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i <br /> Section 2 <br /> Field Investigation and Methodologies <br /> The following subsurface investigation techniques were implemented: soil-gas survey, <br /> soil borings, subsurface soil sample collection and analysis, groundwater monitoring <br /> wells, and groundwater sample collection and analysis. The purpose of the activities is <br /> described below. <br /> Task Purpose _ <br /> Qualitatively delineate the shallow vertical and lateral extent of <br /> Soil-gas Survey contamination in the vicinity of the former gasoline tanks and <br /> f gasoline dispensing islands. <br /> Soil Borings Assess the potential vertical and horizontal extent of <br /> contamination from the former tank pit. <br /> Monitoring Wells Assess onsite extent of petroleum hydrocarbons in groundwater. <br /> This section describes the methods used to obtain the desired data. Observations and <br /> results are presented in Section 3. <br /> Soil Gas Survey <br /> A soil gas survey was conducted in the vicinity of the former tank pit and gasoline <br /> dispensing islands by Tracer Research Corporation on May 20, 1991 (Appendix A). <br /> The purpose of the soil gas survey was to qualitatively delineate the shallow vertical <br /> and lateral extent of volatile organic compounds in the shallow subsurface. <br /> A hydraulic hammer attached to the back of a one-ton van was used to push 314-inch- <br /> diameter hollow steel sample probes into the ground. After the probe was inserted to <br /> the desired depth, the above-ground end of the probe was connected to a vacuum <br /> pump. Before sampling, 2 to 5 liters of gas were evacuated with the pump in order to <br /> purge the volume of air within the probe. Then ten milliliters of gas were collected <br /> I and immediately analyzed using a gas chromatograph. The samples were analyzed for <br /> benzene, toluene, ethylbenzene, xylenes, and total volatile hydrocarbons. <br /> Seventeen soil gas locations in the vicinity of the former Disco tanks were sampled at <br /> depths between three and 13 feet bgs. The soil'gas locations are shown on Figure 2-1. <br /> Subsurface Soil Sampling <br /> j Figure 2-1 shows the seven soil borings that were drilled in the vicinity of the former <br /> ( Disco tanks. Soil samples were also collected during the installation of six groundwater <br /> SF031604NRP1003.51 2-1 <br />