Chlorinated solvent contamination is widespread across the U.S. Department of Energy (DOE) complex and other industrial facilities. Because of the physical properties of dense nonaqueous-phase liquids (DNAPLs), current treatment technologies are generally incapable of completely removing contamination from the source area. Incomplete removal means that the residual DNAPL will persist as a long-term source of groundwater contamination. When DNALPs occur in the subsurface, they resist remediation, owing to low water volubility, high viscosity and interracial tension, and microbial recalcitrance. Because of their high density and polarity, they are usually found sorbed to aquifer solids or in pools on impermeable materials. Surfactants have been used with some success to reduce interracial tension between the aqueous and organic phases and improve volubility of DNAPLs. However, surfactants are expensive and toxic and exhibit an oxygen demand. An alternative is the use of dissolved humic acids in improving DNAPL mobilization and solubilization. Humic acids, a. natural form of organic carbon, are abundant, inexpensive, and nontoxic; biodegrade slowly (low oxygen demand,2587 ); and have excellent mobilization properties. The present work is to establish the feasibility of using humates for enhancing DNAPL remediation.