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QUARTERLY MONITORING REPORT AUGUST 1996 CANEPA S CAR WASH 6230 Pacific Avenue Stockton CA September 11 1996 4 3 Groundwater Gradient iOn August 1, 1996, the depth to groundwater was measured in each monitor well prior to the collection of groundwater samples The average depth to groundwater was approximately 44 feet ' below the ground surface (bgs) at the site Because monitor wells MW-1, MW-2, MW-3, MW-4, and MW-5 are screened from approximately 50 to 70 feet bgs and monitor wells MW-6, MW-7, and MW- 8 are screened from approximately 45 to 65 feet bgs, the water level in all of the wells was above the top of the well screens The groundwater elevation ranged from 3144 to 30 37 feet below sea level (bmsl) See Table 2, below for groundwater elevation data Groundwater elevation contours are shown in Figure 3, Appendix A A hydrograph of groundwater elevations is Included as Figure 4, Appendix A The accompanying Hydrograph Table Includes historical groundwater elevation data r TABLE 2 Groundwater Elevation Data (August 1, 1996) MW-1 through MW-8 -T ' Well Well Collar Eievahon Depth to Groundwater Elevation Number (feet) Water(feet) (feet) NM-I 1345 43 82 -1037 MW-2 13.27 4369 -3042 NM-3 13 50 44 25 -3075 NM-4 13 82 4432 -30 50 6113-5 1269 41 34 -3065 AIA 6 1162 4106 -3144 11!11-7 13 18 44 15 -1097 nn1-g 1126 44 11 30 8a r5.0 DISCUSSION OF RESULTS ' The results of the laboratory analyses Indicate that TPH-G, BTEX, and MTBE were detected in groundwater samples collected during the sampling event Benzene concentrations detected in MW- 1, MW-2, MW-6, and SV-7 exceed the maximum contaminant level (MCL) for benzene (1 0 ug/L) in ' drinking water (California Code of Regulations, Title 22, Drinking Water Regulatory Criteria) No MCL has yet been established for MTBE The California Department of Health Services has set an action level of 35 gg/L for MTBE in drinking water, however MTBE concentrations detected in MW-1 and SV-7 exceed that level The TPH-G and BTEX analytical results for the August 1996, sampling are generally consistent with historical analytical results However, TPH-G and BTEX concentrations are generally Page -4- ' t, N L W— CONDOR