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August 18, 1993 WA <br /> Unocal Service Station No 6981, Stockton, CaliforniaWorking To Restore NA ure <br /> 1n August 1992 and are used to delineate hydrocarbons in groundwater (RESNA, December <br /> 16, 1992) <br /> In March 1992, a vapor-extraction test was performed at the site Results of this test <br /> indicated that using a wellhead flowrate of 80 cubic feet per minute, an effective radius of <br /> influence of approximately 50 feet would be achieved per well (RESNA, June 29, 1992) <br /> In August 1992, a groundwater pumping test was performed onsite (RESNA, May 4, 1993) <br /> This test was performed to evaluate hydrologic and well conditions and provide baseline <br /> information for the possible design and operation of a groundwater remedial system Pump <br /> test data indicated that the aquifer beneath the site is heterogeneous, anisotropic, and <br /> unconfined with a transmisslvity of 0 4 to 0 8 foot per minute and a specific yield of 5 to 10 <br /> percent Using a pumping rate of 3.5 gallons per minute, a radius of capture of 18 feet was <br /> observed <br /> REGIONAL GEOLOGY AND HYDROLOGY <br /> Unocal Service Station No 6981 is in the Central Valley geomorphic province of California, <br /> which is a northwestward-trending, asymmetric structural trough that has been filled with <br /> 6 to 10 miles of sediment ranging in age from Jurassic to Holocene (Page, 1986) The <br /> topographic surface is nearly flat with a slight westward slope Based on an extrapolation <br /> of a geological map prepared by Marchand and Atwater (1979), sediments beneath the site <br /> consist of Quaternary alluvial deposits of the Modesto Formation, which were deposited by <br /> the Mokelumne River The nearest surface stream is the Calaveras River which trends east <br /> and west approximately 1,800 feet southeast of the site <br /> 38032-14W 4 <br />