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Work Plan for Environmental Investigation May 18 , : 1989 <br /> Proposed ARCO Station Woodbridge, California AGS 39044-1W <br /> iv <br /> SOIL-VAPOR SURVEY <br /> The Applied GeoSystems soil-vapor probe is designed to obtain ' <br /> relative measurements of hydrocarbon concentrations in the soil <br /> by analyzing the soil vapor. Soil-vapor probes do not directly <br /> evaluate contamination levels because of the high number of <br /> variables associated with subsurface soil conditions. The <br /> proposed investigation uses a system in which a vapor sample ,'is <br /> 4: collected in a vial at the sample depth by a vacuum process. _The <br /> samples are then analyzed using a Photovac 10570 portable gas <br /> chromatograph. This instrument is a dual-column, manual- <br /> injection chromatograph with a photoionization detector that is <br /> sensitive to concentrations of hydrocarbon constituents in the, <br /> range of parts per billion. The analytical equipment proposed in <br /> this survey is housed in the Applied GeoSystems Mobile- Soil Vapor <br /> Laboratory, which provides a clean, temperature-controlled <br /> environment. The detection limit for the chromatograph was set <br />{w by verifying equal concentrations (1 part per million) benzene, <br /> toluene, and total xylene isomers, which are associated with the <br /> higher volatile phase of gasoline. Before analyzing the vapor <br /> r samples, the chromatograph is calibrated with a standard gas <br /> containing equal concentrations of benzene, toluene, and total. <br /> xylene isomers. <br /> 8 <br /> �j <br /> App/ied GeoSystems <br />