Influence of Air−Water Interfacial Adsorption and Gas-Phase Partitioning on the Transport of Organic Chemicals in Unsaturated Porous Media

Abstract

We investigated in laboratory column experiments, the aqueous-phase transport of four n-alcohols (n-hexanol−n-nonanol), three chlorinated aromatic compounds (chlorobenzene, o-dichlorobenzene, and o-chlorophenol), and two alkylbenzenes (ethylbenzene and p-xylene) in a water-unsaturated porous medium (sand). The influence of gas-phase partitioning and interfacial adsorption on solute retardation during steady unsaturated water flow was evalu ated over a range of water contents. Air−water interfacial adsorption was a significant factor for the retardation of n-alcohols. For example, nearly 90% of the measured retardation of n-nonanol could be attributed to interfacial adsorption at a water saturation of 34%. Aromatic compounds used in this study were not significantly affected by adsorption at the air−water interface because of both low air−water interfacial area (0−50 cm2/cm3) generated in the unsaturated porous medium and the small interfacial−adsorption coefficients. Instead, gas-phase partitioning was th...