Abstract

Releases of dense non-aqueous phase liquids (DNAPLs) at a large number of public and private sites in the United States pose significant challenges in site remediation and long-term site management. Extensive contamination of ground water occurs as a result of significant dissolved plumes generated from these DNAPL source zones, which 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 defined here as the ground water region (volume) in which DNAPL is present as a separate phase, either as randomly distributed sub-zones at residual saturations or as "pools" of accumulation above confining units. The source zone 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 deployed at DNAPL sites. Several in situ technologies are available that can achieve substantial DNAPL source depletion, either by extraction or destruction. However, many site owners have been reluctant to implement aggressive source depletion technologies for several reasons:

• The risk of failure in meeting certain regulatory requirements (e.g., maximum contaminant levels in the source zone) after implementing a source depletion technology
• Uncertainties in site characterization (i.e., the location and amount of DNAPL in ground water at a site)
• Uncertainties in forecasting potential benefits and adverse impacts of partial source depletion
• Uncertainties in prediction of life cycle costs
• Uncertainties regarding the acceptability of alternative cleanup levels

At the majority of DNAPL sites, containment of the source zone and management of the dissolved plume for cost-effective risk reduction and regulatory compliance have been the strategies of choice.

Contact

David S. Burden

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