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wia e.. a j i 1 � product or be adsorbed to the solid matrix and remain relatively immobile. Dissolved compounds will p tend to volatilize from the aqueous phase. The Henry's Law constant is the equilibrium ratio of a compound's concentration in the vapor phase to its concentration fi in the aqueous phase. The higher a compound's Henry's Law con 1 stant, the greater its tendency to volatilize from water into i air. Figure 3 .graphically illustrates the vapor pressure, aqueous solubilit Y.. and Henry s Law constants, and .their relationships, T for selected hydrocarbons typically found in gasoline. The I Henry's Law constant is approximated here as the ratio of vapor pressure to solubility. The Henry's Law constant is directly related to the tendency of ,p. compounds to volatilize as Opposed to solubilizing. Compounds ,s . with Henry's Law.constants greater than 0.'001 (atm' m3/m volatilize 'from water into air very rapidly ole} Y P Y (Lyman et al. 1982); those .with Henry's Lave constants greater than 0.01 (atm' m3/mole) are generally volatilized so rapidly that they are seldom. found in gasoline--contaminated ground water. it may Y be observed (Figure. .3) that tetraethyl'- lead (TEL) has an 'extremely low solubility and a relatively low vapor p pressure. As a result, ; r this constitvent 'would not ,')e expected to solubilize and migrate in ground water. and although its low vapor pressure would � . indicate slow volatilization,--its Henry's Law constant `indicates _ �a that it may be more ra idl volatilized than solubilized:. p� Y The s fate of TEL would be expected to be long-term binding to the ! � E soil. i t , On the basis of these properties it can be seen that associated if with 'any. ground water, soil, or free-product contamination is vapor phase contamination. The SVCA technique takes advantage of this, and through the collection and analysis of soil vapor h' EXXON9:84L Yi