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Third Quarter(2003 Annual Event)Groundwater Monitoring Report Canepa s Car Wash,Pacific Avenue,Stockton,CA Page 3 GROUNDWATER ELEVATIONS AND GRADIENT Groundwater elevation contours estimated for the shallow monitor wells (MW-1 through MW-7 and MW-9 through MW-11) on July 25, 2003, Indicate that the groundwater gradient is to the east 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 0036 ft/ft towards the northeast was measured using water level data from monitor wells MW-9 and MW-10 The average depth to groundwater measured in the 11 monitor wells at the site increased by approximately 1 10 feet since April 17, 2003 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 25, 2003) Well Casing Well Collar Depth to Groundwater WELL Screen Elevation Water Elevation Interval feet-b s (feet) (feet) (feet) MW-1 50-70 1548 3678 -21 30 MW-2 50-70 1529 3646 -21 17 MW-3 50-70 1553 37 19 -21 66 MW-4 50-70 15 83 3730 -21 47 MW-5 5070 1471 3633 -21 62 MW-6 45-65 1489 3575 -2086 MW-7 45-65 1580 3690 -21 10 MW-9 2545 1484 3650 -21 66 MW-10 25-45 1472 3557 -2095 MW-11 25-45 1512 3614 -2102 MW-12D 100-1 l0 14 99 3639 21 40 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 Laboratories, Inc of Roseville, California (Excelchem) The selected oxygenates/additives included methyl tert butyl ether (MTBE), ethanol, tertiary-butanol (TBA), di-isopropyl ether (DIPE), ethyl-tent 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 presented in Table 3, on the following page, are generally consistent with the historical results (Attachment C) although the limited amount of full gasoline oxygenate analyses (three recent monitoring events) makes historical comparison difficult For the first time in the monitoring history of deep monitor well MW-12D, none of the contaminants of concern were detected at or above the laboratory reported detection limits TBA and TAME were detected in the sample collected from MW-3 for the first time (1 10 and 1 3 tig/L, respectively) The concentration of MTBE detected in the groundwater sample collected from MW-3 is consistent with an increasing trend for that contaminant in that well (Figure 6, Attachment A) Benzene and MTBE iso-concentration contour • maps are included as Figures 4 and 5, respectively, in Attachment A Laboratory certificates of analyses and chain of custody record are included in Attachment E �'� CONDOR