DECISION FRAMEWORK FOR APPLYING ATTENUATION PROCESSES TO METALS AND RADIONUCLIDES

Until recently, there has been little regulatory guidance to support attenuation–based remedies for groundwater contaminated with metals and radionuclides. This has contributed to inconsistent application of those remedies and generally discouraged their consideration. The net result is that many sites face intractable closure problems. The U.S. Environmental Protection Agency (EPA) recently issued a three-volume technical guidance set that specifically address monitored natural attenuation (MNA) of inorganic (i.e., radionuclide and non-radionuclide) contaminants. These new documents provide technical information related to the dominant attenuation mechanisms, as well as 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, as is often the case in actual practice.

The Interstate Technology & Regulatory Council (ITRC) has developed a technical and regulatory guidance to facilitate implementation of the new EPA guidance for MNA of metals and radionuclides. A decision framework in this guidance document provides a consistent basis for states, stakeholders, federal agencies, and site owners to evaluate and implement attenuation-based remedies. Additionally, an enhanced attenuation strategy will support instances where actions may be needed to support long-term sustainability of the MNA mechanisms. Current federal and state regulatory policy and guidance is summarized and factors crucial to regulatory acceptance are presented. The outcome of these efforts is a process that will encourage regulatory cooperation and expedite cleanup.