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Canepa's Car Wash 6230 Pacific Avenue,Stockton,CA Second Quarter Groundwater Monitoring Report,May 2004 Page 3 of 5 . GROUNDWATER ELEVATIONS AND GRADIENT Groundwater elevation contours estimated for the shallow monitor wells (MW-1, MW-3, MW-4, MW-5, MW-6, MW-7, MW-9, MW-10, and MW-11) on May 7, 2004 indicate that the groundwater gradient is to the northeast and is generally consistent with previously estimated groundwater gradients (Figure 2, attached). Monitor well MW-12D was not used in groundwater elevation contouring due to the well's deep screen interval. An estimated groundwater gradient of 0.0045 ft/ft towards the northeast was measured using water level data from monitor wells MW-6 and MW-5. The average depth to groundwater measured in the shallow monitor wells for this event decreased (increase in water table elevation) by approximately 0.28 feet since January 30, 2004. A hydrograph of historic groundwater elevations is attached as Figure 3. 1t should be noted that the top of the well screens for shallow monitor wells MW-1 through MW-7 were below the water table, consistent with much of the monitoring history at the site. Table 2 Groundwater Elevation Data (May 7, 2004) Well Casing Well Collar Depth to Groundwater Screen WELL Elevation Water .Elevation Interval feet-b s (feet) (feet) (feet) MW-1 50-70 15.48 37.72 -22.24 MW-2 50-70 15.29 37.32 -22.03 MW-3 50-70 15.53 38.20 -22.67 MW4 50-70 15.83 38.46 -22.63 MW-5 50-70 14.71 37.54 -22.83 MW-6 45-65 14.89 36.66 -21.77 MW-7 45-65 15.80 37.69 -21.89 MW-9 25-45 14.84 37.66 -22.82 MW-10 25-45 14.72 36.72 -22.00 MW-11 25-45 15.12 37.07 -21.95 MW-12D 100-110 14.99 37.03 -22.04 LABORATORY ANALYTICAL RESULTS The groundwater samples collected from the monitor wells and SV-4 were analyzed for TPH-G by 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 Roseville, California (Excelchem). The selected oxygenates/additives included methyl tert-butyl ether (MTBE), ethanol, tertiary-butanol (TBA), di-isopropyl ether (D1PE), ethyl tert-butyl ether (ETBE), ter -amyl methyl ether (TAME), 1,2-dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB). The current groundwater sample analytical results (see Table 3) are generally consistent with the historical results (Table A, Attachment Q. None of the contaminants of concern were detected at or above the laboratory reported detection limits in monitor wells MW-9 and MW-12D. Monitor well MW- 12D has generally shown a decrease in contaminant concentrations each quarter since monitoring of the deep aquifer began in October of 2001. Contaminant concentrations in the sample collected from MW-3 are reduced relative to recent monitoring events. The concentration of MTBE detected in the groundwater sample collected from monitor well �1� CONDOR