Sxi

where:

Pv = vapor pressure of the chemical in mmHg

Mw = molecular weight of the chemical

S = solubility in mg/l

Published texts report Henry's law constant in various units such as atm-m3/mole, atm-cm3/g, or dimensionless depending on the units used for Ca and Cw. Table 9.12.5 lists Henry's constants for several organic chemicals. According to Lyman and others (1982), if H is less than 10~7 atm-m3/mole, the substance has a low volatility. If H is less than 10~5 but greater than 10~7 atm-m3/mole, the substance volatilizes slowly. However, the volatilization becomes an important transfer mechanism when H is greater than 10~5 atm-m3/mole.

Several soil characteristics affect the volatilization of organic chemicals in groundwater. Volatilization decreases as the soil porosity decreases or as the soil water content increases. Soils with high clay content tend to have a high water content and hence low volatilization (Jury 1986).

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