Relations between behavior of gaseous VOCs in unsaturated zone and gas adsorption to soil

The soil vapor extraction (SVE) is one of in situ remediation techniques, and the behavior of gaseous volatile organic compounds (VOCs) plays an important role of the purification of underground pollution and groundwater contamination. Numerical simulations, including the delay of a gas transport, will allow evaluating the gas behavior in unsaturated zone. The factors related with the delay depend on mainly the dissolution from a gas to moisture, the adsorption from moisture to a soil, and the adsorption from a gas to a soil directly. The retardation coefficient is formulated by including these three factors, and some laboratory experiments are performed about the adsorption from a gas to a soil and the retardation coefficient. The result of these experiments is that kind, diameter and specific surface area of soils relate with the adsorption coefficient, within the limit of this investigation. Two-dimensional numerical simulations under some boundary conditions make clear the velocity profile, the concentration distribution of gaseous VOCs in unsaturated zone at the extraction, and the relation between the condition of the ground surface and the mass of removed contaminants.