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r r Canepa's Car Wash 6230 Pacific Avenue, Stockton, California April 28, 1994 Phase II Site Characterization Page: 6 ' 5.0 Groundwater Conditions ' The water table was approximately 52 to 55 feet below ground level as the borings were being drilled Subsequent water sampling of all monitoring wells recorded water levels as shown in Table 1 &Appendix G rThe groundwater measurements from the initial sampling event of November 1, 1993 were used to construct the gradient as shown on Figure 11 The groundwater contours indicate a trough dipping due North and averaging 0 009 ft/ft The wells were measured again on December 7, 1993 and another gradient was calculated The gradient direction had moved 60 degrees to the east and had flattened to an average of 0 004 f1/ft During that 37 day period, water levels rose in all wells an average of 0 65' On December 29, 1993, additional water level measurements were taken while verifying the well collar elevation survey, and another gradient was calculated During the intervening period of 22 days, the gradient increased only 0 001 ft/ft to 0 005 ft/ft at N 70 E Again the water levels rose an average of 0 50' Laboratory analysis for the first round of wells show benzene, toluene, xylene and gasoline contamination m MW-1, 2, and 4 MW-3 only had a trace (0 18 mg/L) of gasoline contamination (Figure 10, Table 7,&Appendix E) After MW-5, 6, 7 8r 8 were installed, all wells were surveyed, measured and sampled Another gradient was calculated from the March 30, 1994 data The resulting map shows a mound in the water table that can only be caused by recharge (leakage) into the groundwater in the "ci sty of MW-1 & 2 (Figure 11) It would appear that the local gradient is to the east- nortbeast, because of the steep gradient on the west side of the mound and the flatter gradner is on the east side This correlates with data from the San Joaquin County Flood Control and Water Conservation District map showing Lines a Eaual Elevation Of Water In Wells. ring 1983. The sampling event of March 30, 1994, included the original monitoring wells MW-1, 2, 3 &4 and the additional "step-out" monitoring wells MW-5, 6, 7 & 8 That data constitutes the first quarterly groundwater sampling report and has been incorporated into the body of this report Wells MW-1, 2, 6, 7 & 8 have BTE&X and gasoline contamination Wells MW-3, 4 & 5 all tested ND(Table 7) F 0 Geology . This site, at 6230 Pacific Avenue, Stockton, California, is located in the northern end of California's San Joaquin Valley This area is monotonous geologically, representing primarily