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"1 *' Second Quarter,2003 Quarterly Groundwater Monitoring Report Canepa s Car Wash,Pacific Avenue,Stockton,CA Page 3 groundwater elevations is attached as Figure 3 It should be noted that well screens for shallow monitor . wells MW-1 through MW-7 were drowned Table 2 Groundwater Elevation Data (April 17, 2003) Well Casing Well Collar Depth to Groundwater Screen WELL Elevation Water Elevation Interval (feet) (feet) (feet) feet-b s MW-1 50-70 1548 3561 -20 13 MW-2 50-70 1529 35 17 -1988 MW-3 50-70 1553 36 13 -2060 MW-4 50-70 15 83 3648 -2065 MW-5 50-70 1471 3561 -2090 MW-6 45-65 1489 3455 -1966 MW-7 45-65 15 80 3552 -1972 MW-9 25-45 1484 3566 -2082 L -to 25-45 1472 3469 -1997 MW-11 25-45 15 12 3494 -1982 MW-12D 100-110 1 1499 3480 -1981 LABORATORY ANALYTICAL RESULTS The groundwater samples collected from the monitor wells and SV-4 were analyzed for TPH-G by Method 8015M and BTEX and selected gasoline oxygenates/additives by EPA Method 8260B by • Excelchem Laboratories, Inc of Roseville, California (Excelchem) The selected oxygenates/additives Included methyl tert butyl ether (MTBE), ethanol (EtOH), tertiary-butanol (TBA), di-isopropyl ether (DIPE), ethyl-tert butyl ether (ETBE), tert-amyl methyl ether (TAME), 1,2-dichloroethane (1,2-DCA), and 1,2-dlbromoethane (EDB) Full gasoline oxygenate analyses for groundwater samples collected at the site was reinitiated in the January 2003 monitoring event in response to verbal requests from Jeff Wong of the SJCEHD In the February 4, 2003 letter, Mr Wong formally requested the continuation of the full gasoline oxygenate analyses for the site Mr Wong also requested that detection limits for MTBE and TBA be minimally set at or below the current MCLS for those chemicals (13 and 12 µg/L, respectively) These detection limits may not be possible to achieve in samples with high concentrations of other target analytes because the laboratory must dilute the samples to handle the higher concentration compounds without damaging the instrumentation However, at significant additional effort and expense, the laboratory was able to achieve the lower required detection limits for MTBE and TBA by reanalyzing the samples For the reanalysis, the laboratory ran selective mass spectrometry scans for the two compounds This technique ignores the other compound chromatogram peaks by isolating only the time window that the two compounds elute in Because of the time it takes to analyze and reanalyze the samples, the reanalysis had to be conducted on a rush basis to meet the sample holding times, further Increasing the cost of the work The current groundwater sample analytical results presented in 'I able 3, on the following page, are generally consistent with the historical results (Attachment C) although the limited amount of full gasoline oxygenate analyses (two recent monitoring events) makes historical comparison difficult Benzene and MTBE isoconcentration contour maps are included as Figure 4 and Figure 5,respectively, in AttaL,hrnent A The MTBE concentration detected In the groundwater sample collected from MW-3 is . slightly higher than detected in January 2003 (Figure 6, Attachment A) Laboratory certificates of analyses and chain of custody record are included in Attachment E S 4M il� CONDOR