Quantifying Gas Phase Dispersion in Soil Media

Hydrocarbon contamination of unsaturated soils has been a serious environmental problem for decades. Two of the most common methods of remediating these sites are soil vapour extraction (SVE) and bioventing. Predictive models have been developed for the SVE and bioventing processes in order to estimate mass transfer coefficients for experimental systems and clean up times for field sites. These techniques are typically modeled using the advection-dispersion system of equations. Unfortunately, many of the required modeling parameters are still poorly understood or unavailable. Modellers of the process either utilize correlations to estimate dispersion coefficients or neglect dispersion altogether. Previous studies have demonstrated that uniform packed bed correlations can seriously underestimate dispersion occurring in non-uniform unsaturated soils under dry and moist conditions. Currently, very little literature information is available regarding gas phase dispersion in unsaturated soils. Most experimental studies aimed at measuring dispersion have used disturbed soils, manipulated to some degree from field conditions. Therefore, dispersion estimates are not a true representation of actual field sites. Accordingly, research has been conducted on the development of a laboratory technique that can measure dispersion in both disturbed and undisturbed soils under unsaturated conditions. The apparatus has been developed and has been used to measure dispersion in disturbed soils. These results and the application to field sites will be discussed.