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Contaminants in the Subsurface: Source Zone Assessment and Remediation
Research Council’s (NRC) input to help determine the usefulness and applicability of source remediation as a cleanup strategy, including what can be accomplished by more aggressive technologies in terms of the total contaminant mass removed, risk reduction, and other metrics. Although chlorinated solvent DNAPLs are the primary focus of the report, chemical explosives are also considered in depth. The statement of task is provided below:
What is a meaningful definition of a “source” for the purpose of this study? How important is the source delineation step to the effectiveness of mass removal as a cleanup strategy? What tools or methods are available to delineate sources of organics contamination in complex sites? How should the uncertainty of these characterizations be quantified, in terms of both total mass and mass distribution?
What are the data and analytical requirements for determining the effectiveness of various source removal strategies, and how do these requirements change for different organic contaminant types or hydrogeologic environments? Effectiveness would consider the metrics of groundwater restoration, plume shrinkage and containment, mass removed, risk reduction, and life cycle site management costs.
What tools or techniques exist today, and what tools would need to be developed in the future, to help predict the likely benefits of source removal?
What would be the most important elements of a well-designed protocol to assist project managers in the field to assess the effects of source removal?
What can be concluded about the ability of source removal efforts to bring about substantial water quality benefits and to meet various cleanup goals? (For example, when can these efforts remove enough of the source to then rely on monitored natural attenuation?)
What have been the results of source removal activities at Army and other facilities to date? More generally, what can be said about the future use of source removal as a cleanup strategy and the specific technologies investigated during the study?
As a preliminary step, the NRC committee formed to conduct the study created a definition of “source” that would capture the essence of a source as a reservoir of contamination while making a distinction between the source zone and the plume of contaminated groundwater. In addition, to better capture the properties of chemical explosives, the definition encompasses pure solid sources, as shown below:
A source zone is a saturated or unsaturated subsurface zone containing hazardous substances, pollutants, or contaminants that acts as a reservoir