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Risk Management Research
|Impacts of DNAPL Source Treatment: Experimental and Modeling Assessment of the
Benefits of Partial DNAPL Source Removal(EPA/600/R-09/096)
Once released into the subsurface environment, dense nonaqueous-phase liquids (DNAPLs) serve as long-term sources of groundwater contamination and are therefore a significant risk to water resources. Containment or removal are the two basic strategies that can be used in the management or restoration of a DNAPL-contaminated site.
Restoration can be pursued either through in situ destruction or extraction, and a number of aggressive DNAPL remediation techniques (e.g., alcohol or surfactant flushing, thermal treatment, air sparging, and chemical oxidation) have been developed for these purposes. Using the techniques, complete DNAPL removal may be possible at some sites, but because of technology limitations (such as the lack of reliable characterization and assessment approaches and financial restrictions) partial mass depletion may be the most likely end result of aggressive source treatment at most DNAPL contaminated sites. When it is not practical or economically feasible to achieve complete DNAPL mass depletion, it must be determined if the aggregate benefits of partial DNAPL mass depletion are sufficient to reduce risks to an acceptable level and if the costs associated with this partial depletion are justified by the benefits received.
This report summarizes research conducted to address these issues with the primary objective of the research being the development of a scientifically defensible approach for assessing the long term environmental impacts (benefits) of DNAPL removal from source zones. The technical approach used to achieve this objective was to:
A combination of field site demonstrations, laboratory experiments, and numerical and analytical modeling allowed evaluation of varied hydrogeological settings and remediation scenarios. Specifically, field demonstrations and laboratory experiments were used to investigate the relationships between aggressive source treatment, mass removal, and flux response. Numerical and analytical modeling was likewise used to investigate specific linkages between components, as well as to develop an overall framework encompassing all conceptual model components.
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