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McDowell&Davis Towing Quarterly Groundwater Sampling Report December 2003 Page: 2 approximately 0.25 feet from the August 4, 2003 monitoring event. A groundwater hydrograph is presented in Figure 4. Groundwater Elevations 12 - 08 - 03 Well Collar Elevation DTW GW Elevation MW-1 118.14 64.71 53.43 MW-2 118.79 65.32 53.47 MW-3 118.39 64.97 53.42 Groundwater flow was to the west (south 82 west) with a very shallow gradient (0.0012 ft/ft). The potentiometric surface and groundwater flow direction are shown on Figure 2 Site Map / Groundwater Flow. Gasoline range petroleum hydrocarbons, aromatic compounds, and MTBE were not detected in any of the monitoring wells. The dissolved oxygen concentrations ranged from 9.1 to 11 mg/l indicting a decrease in biologic activity possibly related to the biologic reduction of the residual groundwater contamination. The minor drop in oxygen concentrations is consistent with the detection of trace contaminant concentrations in well MW3. Laboraton Groundwater Sample Results 12-8-03 Sample I.D. Gasoline Benzene Toluene E-Benzene Xylenes Oxygenates Oz MW-1 <0.05 <03 <0.3 <0.3 <0.6 ND 11 MW-2 <0.05 <0.3 <0.3 1 <0.3 <0.6 ND 11 MW-3 0.05 0.3 10.8 0.3 1.3 1 ND 1 9.1 ND—Non Detect NA=Not Analyzed Mg/L for gasoline gg/L for BTEX,MTBE,and 8260 Oxygenated Compounds Volatile aromatic hydrocarbons and petroleum hydrocarbons were not detected in any of the monitoring wells in the August 4, 2003 monitoring event. Previous monitoring events detected gasoline and gasoline constituents at concentrations that exceeded established water quality goals. Gasoline and gasoline constituents have been detected in soil samples collected at depths of 15 and 25 feet in the vicinity of the former dispenser island. An additional exploratory boring was constructed on August 6, 2003 to further define the mass of impacted soil and recalibrate the fate and transport modeling and risk assessment for the site. A report of the investigation including a revised evaluation of the risk posed by vapor transport of the benzene contamination in the soil shallow soils has been submitted to San Joaquin County Environmental Health Department. Scheduled quarterly groundwater monitoring will continue as directed by the Department.