Nonaqueous phase liquid dissolution and soil organic matter sorption in porous media: review of system similarities

We examine similarities in constraints to mass transfer of hydrophobic organic compounds (HOCs) between the aqueous and various organic phases in porous media at the grain scale. Published research and data are reviewed regarding equilibrium coefficients and first-order rate constants for mass transfer of HOCs between water and natural organic matter present in various geosorbents (e.g., soils, sediments, and aquifer solids), and several oils (petroleum products, decane, and coal tar). We propose how these equilibrium and mass-transfer coefficients can be estimated by methods common to all organic phases. Equilibrium coefficients can be reliably estimated using Raoult's law. First-order rate constants obtained from extensive literature data appear to be dependent on aqueous-phase diffusion and duration of exposure (or contact). The aqueous diffusion domain may be either an interfacial film (for low viscosity oil ganglia) or a retarded immobile water zone (for geosorbents).