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Report of Soil Vapor Survey January 12, 1989 <br /> UNOCAL Station No. 6981, Stockton, California AGS 38032-2V <br /> relative concentrations and the lateral extant of hydrocarbon <br /> contamination as vapor in soil has been found to correlate to <br /> those of ground water (Devitt et al. , 1987) ; therefore, a soil <br /> vapor survey can be used to evaluate the lateral extent of <br /> hydrocarbon contamination in both the soil and ground water. <br /> Application of the soil vapor survey is based on the tendency of <br /> hydrocarbons with low molecular weights to volatilize and migrate <br /> through the pore spaces of soil. Hydrocarbon <br /> product can migrate <br /> through the subsurface as free product or as dissolved product in <br /> water and act :as a source of hydrocarbon vapor in the soil poxes. <br /> ' Residual product trapped or bound within pore spaces also acts as <br /> a source of hydrocarbon vapor. variables that influence <br /> hydrocarbon movement in the soil include the physical and <br /> chemical properties of the organic contaminants, properties of <br /> the unsaturated zone, and hydrogeologic properties of the site. <br /> Site--specific parameters may include the vapor pressure, water <br /> solubility, and concentration of the chemical; the porosity, <br /> moisture content, and organic content of the site soil; and the <br /> flow direction and velocity of the ground water. <br /> 3 <br /> ,4lal®Ileof 4GB4S. teIns <br />