Adsorption of chlorinated hydrocarbon vapors onto soil in the presence of water

Chlorinated solvents partition readily into the vapor-phase in unsaturated soils. Sorption from the vapor-phase affects both transport and recovery. The Brunauer-Emmett-Teller (BET) isotherm has been used to model adsorption of chlorinated solvent vapors; however, the BET equation is not accurate above reduced vapor pressures (p/p(sat)) of 0.35. New measurements of chlorinated alkane sorption have been used with a modified BET equation (MBET) to model the adsorption isotherms for five solvents. The MBET equation was found to fit experimental data accurately, especially at high reduced vapor pressures. The capacity of sandy loam soil to adsorb organic vapors decreased with increasing water content, probably due to less soil surface available for sorption. This effect is most evident at reduced vapor pressures greater than 0.5. Adsorption is related to distribution of excess surface energy, the number of molecular layers of water sorbed at the surface, and solute polarity. Results suggest that water films contain areas of high interfacial energy that interact with solute molecules via induced electrostatic forces.