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n <br /> Groundwater Extraction and Treatment System Evaluation June 5, 1993 <br /> Sebastian Vineyards/Woodbridge Cellars CEECON <br /> conducted by McLaren between May and June 1989 to evaluate the lateral and vertical <br /> extents of gasoline hydrocarbons in the soil and groundwater beneath the subject site. This <br /> investigation consisted of drilling fifteen soil borings, ten of which were completed as <br /> groundwater monitoring wells. Results of the initial subsurface environmental investigation <br /> indicated soils in the immediate vicinity of the former tank and groundwater beneath the <br /> site were impacted by gasoline hydrocarbons. McLaren concluded that remediation of the <br /> soil and groundwater was necessary. <br /> Re "onal and Local Geology and H droBology <br /> The site lies in the median portion of the Central Valley of California. The Central Valley <br /> is a broad geosynclinal trough that is filled with Quaternary- to Tertiary-age sedimentary <br /> deposits. The upper portion of sediments within the Central Valley consists mainly of <br /> unconsolidated Pleistocene- to Recent-age alluvial fan and lacustrine deposits up to <br /> approximately 10,000 feet in thickness. The subject site is underlain with a sequence of silts <br /> and sands with varying amounts of clays (Waterwork, November 10, 1990). Soils <br /> encountered from ground surface to approximately 17 feet below ground surface (bgs) are <br /> silty to sandy clays with low porosity. Soils encountered from 17 feet to approximately 34 <br /> feet bgs are silty to clean sands with moderate porosity. The geologic setting at the subject <br /> site is depictive of a flood plain environment, with a series of low energy channel and levee <br /> deposits. Groundwater is at approximately 18 feet bgs in the silty to clean sand unit <br /> encountered at approximately 17 feet bgs to approximately 34 feet bgs. The shallow <br /> groundwater beneath the site flows through low to moderately permeable silty sands to the <br /> southeast with a hydraulic gradient of approximately 0.005 foot per feet (ft/ft). <br /> GROUNDWATER TREATMENT SYSTEM <br /> The trailer-mounted groundwater treatment system, including water filters, an aeration <br /> system, a water hardness chemical injector, and activated carbon polishing, was installed by <br /> CEECON on September 21, 1992, and is currently operating at the site. Instrumentation <br /> and controls on this system include water level indicators, transfer pumps, flow indicator, <br /> 2 <br />