In situ remediation of aquifers contaminated with dense nonaqueous phase liquids by chemically enhanced solubilization

Chemically enhanced solubilization (CES) is an advanced variant of pump‐andtreat that results in more effective and more rapid remediation of groundwater contaminated with organic solvents and other dense nonaqueous‐phase liquids (DNAPLs). Attempts to remediate DNAPL‐contaminated groundwater by pump‐and‐treat have generally not been successful, due to the low aqueous solubility of most DNAPLs. Regions of undissolved, organic liquids slowly release additional contamination to surrounding groundwater, in effect acting as in situ sources of contamination and hindering the progress of remediation attempts. Cleaning up an aquifer can take many decades or more of pump‐and‐treat. CES accelerates pump‐and‐treat by using surfactants at low concentration to increase the solubility of organic contaminants by up to three orders of magnitude, while maintaining hydraulic control. The surfactants are chosen to maximize contaminant solubilization while minimizing decreases in the DNAPL/ water interfacial tension in order to prevent mobilization of DNAPL to uncontaminated regions. The surfactants are also selected to be nontoxic and biodegradable (many are U.S. Food and Drug Administration‐ (FDA‐) approved food additives). After the contaminants have been solubilized, they are pumped to the surface and treated by air stripping and other methods as in traditional pump‐and‐treat operations. CES has had extensive laboratory development and is now being field tested at three sites. The first field test is at Canadian Forces Base Borden, a military facility in Ontario, Canada. The field test involves the controlled contamination of a shallow sand aquifer with approximately 240 L of tetrachloroethylene (PCE). CES increased the contaminant concentration in the extracted water to over 10,000 ppm of PCE, compared with an aqueous solubility of 200 ppm. At latest report, more than 80% of the residual PCE has been removed. A second field test is currently in preparation at a chlorinated solvent manufacturing facility in Texas and a third at a DOE site with PCE, 1,1,1‐trichloroethane (TCA), and trichloroethylene (TCE) contamination.