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S wwww'� <br /> '-6m-, <br /> v,c'c. €y �� i. 'moi:. � •_' 9i Y� _ '-sal,:.i..'f1iH.Ya' ..+e3 iFa++M_'�5�: <br /> GASCO Gasoline Station February 8, 1991 <br /> Project No. 3-30054-31 Page 1 <br /> •a WORK PLAN FOR A <br /> SUPPLEMENTAL SOIL AND GROUNDWATER <br /> INVESTIGATION <br /> AT <br /> GASCO GASOLINE STATION <br /> 749 EAST CHARTER WAY <br /> STOCKTON, CALIFORNIA <br /> At the request of Darpetrol, Inc., ExceItech, Inc., has prepared this work plan for a <br /> 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, and super unleaded gasoline. The 1ccations 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 /> (CGG). <br /> In November 1989, four underground fuel storage tanks, located in 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 /> from 1.5 to 3.500 parts per million (ppm). The excavation was backfilled with the <br /> original soil plus soil from the excavation for new tanks. <br /> In December 1989, an electromagnetic induction survey was conducted at the site as a <br /> preliminary plume investigation technique and to aid in thu 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, CGG installed three groundwater monitoring wells on the site at the <br /> -- locations shown on Figure 2. They were designated BM-1, BM-2, and BM-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 230,000 ppb at BM-1. Benzene ranged from 92 ppm at BM-3 to <br /> 26,000 ppb at BM-1. <br /> f ; <br /> r� <br /> k _ <br /> 't-s <br />