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I. <br /> Quarterly Ground-Water Monitoring May 10, 1990 <br /> Beacon Station No. 502, Lodi, California AGS 86091-7 <br /> Fuel Tanks (LUFT) Method and for benzene, toluene, ethylbenzene, and total xylene <br /> isomers (BTEX) by Environmental Protection Agency Method 602. Copies of the <br /> laboratory analysis reports are attached. The results of these analyses and previous <br /> laboratory analyses are summarized in Table 1. <br /> The results of the laboratory analyses indicate that hydrocarbon constituents were not <br /> detected in the five ground-water samples. Hydrocarbon concentrations in the samples fron, <br /> the five monitoring wells have steadily decreased since the October 1986 monitoring event, <br /> >' as shown in Table I. The hydrocarbon concentrations from this monitoring event continue <br /> that downward trend. <br /> Applied GeoSystems evaluated the ground-water gradient across the site. The elevation of <br /> the top of the casing in each well was surveyed by Moldenhauer Engineering Company, a <br /> licensed land surveyor from Davis, California, on November 27, 1989. Elevations were <br /> measured in feet relative to mean sea level, using a local U.S. Geological Survey benchmark <br /> as a datum. The measurements of the depths to ground water were combined with the <br /> casing elevations to calculate the ground-water elevations. These data are summarized in <br /> Table 2 and were used to evaluate the ground-water gradient at the time of this quarterly <br /> monitoring event (Plate P-3). The average ground-water gradient assuming isotropic <br /> conditions was evaluated to be 0.010, with a flow direction towards the south-southeast; the <br /> magnitude .�f the gradient appears to vary across the site. The direction of the ground- <br /> water gradient is similar to that evaluated in previous sampling events. <br /> tip <br /> r 2 <br /> :w <br /> Aop/isd GsOsystsms <br />