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IT <br /> McDowell &Davis Towing <br /> Quarterly Groundwater Sampling Report August 2002 <br /> Page: 2 <br /> Groundwater Elevations 08-05-02 <br /> Well lCollar Eleva-ti-77 DTW GW Elevation <br /> MW-1 118.14 63.37 54.77 <br /> MW-2 118.79 63.96 54.83 <br /> MW-3 118.39 63.55 54.84 <br /> Groundwater flow was to the northeast (north 42 east) with a very shallow gradient <br /> (0.017 ft/ft). The potentiometric surface and groundwater flow direction are shown on <br /> Figure 2 Site Map / Groundwater Flow. Detectable concentrations of toluene (0.6 ug/1) <br /> and xylenes (1.1 ug/1), below water quality goals, were present in well MW2 located <br /> adjacent to the former underground storage tanks and fuel dispensers. Detectable <br /> concentrations of xylenes (1.2 ug/1), below water quality goals, were present in well <br /> MW3 <br /> MTBE was reported at a concentration of 2.0 ug/1 in well MW3. No other contaminants <br /> were reported for any of the monitoring wells. <br /> The dissolved oxygen concentrations show a very slight variation (6.1 to 6.5) a slight <br /> decrease compared to past monitoring events which indicates continued biologic activity <br /> in the area of the soil contamination. The slight variations in the dissolved oxygen <br /> concentrations suggest that that the release has not caused a significant groundwater <br /> impact. <br /> Laboratory Groundwater Sample Results (08-05-2002) <br /> Sample LD. Gasoline Benzene Toluene E-Benzene Xylenes Oxygenates Oz <br /> MW-1 <0.05 <0.3 <0.3 <0.3 <0.6 ND 6.1 <br /> MW-2 <0.05 <0.3 0.3 1 <0.3 10.9 ND 6.5 <br /> MW-3 <0.05 <0.3 <0.3 1 <0.3 1.2 2.0 MTBE 6.2 <br /> ND=Non Detect NA=Nat Analyzed <br /> Mg/L for gasoline gg/L for BTEX,MTBE,and 8260 Oxygenated Compounds <br /> Volatile aromatic hydrocarbons were detected in very low concentrations, below water <br /> quality goals, in monitoring wells MW-2 and MW3 in the August 2002 monitoring event. <br /> Previous monitoring events have detected gasoline and gasoline constituents at <br /> concentrations that exceeded established water quality goals. Gasoline and gasoline <br /> constituents have been detected in soil samples collected at depths of 15 and 25 feet in the <br /> vicinity of the former dispenser island. Scheduled quarterly groundwater monitoring will <br /> continue. <br /> A study consisting of a receptor / well survey, contaminant mass calculation, and <br /> evaluation of active remediation was submitted in May 2002. The study identified <br /> possible indoor air exposures to benzene vapors sourced from the shallow soil <br /> contamination that may exceed established standards. The San Joaquin County <br />