Date: 17 May 2010

DNAPL Site Characterization Issues at Chlorinated Solvent Sites

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Abstract

Past releases of chlorinated solvents generally occurred as dense nonaqueous phase liquids (DNAPLs). Because DNAPLs are heavier than water and are sparingly soluble, they pose difficult characterization, remediation and long-term management challenges. At such sites, a distinction is made between the source zone, which includes portions of the subsurface where DNAPL is or was present as a separate phase, and the downgradient plume of dissolved contamination resulting from groundwater flow through the source zone. Site management frequently involves attempting to contain or deplete contamination in both of these areas. During the past two decades, several promising in situ technologies (e.g., chemical oxidation, thermal extraction and cosolvent/surfactant flushing) have been applied at many sites to remove or destroy contaminants in DNAPL source zones. Yet the U.S. Environmental Protection Agency (USEPA) Expert Panel on DNAPL Remediation (USEPA, 2003) concluded that: