Gasoline vapor transport through a high-water-content soil

The diffusive transport of gasoline vapors in a fine-grained, high-water-conent soil was examined in a combined field, laboratory and modeling study. Subsurface vapor concentrations of a variety of gasoline-derived compounds were monitored for one year at a gasoline service station. Effective diffusion coefficients were measured in the laboratory using soil columns. Data indicate that diffusive transport in the soil is quite slow. Numerical modeling, using the parameters determined in the field and laboratory, suggests that the vapors would spread only a few meters per year. The implications are that vapor-phase monitoring for gasoline leaks in such soils will not allow rapid detection and that even small releases of product will cause high vapor concentrations for prolonged time periods.