Laboratory flow visualization experiments, using glass beads as the porous medium, were conducted to study air sparging, an innovative technology for subsurface contaminant remediation. The purpose of these experiments was to observe how air flows through saturated porous media and to obtain a basic understanding of air plume formation and medium heterogeneity effects. The experiments indicate that air flow occurring in discrete, stable channels is the most probable flow behavior in medium to fine grained water saturated porous media and that medium heterogeneity plays an important role in the development of air channels. Several simulated scales of heterogeneities, from pore to field, have been studied. The results suggest that air channel formation is sensitive to the various scales of heterogeneities. Site‐specific hydrogeologic settings have to be carefully reviewed before air sparging is applied to remediate sites contaminated by volatile organic compounds.

Dense nonaqueous phase liquids (DNAPLs), especially when present as trapped free-phase pools, are long-lived in the subsurface environment and extremely difficult to remove. Despite vigorous research efforts over the last two decades, all current DNAPL pool remediation strategies suffer from a combination of inefficiency, increased risk of contaminant spreading due to uncontrolled mobilization, and or high treatment costs. This work reports results from two novel strategies that use density-motivated approaches to mobilize DNAPLs. Experiments were conducted in onedimensional bench-scale columns and two-dimensional flow cells containing heterogeneous media and DNAPL pools to quantify removal efficiency. Results show that greater than 90% removal of the total DNAPL mass (including both pools and associated residuals) is possible. Further, the removal process is potentially safe and rapid: since it is a stable displacement strategy, it does not rely upon any mass transfer limited steps, and it can be applied using a total of less than one pore volume of flushing solution.

Although dense nonaqueous phase liquid (DNAPL) pools are an important source of groundwater contamination, little experimental data have been generated to develop a mature level of understanding of the problem, and few strategies specifically aimed at remediation have been advanced. We discuss the dominant importance of these features in subsurface systems, present novel two- and three-dimensional heterogeneous experimental systems, and show results from two evolving strategies for remediating DNAPL pools. These strategies involve the joint use of a dense brine barrier and controlled mobilization of trapped DNAPL using small-volume surfactant flushes. These experiments demonstrate a controlled, substantial reduction of entrapped DNAPL in both two- and three-dimensional heterogeneous domains, using less than a single pore volume of flushing solution in some cases.

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