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2905 West Benjamin Holt Drive, Stockton, California March 16, 1994 <br /> Chevron U.S.A. Products Company Page 2 <br /> y,r <br /> 2.0 BACKGROUND <br /> 2.1 Site Information <br /> The site is an active service station located on the southwest corner of West Benjamin Halt Drive <br /> intersection and Plymouth Road in Stockton, San Joaquin County, California. Currently the service <br /> station operates two pump islands supplied by four underground storage tanks (USTs) containing three <br /> grades of unleaded gasoline, a small convenience market and a car wash (Figure 2). The site is located <br /> approximately 0 to 5 feet above sea level and the site topography is flat. Local surface drainage is to <br /> the west and controlled by a number of sloughs, canals and ditches. The site is bordered to the east by <br /> Swenson Park Golf Course, to the west by Interstate 5, to the north by a residential development, and to <br /> the south by an ARCO service station with known soil and groundwater contamination. <br /> The Chevron service station was demolished in late 1988 to early 1989 and remodeled into the current <br /> configuration in 1991. In the former arrangement, one 6,000-gallon and two 10,000-gallon fiberglass <br /> USTs storing gasoline rested approximately 12 feet below ground surface in a UST pit located beneath <br /> the southwestern portion of the site (Figure 2). The former pump islands were located just west of the <br /> tank pit and aligned parallel to West Benjamin Holt Drive. A service station building and a 550-gallon <br /> fiberglass used-oil tank were located near the location of the present USTs (Figure 2). The three former <br /> gasoline USTs, the used-oil UST, service station building and associated piping were removed in 1989 <br /> during demolition. No holes were noticed in the tanks when removed (Blaine Tech Services, Inc., 1989). <br /> Initial soil assessment was started during tank removal as required by San Joaquin County Public Health <br /> Services (SJCPHS). Subsequent soil and groundwater assessment since 1989 has included new and <br /> former tank-pit soil sampling, product-line trench soil sampling, soil-vapor surveying, groundwater <br /> monitoring and vadose well installation, and quarterly groundwater monitoring and sampling in an <br /> attempt to define the limits of hydrocarbon-impacted material. Described below are the cumulative <br /> results of soil and groundwater assessment. <br /> 2.2 Results of Soil Assessment <br /> Assessment of soil at the site has proceeded in three phases: UST-pit and product-line soil sampling, a <br /> soil-vapor survey, and soil sampling of borings for groundwater monitoring well and vadose well <br /> installation. The results of petroleum hydrocarbon analyses of soil samples collected during each phase <br /> 5073PAR.RPT '��7n <br /> r GROUNDWATER <br /> �' TECHNOLOGY <br />