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I QUARTERLY MONITORING REPORT APRIL 1997 CANEPA s CAR WASH 248 E Park Street Stoalon CA Apn1 21 1997 generally consistent with previous monitoring results A hydrograph of monitor wells MW-1 through MW-7, presented in Figure 4, Appendix A, Illustrates 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 possibly MTBE were detected in groundwater samples collected during the sampling event Benzene concentrations detected in MW-1, MW-2, MW-3, and MW-5 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 gg/L for MTBE in drinking water, however An unconfirmed MTBE concentration detected in the groundwater sample from MW-5 (180 µg/L) exceeds that level I However, future analysis using EPA Method 8260 may indicate that MTBE is not present in groundwater samples from the site monitoring wells Analytical results for the April, 1997, sampling are generally consistent with historical analytical results TPH-G and BTEX concentrations in the samples from MW-1, MW-2, MW-3, MW- 4, and MW-7, however, are generally at their lowest historical levels 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 in MW-1, MW-2, and MW-3 since groundwater monitoring commenced in September, 1994, and in MW-4, MW-5, MW-6, and MW-7 since the May, 1995, monitoring TPH-G and BTEX concentrations in the sample from MW-5 increased markedly since the August, 1995, monitormg MW-5 is generally down-gradient from the former location of the underground storage tanks TPH-G and BTEX concentrations in the sample from MW-6 are generally unchanged from I previous monitoring results The historical groundwater analytical data for the site are presented in Table A, Appendix B I Floating product was not observed in any of the wells during the April, 1997, quarterly sampling Strong petroleum hydrocarbon odor «as noted in MW-2 and MW-5 I The neat quarterly monitoring event IS scheduled for July, 1997 If you need additional information or have any questions, please contact us at (209) 668-9234 I Respectfully submitted, Condor Earth Technolog %P— GEo`0 011 DONALD F KAESZE 1 Donald F Kresse tp NO 6430 obert J Job, P E California RegisteredCalifornia Registered Geologist #6430 F�F CA4�FOQProfessional Engineer, Civil n51592 ICAN2079 i Page -5- I �� CONDOR