Attenuation Processes for Metals and Radionuclides

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Until recently, there has been little regulatory guidance to support attenuation-based remedies for radionuclide and metals contamination. This lack has contributed to inconsistent application of those remedies and generally discouraged their consideration. The net result is that many sites face intractable closure problems. EPA recently issued the first two volumes of technical guidance that specifically address monitored natural attenuation (MNA) of inorganic contaminants. A third volume (anticipated in late 2010) will address MNA of specific radionuclides. These new documents provide technical information related to the dominant attenuation mechanisms and methods for characterization and evaluation of specific inorganic contaminants and radionuclides.

Attenuation-based remedies for metals and long-lived radionuclides rely primarily on immobilization of contaminants as stable and/or nontoxic species. This stabilization and toxicity reduction can result from natural processes, geochemical gradients, or biogeochemical manipulation. Except for a few radionuclides, the original contaminant remains in the subsurface so that documentation of the sustainability or permanence of stabilization and detoxification is crucial to assessing performance. Another challenge in applying the existing and emerging guidance is the need to simultaneously address multiple contaminants at a target site.

Formed in 2008, ITRC's Natural Attenuation Processes for Metals and Radionuclides (APMR) Team is in a unique position to develop a framework to facilitate implementation of the new EPA guidance for MNA of metals and radionuclides. This framework provides a consistent basis for states, stakeholders, federal agencies, and site owners to evaluate and implement attenuation-based remedies. The project encompasses a process that encourages regulatory cooperation and sharing of successful technological approaches. In December 2010, the APMR Team released a technical and regulatory guidance document entitled A Decision Framework for Applying Monitored Natural Attenuation Processes to Metals and Radionuclides in Groundwater. The companion Internet-based training opportunities are scheduled to roll out in 2011.