROUNDWATER AND SURFACE WATER INFORMATION 4.1 The 1999 Lines o Equal Depth Ma published b the San Joaquin Count Flood Control � {§ ) ,f q P p p Y q Y illustrates the groundwater depth to be 122 feet below ground surface (b.g.s.). The 1999 Lines of Equal Elevation Map illustrates the groundwater elevation and the directional flow to be in a west, southwesterly direction. Unfortunately, no Well Driller's Log exists for the on-site domestic well. Consequently, underground lithology specific to the subject property cannot be discerned. The property is not subject to 100-year flooding. Therefore, it is highly unlikely there would be surfacing of effluent from inundated conditions. Surface water will be managed by on-site retention basins. (§ 4.3,4.4 and 4.5) A water sample was obtained from a hose bibb next to the pressure tank of the Welch's domestic well after the well was allowed to cycle three times to ensure the sampling of aquifer formation water. (§ 4.6) The sample was placed in a cooled ice chest and transported under the attached Chain of Custody to A&L Labs in Modesto, California to be analyzed for f nitrate and DBCPIEDB. Water analysis reveals a low nitrate concentration of 9 ppm. The Maximum Contaminant Level (MCL) for NO, in drinking water is 45 ppm. This 9 ppm concentration may be considered a background concentration that has accumulated over eons and can be attributed to the deep groundwater, high clay content intervening strata, very low septic system density and no intense (fertilized) agriculture surrounding the property(until recently). i (§ 7.0) CONCLUSIONS The perc test results for proposed Parcels 1, 2, 3 and 4 show acceptable percolation for the management of septic system effluent flows. For Parcels 1 and 2, effluent management will occur at the deeper depths representative of sumps, and not necessarily under the leachlines. For Parcels 3 and 4, effluent management will mostly occur at the shallow leachline depths and only marginally in k the deeper sump depths. Although the deep perc tests for Parcels 3 and 4 were run at simulated sump depths due to the encountered material which was the most favorable material at the highest elevations, seepage pits should be installed on these two Parcels. Seepage pits will give the highest capacity(volume) for effluent management. As noted for the shallow tests on Parcels 1 and 2, there will be some effluent percolation at leachline depth, but if the soil becomes saturated, percolation will cease and the sumps will manage effluent flows. A new law that is to be implemented may restrict the installation of seepage pits (Assembly Bill 885). Before this law is implemented, EHD may require the installation of seepage pits on Parcels 1 (for a second unit dwelling), 2, 3 and 4 of this project for a number of reasons: 1.) They are the typical and principle effluent management structure installed in this area, 2.) There is a significant distance of approximately 100 feet between the bottom of a seepage pit at 25 feet b.g.s. and the current groundwater depth of 122 feet, 3.) Seepage pits allow head pressure buildup to force effluent into Page -4- Chesney Consulting I