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June 26, 1992 <br /> iARCO Service Station No. 549, Stockton, California <br /> 6.0 ppm, total nickel at concentrations of 46.3 ppm and 41.5 ppm, and total zinc at <br /> concentrations of 61.9 and 63.8 ppm. TOG concentrations were detected at 74 ppm and 140 <br /> ppm in samples from boring B-12. <br /> The composite soil sample collected from the stockpiled soil contained TPHg at a <br /> concentration of 44 ppm. Benzene and toluene were reported to be below laboratory <br /> detection limits, and ethylbenzene and total xylene isomer concentrations were reported at <br /> 0.047 and 0.28 ppm, respectively. The analytical results of soil samples collected from the <br /> soil borings and the stockpiled soil are summarized in Table 3. Appendix B contains the <br /> laboratory reports and Chain of Custody Records. <br /> Ground-Water Flow Direction and Gradient <br />� . We evaluated the ground-water gradient and the direction of ground-water flow at the site. <br /> Tom O. Morrow, Inc. (licensed land surveyors) of West Sacramento, California, surveyed <br /> the monitoring wells to provide the elevation of each wellhead relative to mean sea level. <br />. Data were combined with the measured depths to ground water to calculate the elevation <br /> of the groundwater surface in each well. These data were used to construct the <br /> Potentiometric Map presented on Plate 28. <br /> Based on the <br /> potentio metric data, the ground-water flow direction on October 30, 1991, was _s <br /> �__.T — _.._ . . - - <br /> Llightly south of east with a hydraulic gradien -f 0_.0Q.J The flow direction and gradient <br /> may be subject to seasonal fluctuations. <br /> 3000a 9 <br />