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. April 15, 1993 Working To Restore Nature <br /> ARCO Facility No 6020, Manteca, California <br /> laboratory detection limits to 3 73 ppm Benzene concentrations ranged from below <br /> laboratory detection limits to 0 06 TPHg and benzene were not detected in soil sample <br /> collected from the stockpiled soil The analytical results of soil samples collected from the <br /> soil borings are summarized in Table 2 <br /> Ground-Water Flow Direction and Gradient <br /> We evaluated the ground-water gradient and the direction of groundwater flow at the site <br /> Tom O Morrow Inc (licensed land surveyors) of West Sacramento, California, surveyed the <br /> monitoring wells to provide the elevation of each wellhead relative to mean sea level Data <br /> were combined with the measured depths to ground water to calculate the elevation of the <br /> ground-water surface in each well These data were used to construct the Potentiometric <br /> Map presented on Plate 4 The evaluated groundwater flow direction on December 16, <br /> 1992, was toward the northwest with a hydraulic gradient of 0 014 This flow direction and <br /> gradient may be subject to seasonal fluctuations The ground-water elevations relative to <br /> mean sea level are shown in Table 4 <br /> Free-Phase and..Dissolved_Hydrocarbons in Ground Water <br /> Results of subjective analyses indicated monitoring wells MW-1 through MW-4 did not <br /> contain free product Laboratory analyses indicated dissolved gasoline and BTEX <br /> compounds were not detected in ground-water samples collected from monitoring wells <br /> MW-1 through MW-4 Nitrates were detected at concentrations of 1,200, 1,100, and 5,100 <br /> parts per billion in monitoring wells MW-1, MW-3, and MW-4, respectively The analytical <br /> results are summarized in Table 3 <br />. 30055-5 <br /> 8 <br />