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Report on Soil and Ground-Water Evaluation September 11, 1989 <br /> Proposed ARCO Station, Woodbridge, California - - AGS 39044-1 <br /> The soil-vapor probe locations are shown on the Concentration of BTX in Soil-vapor Map <br /> (Plate P-4). The maximum sample depth. is based on the depth to ground saturation <br /> because little or no vapor transport occurs below this depth.- The saturated zone varies in <br /> thickness depending on soil type but is generally assumed to -extend upward from the water <br /> table a few feet. Ground water was believed to be approximately 14 feet below ground <br /> surface at this site. Due to the nature of the subsurface material (dense, silty sand), the <br /> vapor probe could -not easily be hydraulically-driven, so a pilot hole was drilled to <br />(r approximately 10 feet after which the drive probe was pushed the remaining 2 feet. <br /> Description of Chromatograph and Method of Analysis <br /> A 0.10 milliliter (ml) vapor sample was.:-Withdrawn-from the sample vial using a 0.10 ml - <br /> syringe and injected into-a Photovac lOS70 portable- gas chromatograph for analysis. The <br /> instrument is a dual-column, manual-injection chromatograph equipped with a capillary <br /> column, an isothermal oven; and a photoionization detector that is sensitive . to <br /> concentrations of hydrocarbon constituents in the-range of parts per billion. <br /> The analytical equipment used in this survey is housed in Applied GeoSystems' Mobile Soil- <br /> Vapor Laboratory which provides a clean, temperature-controlled environment. The <br /> detection limit for the chromatograph was set by verifying linearity.and peak resolution <br /> with standard gas containing equal-concentrations (0.5 parts per million [ppm]) of benzene, <br /> ' Applied GeoSystems - <br />