Remediation of DNAPL-Contaminated Subsurface Systems Using Density-Motivated Mobilization

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 one-dimensional 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.