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' w <br /> Work Plan for Environmental Investigation June 21, 1989 <br /> Waterfront Redevelopment, Stockton, California AGS 39048-1W <br /> concentrations can be delineated across the site. The proposed <br /> investigation uses a system in which a vapor sample is collected <br /> in a vial at the sample depth by a vacuum process. The samples <br /> are then analyzed using a Photovac lOS70 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 in this <br /> 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 /> 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 /> samples, the chromatograph is calibrated with a standard gas <br /> containing equal concentrations of benzene, toluene, and total <br /> xylene isomers. <br /> Equipment used to sample soil vapor includes a hardened steel <br /> drive-tip, a downhole sampling assembly with vacuum vials, steel <br /> probe rods with an outside diameter of 1. 75 inches, and a driving <br /> unit. The vapor probe is pushed or driven to the desired depth, <br /> and the sampling assembly containing an evacuated sample vial is <br /> 9 <br /> AppIleal GeoSystems <br />