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ADDITIONAL GROUND WATER MONrTORING WELL INSTALLATION AND <br /> UARTERLY GROUND WATER MONITORING REPORT FIRST QUARTER 1992 <br /> Eason Station RIS 7-3708 <br /> 2705 Country Club Boulevard <br /> Stockton, California <br /> Delta Project No 40-91-838 <br /> Page 8 <br /> 4.0 DISCUSSION <br /> Depth to ground water beneath the site ranged between 11.22 and 13 82 feet below the top of casings on <br /> ' March 18, 1992, indicating a ncrease in water elevations since December 1991 (Table 2) The direction <br /> of ground water flow is towards the northeast at an average gradient of 0 001 <br /> During the March 18, 1992, sampling event, petroleum hydrocarbons were not detected in the ground <br /> water sample collected from the new off-site monitoring well MW-4 or existing monitoring well MW-1 <br /> The ground water samples collected from existing on-site monitoring well MW-2 and newly Installed <br /> off-site monitoring wells MW-5 and MW-6, on March 18, 1992, reported 0 9 ppb, 0 6 ppb and 0 6 ppb <br /> benzene and below the laboratory detection limits for toluene, ethylbenzene, xylenes and TPH as gasoline_ <br /> ' The ground water sample collected from monitoring well MW-3 during the March 1992 sampling event <br /> was reported below the laboratory detection limit for xylenes, 79 ppb, 0 5 ppb and 0 7 ppb benzene, <br /> ethylbenzene and xylenes, respectively, and 170 ppb TPH as gasoline The Inferred distribution of <br /> dissolved benzene and TPH as gasoline in ground water beneath the site is illustrated in Figures 4 and 5 <br /> ' Ground water levels and round water quality will continue to be monitored on a quarterly basis The <br /> g 9 y <br /> ' next ground water sampling event is scheduled for June 1992 <br /> ' RPT 112 JDM <br />