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=EsMw <br /> Working To Restore Nature <br /> April 15, 1993 <br /> ARCO Facility No 6020, Manteca, California <br /> hydrocarbons were present in the soil (Applied Geosystems, October 3 1990) Approximate <br /> locations of soil borings are presented on Plate 2 <br /> This investigation was preliminary, and was not in response to a known or suspected release <br /> Results of laboratory analyses indicated that relatively low levels of gasoline hydrocarbons <br /> were detected in samples collected from borings B-3 through B-6 (Table 2) Total <br /> petroleum hydrocarbons as gasoline and benzene concentrations ranged from below <br /> laboratory detection limits to 3 7 parts per million and below laboratory detection limits to <br /> 0 06 parts per million, respectively <br /> REGIONAL GEOLOGY AND HYDROGEOLOGY <br /> The site area is underlain by alluvial fan deposits of the Great Valley that are of Recent <br /> age These sediments consist of unconsolidated clay, silt, and sand (Rogers, 1966) The <br /> topographic surface is nearly flat with a slight westward slope Based on regional maps <br /> prepared from 1988 ground-water data by San Joaquin County Flood Control and Water <br /> Conservation District, ground water near the site is approximately 25 below grade and the <br /> regional direction of flow is to the southwest Local ground-water at the time of drilling was <br /> encountered between 21 and 24 feet below grade <br /> The site is in the Eastern San Joaquin County Ground-Water Basin (California Department <br /> of Water Resources, 1980) The ground-water basin has been developed for intensive <br /> irrigation, domestic, industrial, municipal, and stock use <br />. 3MS-5 <br /> 3 <br />