A major issue in the cleanup of this country's nuclear weapons complex is how to dispose of the radioactive waste resulting primarily from the chemical processing operations for the recovery of plutonium and other defense strategic nuclear materials. The wastes are stored in hundreds of large underground tanks at four U.S. Department of Energy (DOE) sites throughout the United States. The tanks contain hundreds of thousands of cubic meters of radioactive and hazardous waste. Most of it is high-level waste (HLW), some of it is transuranic (TRU) or low- level waste (LLW), and essentially all containing significant amounts of chemicals deemed hazardous. Of the 278 tanks involved, about 70 are known or assumed to have leaked some of their contents to the environment. The remediation of the tanks and their contents requires the development of new technologies to enable cleanup and minimize costs while meeting various health, safety, and environmental objectives. While DOE has a process based on stakeholder participation for screening and formulating technology needs, it lacks transparency (in terms of being apparent to all concerned decision makers and other interested parties) and a systematic basis (in terms of identifying end states for the contaminants and developing pathways to these states from the present conditions). An End State Methodology for Identifying Technology Needs for Environmental Management, with an Example from the Hanford Site Tanks describes an approach for identifying technology development needs that is both systematic and transparent to enhance the cleanup and remediation of the tank contents and their sites. The authoring committee believes that the recommended end state based approach can be applied to DOE waste management in general, not just to waste in tanks. The approach is illustrated through an example based on the tanks at the DOE Hanford Site in southeastern Washington state, the location of some 60 percent by volume of the tank waste residues.

The Department of Energy's Office of Environmental Management's (EM) mission is the safe cleanup of sites associated with the government-led development of nuclear weapons and nuclear energy. While many of these legacy sites have completed cleanup, the largest and most complex sites have not been fully remediated. The cleanup of these sites is proceeding under legally enforceable agreements with timelines for hundreds of milestones. EM is reviewing alternative approaches to increase effectiveness and improve cost efficiencies of its cleanup activities, especially for sites that will have residual contamination when active cleanup is complete. This report is the summary of two workshops convened in October 2013 and January 2014 on best practices for risk-informed remedy selection, closure, and post-closure control of radioactive and chemically contaminated sites that present significant difficulty for remediation to unrestricted release. The workshop series aimed to explore best practices that promote effective, risk-informed decision making and future opportunities to improve remediation approaches and practices.In the Workshop #1 section of Best Practices for Risk-Informed Decision Making Regarding Contaminated Sites, the report examines holistic approaches for remediating sites with multiple contaminant sources and post-closure uses, and approaches for incorporating a sustainability framework into decision making regarding site remediation, closure, and post-closure control. In Workshop #2, the report focuses on post-closure controls, assessment of long-term performance of site remedies, and best practices for risk-based remediation decisions.