Gas-phase transport and sorption of benzene in soil

To better understand the transport of gaseous organic compounds through soil near buildings and under high soil gas flow rates in remediation processes, we have studied benzene equilibrium partitioning and sorption kinetics on low organic content soil grains and transport through soil columns under dry and slightly moist conditions. Sorption capacities and rates of adsorption and desorption were measured using the differential adsorption bed technique. Dry soil sorption equilibrium is well described by the nonlinear Freundlich isotherm. As the relative humidity (RH) increases from zero to 33%, the isotherm gradually changes fromnonlinear to linear and the soil sorption capacity decreases. For dry soil, adsorption occurs more rapidly than desorption; formoist soil, adsorption and desorption kinetics are significantly faster and symmetric. The relative rates of adsorption and desorption are related to the shape of the equilibrium isotherm; at a given RH, the isotherm was successfully inferred using an intragrain diffusion model and the results of a single kinetic experiment. This intragrain model was coupled to an advectiondiffusion- sorption equation to predict transport through a soil column. Using the parameters extracted from kinetic experiments, column breakthrough curves were successfully simulated over a range of flow conditions.