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Canepa's Car Wash 6230 Pacific Avenue Stockton,CA Second Quarter Groundwater Monitoring Report,April 2005 Page 4 of 10 LABORATORY ANALYTICAL RESULTS Groundwater samples collected from the monitoring wells and SV-4 were analyzed for total petroleum hydrocarbons quantified as gasoline (TPH-G) by EPA Method 8015M and benzene, toluene, ethyl benzene, and total xylenes (BTEX) and selected gasoline oxygenates/additives by EPA Method 8260B by Excelchem Environmental Labs of Eureka, California (Excelchem) The selected oxygenates/additives included 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-dibromoethane (EDB) The water samples collected from MW-1, the treatment system influent, and treatment system sampling points were analyzed for BTEX and selected gasoline oxygenates/additives by EPA Method 8260B by Argon Laboratories of Ceres, California (Argon) The selected oxygenates/additives included MTBE, TBA, DIPE, ETBE, and TAME The current groundwater sample analytical results (Table 3, on the next page) are generally consistent with the historic results with the exceptions of MW-1 and MW-11 because they are currently used as pumping wells for the treatment system (Table A, Attachment C) BTEX and MTBE concentrations in MW-1 I were relatively high during the January 2005 event, but have returned to historic levels BTEX and MTBE concentrations in MW-1 were relatively high during the January 2005 event, if compared to data collected before use as an extraction well, and have remained high None of the contaminants of concern were detected at or above the laboratory reported detection limits in monitoring wells MW-4, MW-9, and MW-12D The laboratory analytical results of the sample collected from MW-3 indicate that the MTBE concentration increased relative to the January 2005 sample (Figure 6, Attachment A) Contaminant concentrations in the sample collected from MW-1 decreased relative to the January 2005 monitoring event but remain, generally, close to the highest concentrations since June 1995 This increase is anticipated as the groundwater extraction draws the center of the contaminant plume toward it Benzene and MTBE iso-concentration contour maps are included as Figures 4 and 5, respectively, Attachment A Laboratory certificates of analyses and chain of custody records are included in Attachment F �y ��i CONDOR