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May 4, 1993 ffAOMAA <br /> Unocal Station No 6981, Stockton, California Working To Restore Nature <br /> 5.3.2 Ground-Water Extraction and Treatment <br /> Based on data available at this time, it appears that the overlying soil contains residual <br /> hydrocarbons from approximately 15 feet below surface grade to approximately 55 feet <br /> Pump test data indicate that utilizing a pumping rate of 3 5 gallons per minute, the average <br /> calculated transmissivity, and the measured ground water gradient, a calculated radius of <br /> capture for the pumping test well is only 18 feet Due to this minimal capture radius for <br /> groundwater pumping and the current presence of a source of hydrocarbons in the overlying <br /> soil, the extraction and treatment of ground-water at this time may not be a cost affective <br /> approach and have a minimal affect on the presence of dissolved hydrocarbons in ground- <br /> water <br /> 6.0 RECOMMENDED REMEDIAL ACTION <br /> i � <br /> Based on the results presented in the Problem Assessment Report and our evaluation of site <br /> conditions and remedial alternatives, we recommend that active remediation of ground <br /> water by extraction and treatment be deferred until the source of the dissolved plume, the <br /> 1 overlying hydrocarbon containing soil, is sufficiently remediated to no longer be a source of <br /> hydrocarbons to the ground water To address the hydrocarbons in soil, we also recommend <br /> the installation of two additional shallow vapor-extraction wells Concurrently with soil <br /> remediation, quarterly ground-water monitoring should continue to monitor the possible <br /> migration of the dissolved plume and the effectiveness of the vapor-extraction remediation <br /> system <br /> 70 PERMITS <br /> Prior to installing the additional vapor-extraction wells, permits will be obtained from the <br /> San Joaquin County Department of Public Health Services In addition to the well permits, <br /> permits for the system will also be obtained The Authority to Construct and the Permit to <br /> Operate will be obtained Permits from the Building Department for the City of Stockton <br /> 38032-13 12 <br />