Predicting the Effect of Moisture on Vapor-Phase Sorption of Volatile Organic Compounds to Soils

Sorption from the vapor phase is an important factor controlling the transport of volatile organic compounds (VOCs) in the unsaturated zone. Accurate description of sorption from the vapor phase to soil in the unsaturated zone therefore is intrinsic to predicting the ultimate fate of contaminants. Vapor-phase sorption of several VOCs onto seven soils at oven-dried, air-dried, typical field moisture and water-saturated conditions was measured using a batch-equilibrium headspace method. An equilibrium partitioning model was developed to predict the effect of soil moisture content on vapor-phase sorption. The model was based on the soil pore-size distribution and BET isotherm sorption parameters under oven-dried and water-saturated conditions. The model was shown to accurately predict observed experimental results.