The National Research Council proposes to undertake a study to improve hazardous waste management at problematic sites where the presence of recalcitrant and/or poorly accessible contaminants is preventing site closure. Nationally, there are thousands of such sites that require long-term management, although the exact number, the rate at which that number is growing, and the percentage that threaten public water supplies is unknown. The following questions would lead the work of an NRC committee convened to study site closure issues at contaminated subsurface sites.

• At how many sites does residual contamination remain such that site closure is not yet possible? At what percentage of these sites does residual contamination in groundwater threaten public water systems?

• What is technically feasible in terms of removing a certain percentage of the total contaminant mass? What percent removal would be needed to reach unrestricted use at most sites or to be able to extract groundwater and treat it for potable reuse? What should be the definition of “to the extent practicable” when discussing removing contaminant mass from the subsurface?

• How can progress of source remediation be measured to best correlate with the risks at a specific site? Recognizing the long term nature of many problems, what near-term endpoints for remediation might be established that would be beneficial and achievable? Are there regulatory barriers or inconsistencies that make it impossible to close sites even when the site-specific risk is negligible? How can they be overcome?

• The intractable nature of subsurface contamination suggests the need to discourage future contaminant releases, encourage the use of innovative and multiple technologies, and clean up sites sustainably. What progress has been made in these areas and what additional research is needed? For example, should decisions on cleanup consider greenhouse gas issues? Can natural attenuation really be relied upon when residual contamination includes relatively recalcitrant and/or immobile chemicals? How effective are long-term containment strategies, especially for inorganic contaminants? Is point-of-use treatment an appropriate strategy for managing subsurface contamination?

• How can limited financial resources be spent, while taking into consideration the concerns of stakeholders? Should life cycle assessment become a standard component of the decision process? How can a greater understanding of the limited current (but not necessarily future) potential to restore groundwater be communicated to the public? Are their lessons to be learned from the nation’s experience with long-term management of radionuclides that could be applied to sites with more common types of residual contamination?