Releases of Dense Non-Aqueous Phase Liquids (DNAPLs) at a large number of public and private sector sites in the United States pose signifi cant challenges in site remediation and long-term site management. Extensive contamination of groundwater occurs as a result of signifi cant dissolved plumes generated from these DNAPL source zones that vary in size and complexity depending on site characteristics and DNAPL properties and distribution. Risk and liability management, consistent with regulatory compliance requirements, could involve remediation of the source zone as well as management of the dissolved plume. The source zone is defi ned here as the groundwater region (volume) in which DNAPL is present as a separate phase, either as randomly distributed sub-zones at residual saturations or 'pools' of accumulation above confi ning units and includes the volume of the aquifer that has had contact with free-phase DNAPL at one time, but where all of the DNAPL mass is now present only in the dissolved or sorbed phases or diffused into the matrix in fractured systems. Over the past two decades, innovations in site characterization and remediation technologies have been developed and deployed at DNAPL sites. Several in-situ technologies are available which can achieve substantial DNAPL source depletion either by extraction or destruction. However, because of the risk of failure in achieving certain regulatory targets after implementing a source-depletion technology (e.g., MCLs in the source zone), combined with uncertainties in site characterization (i.e., the location and amount of DNAPL in groundwater at a site), in forecasting potential benefi ts and adverse impacts of partial source depletion, in prediction of life cycle costs, and uncertainties regarding the acceptability of alternative clean-up levels, many site owners have been reluctant to undertake aggressive source-depletion technologies. Thus, at the majority of DNAPL sites, containment of the source zone and/or management of the dissolved plume for cost-effective risk/liability reduction and regulatory compliance have been the dominant strategies of choice.

Not distributed to depository libraries in paper format. "December 2003." Includes bibliographical references (pages 49-54). "EPA/600/R-03/143." EPA Contract Number: 68-C-02-092.