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E� <br /> -4 <br />,µms <br /> GASCO Gasoline Station February 8, 1991 <br /> Project No. 3-30054-31 Page 1 <br /> WORK PLAN FOR A <br /> SUPPLEMENTAL SOIL AND GROUNDWATER <br /> INVESTIGATION <br /> AT <br /> GASCO GASOLINE STATION <br /> 749 EAST CHARTER WAY <br /> :eTO KTON9 CALIFORNIA <br /> At the request of Darpetrol, Inc., Exceitech, Inc., has prepared this work plan for a <br /> ry supplemental soil and groundwater investigation at the subject site in the City of <br /> Stockton, San Joaquin County, California (Figure 1). <br /> BACKGROUND <br /> The station uses three underground fuel storage tanks and two pump islands, which <br /> store and dispense regular, unleaded, anti super unleaded gasoline, The locations of the <br /> tanks, pumps, and station building are shown in Figure 2. The following background <br /> narrative is from a site assessment report by California Geophysical Group, Inc. <br /> (COG). <br /> In November 1989, four underground fuel storage tanks, located it! the approximate <br /> southeastern corner of the site, were removed during site renovation. Two soil samples <br /> were collected from beneath each of the tanks. Laboratory results revealed that total <br /> petroleum hydrocarbons as gasoline (TPHG) were detected at concentrations ranging <br /> i. from 1.9 to 3,600 parts per million (ppm). The excavation was backfilled with the <br /> original soil plus soil from the excavation for new tanks. <br /> E • In December 1989, an electromagnetic induction survey was conducted at the site as a <br /> preliminary plume investigation technique and to aid in the placement of groundwater <br /> monitoring wells. An original work plan for site investigation was also completed and <br /> submitted to the San Joaquin Local Health Department. <br /> ' In January 1990, CCG installed three groundwater monitoring wells on the site at the <br /> y Iocations shown on Figure 2. They were designated RM-1, BM-2, and ISM-3. Soil <br /> samples Collected during the well installation were reported to contain petroleum <br /> hydrocarbons. TPHG concentrations were detected in soil samples from boring BM-1 <br /> and ranged from 28 to 6,100 ppm. Petroleum hydrocarbons were detected in <br /> groundwater samples from all three wells. TPHG ranged from 92 parts per billion <br /> (ppb) at BM-3 to 230,OOU ppb at BM-1. Benzene ranged from 92 ppm at Bill-3 to <br /> r 26,000 ppb at B M-1. <br /> Iu <br /> tS <br />