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R <br /> Most fuel hyrocarbon liquids consist of a complex mixture of many <br /> compounds, each with its own physicochemical properties . The <br /> constituents found in ground water located beneath a layer of <br /> floating hydrocarbon are generally less hydrophobic and are <br /> generally found in concentrations proportional to the hydro- <br /> carbon/water partition coefficient ( i .e. , the relative solubility <br /> of a given compound in the bulk hydrocarbon to its solubility in <br /> water ) and to their percent composition in the original product. <br /> Hydrocarbon liquids will also volatilize into the air-or gas-- <br /> filled soil interstices once in subsurface soils. volatilization <br /> is largely a function of Raoults ' s Law, which describes the <br /> relationship between the tendency of a compound to remain in <br /> solution in the free product and its tendency to volatilize. In <br /> general, compounds with higher vapor pressures and higher <br /> Raoults ' s Law constants are found in relatively greater concen- <br /> trations in the soil vapor . The natures of the hydrocarbon mix- <br /> tures, internis of specific component mixtures, in either the <br /> aqueous or vapor phase, are distinctly different from each other <br /> and form the original product. That is, the more hydrophillic <br /> constituents will be more likely to move into ground water and <br /> the more volatile compounds will be more likely to move into the <br /> vapor phase. The compounds that are both, less volatile, and <br /> more hydrophobic, will be more likely to remain in the free <br /> product or be adsorbed to soils . <br /> Hydrocarbons not remaining in the free product will partition <br /> into either ground water or soil vapor and migrate as the result <br /> of a variety of interacting forces . In ground water, hydrocar- <br /> bons will migrate with the ground-water flow, interacting with <br /> the rock or soil geological medium. As the hydrocarbons pass <br /> through the soil , organic constituents in the soil interact with <br /> the hydrocarbons and some are adsorbed or bound to soil particle <br /> surface The result of this adsorption is a net retardation in <br /> the migration velocity of those compounds relatige tc that of the <br /> ground water in which they are dissolved (The process is <br /> • analogous to laboratory chromatography the compound with the <br /> 2 <br />