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Canepa s Car Wash tr� 6230 Pacific Avenue,Stockton,CA Third Quarter Groundwater Monitoring Report,July 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, MW-10, and MW-11) on July 22, 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 0047 ft/ft towards the northeast was measured using water level data from monitor wells MW-6 and MW-9 The average depth to groundwater measured in the shallow monitor wells for this event increased (decrease in water table elevation) by approximately 1 64 feet since May 7, 2004 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 (July 22, 2004) Well Casing Well Collar Depth to Groundwater WELL Screen Elevation Water Elevation Interval (feet) (feet) (feet) feet-b s MW-1 50-70 1548 3944 -23 96 MW-2 50-70 15 29 3900 -2371 MW-3 50-70 15 53 3991 -2438 MW-4 50-70 15 83 4010 -2427 . MW-5 50-70 1471 3922 -2451 MW-6 45-65 1489 3829 -23 39 MW-7 45-65 1580 3937 -2357 MW-9 25-45 1484 3932 -2448 MW-10 2545 1472 3826 -2354 MW-11 25-45 1512 3868 -2356 MW-12D 100-110 1499 3892 -23 93 LABORATORY ANALYTICAL RESULTS The groundwater samples collected from the monitor wells and SV4 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), 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 (Table A, Attachment C) None of the contaminants of concern were detected at or above the laboratory reported detection limits in monitor wells MW-4, MW-6, MW-7, MW-9, MW-10 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 • s �J CONDOR