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__ _ A _ g <br /> ReM <br /> potential drinking water source and several city and private <br /> wells exi?t within a mile radius of the site. These wells are <br /> reportedly in use daily (Cox 1988) . <br /> 1.4 PRINCIPLES AND APPLICATION OF SOIL VAPOR CONTAMINANT <br /> i ASSESSMENT <br /> The soil vapor survey, or SVGA, technique takes advantage of the <br /> behavior of hydrocarbon mixtures and the physicochemical proper--. <br /> ;. ties of the individual components in the subsurface. Following a <br /> . �i subsurface gasoline release, free product will migrate downwards <br /> towards the ground water, some of the gasoline will volatilize, F <br /> and some will adsorb to the. soils. In the case of a spill of: E <br /> sufficient volume to exceed the soil binding capacity, free <br /> liquid will reach ground water, at which point it will float: and <br /> �. F-� =.ay .begin to vaporize and solubilize. <br /> w �f <br /> r <br /> -/ Like most hydrocarbon liquids, gasoline is a complex mixture of <br /> many compounds, each with its own physicochemical properties. <br /> .: The contaminants found in. ground water .located beneath a layer of <br /> i <br /> (j floating hydrocarbon aze generally less hydrophobic 'and are <br /> L° generally found in concentrations proportional to .the hydro <br /> i� carbon/water partition coefficient (i.e., the relative solubility <br /> �, I... of a given compour_d in the bulk hydrocarbon to its solubility in <br /> water) and to their percent composition in the gasoline. It may <br /> be .noted that concentration of total benzene, toluene,. and <br /> xylenes. in product-saturated water may exceed 10-20. mg/L (API <br /> . ?. 1985a) <br /> f Hydrocarbons will also volatilize into the air or gasfilled <br /> soilinterstices. Volatilization is largely a function of. vapor , <br /> pressure. The natures of the contaminant mixtures, in terms of <br /> specific component mixtures,. in either the aqueous or vapor <br /> phase, are distinctly different from each otherand from the <br /> ~. . <br /> e # <br /> gasoline.. That is, the jr�ore hydrophilic hyd��ocarbons will be <br /> more likely to move into ground water, while the more volatile <br /> EXXON9:84L 3 <br /> �k <br />