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December 16 1992 AZffMfflqK <br /> , <br /> Unocal Service Station No 6981, Stockton, California Working To Restore Nature <br /> i <br /> decrease of approximately 4 5 feet The hydrocarbons are probably bound in <br /> the soil above the current groundwater resulting in lower dissolved <br /> concentrations in ground-water <br /> 1 o A vapor-extraction test performed at the site indicated that a radius of <br /> influence of 50 feet could be obtained using a flowrate of 80 cubic <br /> feet/minute The present location of the vapor-extraction wells appears to be <br /> sufficient utilizing a radius of 50 feet to successfully remediate the <br /> hydrocarbon containing soil However, additional shallow vapor-extraction <br /> wells may be required to address shallow soil near the dispenser islands <br /> o Based on the information to date, RESNA recommends the installation of <br /> additional vapor-extraction wells and a vapor-extraction system and continuing <br /> to perform quarterly ground-water monitoring at the site The remediation <br /> r of this soil should sufficiently reduce the source of hydrocarbons to the ground <br /> water RESNA recommends that the active remediation of ground water by <br /> extraction and treatment be deferred until the source of the plume, the <br /> overlying hydrocarbon containing soil, is sufficiently remediated and is no <br /> longer a source of hydrocarbons to the ground water <br /> r <br /> LIMITATIONS <br /> r This report was prepared in accordance with generally accepted standards of environmental <br /> geological practice in California at the time this investigation was performed This <br /> investigation was conducted solely for the purpose of evaluating environmental conditions <br /> r of the soil and ground water with respect to hydrocarbon product, and selected chemicals <br /> on the site No soil engineering or geotechnical references are implied or should be <br /> inferred Evaluation of the geologic conditions at the site for the purpose of this <br /> investigation is made from a limited number of observation points Subsurface conditions <br /> may vary away from the data points available Additional work, including further subsurface <br /> investigation, can reduce the inherent uncertainties associated with this type of investigation <br /> r <br /> 33032-10 18 <br /> r <br />