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December 2, 1997 • <br /> Pa,e 4 <br /> dispenser island. Soil boring data indicated that hydrocarbon impact may extend to <br /> depths of greater than 50 feet in some areas such as Boring B-11. <br /> Task 2.1 - Borings. PACIFIC proposes to install three confirmation soil borings, at the <br /> locations shown on Figure 2, to comply with the PHS/EHD request. The borings will be <br /> drilled to a depth of 60 feet using hollow-stem auger drilling equipment. Soil samples <br /> will be obtained at 5-foot depth inrervals. All soil samples will be analyzed in the field <br /> with a photo-ionization detector (PID) for relative characterization of hydrocarbon <br /> concentrations, and selected samples will be submitted for confirmation laboratory <br /> analysis of hydrocarbons and other selected compounds. All waste soils will be properly <br /> disposed of off site. <br /> Task 2.2 - Laboratory.Analysis. All soil samples from the borings will be sent to a <br /> California State-certified laboratory for analysis of total purgeable petroleum hydrocar- <br /> bons calculated as gasoline (TPPH-g) by EPA Method 8015 (modified), and benzene, <br /> toluene, ethylbenzene, and xylenes by EPA Method 8020. <br /> Task 3 - Sparge Wells <br /> To comply with the PHS/EHD request, one of the confirmation soil borings described in <br /> Task 2 will be converted to a sparge well by the installation of 2-inch diameter PVC <br /> casing screened within the saturated zone in the 40- to 60-foot depth interval. Well <br /> construction will be completed in accordance with the procedures described under <br /> Task 1.2. The well will be equipped with sparge assembly and a surface air source. The <br /> impact of air entry into the saturated zone will be monitored in nearby existing vapor <br /> extraction wells by measurement of changes in influent hydrocarbon concentrations. <br /> Task 4 - Vapor Extraction Radius of Influence <br /> Initial testing by Resna indicated vapor extraction wells would have a radius of influence <br /> of approximately 50 feet. In order to reevaluate the effectiveness of the system, GSI <br /> evaluated the radius of influence in May and June 1996. Their testing concluded that the <br /> radius of influence averaged 60 feet. Based on the similarity in the two test results, it <br /> appears that the radius of influence for the SVE system has been adequately character- <br /> ized. However, to comply with the PHS/EHD request, a third vapor extraction test will <br /> be performed using existing wells to detennine the area of the radius of influence of the <br /> SVE system. One existing vapor extraction well will be selected for extraction while <br /> changes in pressure are monitored in surrounding vapor wells. The test will be <br /> conducted for 8 hours. <br /> sI r 1657.,%%srocr LDoc <br />