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QUARTERLY MONITORING REPORT APRIL 1997 16CANEPA S CAR WASH 6230 Pacific Avenue Stockton CA April 17 1997 ' Appendix A) indicates groundwater mounding in the center of the site around MW-1 and MW-2 This is generally consistent with previous monitoring results Attempts have been made by previous ' consultants to explain this apparent local recharge with a potentially leaky sewer line Hydrographs of monitor wells MW-1 through MW-8, presented in Figure 4, Appendix A, illustrate the fluctuation of the groundwater table Historical groundwater measurements are provided in the accompanying Hydrograph Table The results of the laboratory analyses Indicate that TPH-G, BTEX, and MTBE were detected ' in groundwater samples collected during the sampling event Benzene concentrations detected in MW- 1, MW-2, and SV-9 exceed the maximum contaminant level (MCL) for benzene (1 0 µg/L) in drinking water (California Code of Regulations, Title 22, Drinking Water Regulatory Criteria) No ' MCL has yet been established for MTBE The California Department of Health Services has set an action level of 35 p.g/L for MTBE in drinking water, however MTBE concentrations detected in groundwater samples from MW-1, MW-2, and SV-9 exceed that level ' Analytical results for the April, 1997, sampling are generally consistent with historical analytical results TPH-G, BTEX, and MTBE concentrations in the samples from MW-1 and MW-2, ' however, are generally at their lowest historical levels In addition, the sample from MW-7 did not contain either TPH-G or BTEX constituents for the first time in its history Most of the other monitor wells have generally experienced a decline in TPH-G and BTEX concentrations relative to 1994 and 1995 results This cannot necessarily be attributed to natural attenuation because the water level in the wells has been above or very near the top of the well screens during the August and October, 1996, and January and April 1997, monitoring The historical groundwater analytical data for the site are presented in Table A Appendi\ B IFloating product was not observed in any of the wells during the April, 1997, quarterly sampling Slight petroleum hydrocarbon odor was noted in MW-1 and SV-9 Floating product has not been reported in previous groundwater monitoring from June, 1994, through January, 1997 The next quarterly monitoring event is scheduled for July, 1997 If you need additional information or have any questions, please contact us at (209) 668-9234 Respectfully submi BRED GEDZ Condor Earth Te i Off, -A DONALD F KREu�'- - ... NO 6430 �' i d ' Donald F Kres �'>, Robert J Sob, P E I California Regist �' 2`� California Registered Geologist #6434 fOF CAI- Professional Engineer Civil #51592 CA\2QT 97 IPage -5- I �d CONDOR