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Canepa's Car Wash 6230 Pacific Avenue,Stockton,CA First Quarter Groundwater Monitoring Report,January 2004 Page 3 of 6 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, and MW-10) on January 30, 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 .0061 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 six of the sites ten shallow monitor wells for this event decreased by approximately 0.55 feet since November 9, 2003. Monitor wells MW-2, MW-5, MW-10, and MW-1 I were not used in calculation of the average because data obtained during the November 2003 monitoring event from monitor wells MW-2 and MW-11 is believed to be erroneous and monitor wells MW-5 and MW-10 had been paved over and were not relocated until after the November monitoring event. A hydrograph of historic groundwater elevations is attached as Figure 3. It 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 (January 30, 2004) Well Casing Well Collar Depth to Groundwater Screen WELL Elevation Water Elevation Interval (feet) (feet) (feet) feet-b s MW-1 50-70 15.48 37.94 -22.46 0 MW-2 50-70 15.29 37.43 -22.14 MW-3 50-70 15.53 38.51 -22.98 MW-4 50-70 15.83 38.89 -23.06 MW-5 50-70 14.71 38.07 -23.36 MW-6 45-65 14.89 36.80 -21.91 MW-7 45-65 15.80 37.77 -21.97 MW-9 25-45 14.84 38.11 -23.27 MW-10 2545 14.72 37.05 -22.33 MW-11 25-45 15.12 37.20 -22.08 Mw-12D 100-110 14.99 37.06 -22.07 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 Environmental Labs of Roseville, California (Excelchem). The selected oxygenates/additives included methyl tert butyl ether (MTBE), ethanol, 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 current groundwater sample analytical results (see Table 3) are generally consistent with the historical results (Attachment C) although the limited number of full gasoline oxygenate/additives analyses (five recent monitoring events) makes historical comparison difficult. None of the contaminants of concern were detected at or above the laboratory reported detection limits in monitor well MW-9. The �� CONDOR