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Second Quarter,2002 Quarterly Groundwater Monitoring Report Canepa's Car Wash,Pacific Avenue,Stockton,CA Page 2 FIELD OBSERVATIONS On April 10 and 11, 2002, Condor representatives made field observations at the 12 site monitor wells (MW-1 through MW-11 and MW-12d). Field observations included water level measurement (Table 1, j below), appearance of samples (color, clarity, and presence of petroleum product sheen or phase in samples), and collection of water quality field parameters(Attachment D). GROUNDWATER ELEVATIONS AND GRADIENT The locations and top of casing elevations of the monitor wells were surveyed on November 26, 2001. The well locations are referenced to the NAD 83 datum and the well elevations are referenced to the NAVD 88 vertical datum from NGS benchmark.IS 1384. Groundwater elevation contours for the shallow monitor wells are shown on Figure 2, attached. The groundwater gradient is approximately 0.004 ft/ft to the cast-northcast as measured between monitor wells MW-6 and MW-3. A hydrograph of historic groundwater elevations is attached as Figure 3. Table 1 Groundwater Elevation Data (April 1.0,2002) Wel]Casing Well Collar Depth to Groundwater Screen WELL Elevation Water Elevation Interval (feet) (feet) (feet) (feet-bgs) MW1 50-70 15.48 33.11 -17.63 MW2 50-70 15.29 32.81 -17.52 vIW3 50-70 15.53 33.49 -17.96 1N4W4 50-70 15.83 33.67 -17.84 MW5 50-70 14.71 32.66 -17.95 13W6 45-65 14.89 32.18 -17.29 1SVV7 45-65 15.80 33.25 -17.45 vlw8 45-65 15.31 33.17 -17.86 MW9 25-45 14.84 32.84 -18.00 MW10 25-45 14.72 32.09 -17.37 14IW11 25-45 15.12 32.56 -17.44 MW12d 100-110 14.99 32.61 -17.62 LABORATORY ANALYTICAL RESULTS The groundwater samples collected from the monitor wells were analyzed for BTEX, TPH-G, and MTBE by Excelchem Laboratories, Inc. of Roseville, California. The current analytical results included in Table 2, on the following page, are generally consistent with the historical results (Attachment C) although gasoline constituent concentrations in the sample from MW-1 were significantly reduced. The MTBE concentration detected in the groundwater sample from monitor well MW-2 was higher than any historical MTBE detection at that well but is an estimated value only,due to coelution of peaks and retention time variations. Benzene and MTBE iso-concentration contour maps are included as Figure 4 and Figure 5, respectively, in Attachment A. The groundwater sample analytical results from wells MW 11 and MW-12d continue to indicate a trend of lower contaminant concentrations since the initial sampling event on October 25, 2001. The laboratory analytical results indicate a trend of increasing - • MTBE concentration at well MW-3 (Figure 6, Attachment A). Laboratory certificates of analysis and chain of custody record are included in Attachment E. +A `a CONDOR