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File No. 20--2921-01 KLEINFELDER <br /> March 25, 1992 <br /> precipitation was found to be approximately 5.4 mg/l. In <br /> order to evaluate whether this figure would impact the <br /> existing groundwater conditions in the study area, it was <br /> then important to determine the initial or background nitrate <br /> concentration in the groundwater. In this regard, we <br /> collected water samples for nitrate content testing from the <br /> domestic wells of the four residences visited off Foppiano <br /> Lane and Canepa Road. The results are presented in the <br /> following table, and the laboratory test result sheets are <br /> included with this report. <br /> NITRATE CONTENT TESTS <br /> Test Results <br /> Location Date Sampled _ (mg/l)______ <br /> 6257 Foppiano 3-3-92 62 <br /> 8721 Canepa 3-3-92 <1 <br /> 6197 Foppiano 3-9-92 39 <br /> 6081 Foppiano 3-9--92 18 <br /> *7065 Foppiano 10-1-91 14 <br /> *Tested for previous study northeast of site <br /> After discussing these results with San Joaquin County <br /> Environmental Health personnel, it was decided to eliminate <br /> the high and low values and average the remaining tests. It <br /> is the County's and our feeling that the high result was <br /> likely because of farming activity around the well location <br /> and possibly inadequate construction/sealing of the. well. <br /> Following the above criteria, we estimate an average <br /> background nitrate concentration of 25 to 30 mg/l beneath the ! <br /> site. Using the higher background value of 30 mg/l and the <br /> calculated Nc of 5.4 mg/l, it can be seen that the resultant <br /> nitrate concentration is still less than the State limit of <br /> 45 mg/1: Based onthis analysis, it is our opinion that the I <br /> proposed sdRrd _cion currently under consideration, with a <br /> maximum_slenB ty of QI1e,-unit r�_acre. -is not likely to <br /> increase the nitrate concentration in the upper _aSHifer <br /> beyond a State imp o <br /> i <br /> We note that our conclusion is based on both measured and <br /> assumed values. In our review of references 1 through 4, it <br /> is clear that the techniques used to evaluate the effect of <br /> septic tanks on the nitrate level in groundwater is very much <br /> an art rather than a science. In addition, the "Hantzche" <br /> mass balance equation used by the CRWQCB does not take into <br /> account all of the factors connected with the impact of <br /> Copyright 1992 Kleinfelder, Inc. Page 7 of 9 <br />