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,t Canepa s Car Wash 6230 Pacific Avenue,Stockton,CA Fourth Quarter Groundwater Monitoring Report,October 2004 Page 3 of 6 . GROUNDWATER ELEVATIONS AND GRADIENT Groundwater elevation contours estimated for the shallow monitoring wells (MW-2,MW-4, MW-5, MW- 6, MW-7, MW-9, and MW-10) on October 14, 2004 indicate that the groundwater gradient is to the northeast and is generally consistent with previously estimated groundwater gradients (Figure 2, attached) Monitoring wells MW-3 and MW-12D were not used in groundwater elevation contouring due to an anomalous groundwater level measurement from MW-3 and MW-12D's deep screen interval An estimated groundwater gradient of 0 0055 ft/ft towards the northeast was measured using water level data from monitoring wells MW-6 and MW-9 The average depth to groundwater measured to the shallow monitoring wells for this event increased (decrease in water table elevation) by approximately 1 47 feet since July 22, 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 monitoring wells MW-2 through MW-7 were below the water table, consistent with much of the monitoring history at the site Table 2 Groundwater Elevation Data (October 14, 2004) Well Casing Screen Well Collar Depth to Water Groundwater WELL Interval (feet-bgs) Elevationt (feet) (feet) Elevation (feet) MW-1 50-70 1548 NM - MW-2 50-70 1529 4049 -2520 MW-3 50-70 15 53 4049 -2496 MW-4 50-70 15 83 41 72 -25 89 . MW-5 50-70 1471 4087 -26 16 MW-6 45-65 1489 3976 -2487 MW-7 45-65 15 80 4086 -2506 MW-9 25-45 1484 4097 -26 13 MW-10 25-45 1472 39 85 -25 13 MW-11 25-45 15 12 NM - MW-12D 100-110 1499 40 19 -2520 ' Well Collar Elevations are measured from a mark on the top of the well casing and are referenced to NGS benchmark HS0391 using NAVD 88 datum bgs=below ground surface NM=not measured 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/addittves by EPA Method 8260B by Excelchem Environmental Labs of Roseville, California (Excelchem) The selected oxygenates/additives included MTBE, ethanol (EtOH), tertiary-butanol (TBA), di-isopropyl ether (DIPS), 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 (Table 3 on the following page) are generally consistent with the historic results (Table A, Attachment C) 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 Monitoring well MW-12D has generally shown a decrease in contaminant concentrations each quarter since monitoring of the deep aquifer began to October of 2001 �� CONDOR