to meet the challenges facing complex sites. A comprehensive assessment of future research needs, undertaken at the federal level and involving coordination between federal agencies, would allow research funding to be allocated in an efficient and targeted manner.

BETTER DECISION MAKING DURING THE LONG-TERM MANAGEMENT OF COMPLEX GROUNDWATER CONTAMINATION SITES

The fact that at most complex groundwater sites drinking water standards will not be attained for decades should be more fully reflected in the decision-making process of existing cleanup programs. Thus, Chapter 7 provides a series of recommendations that will accelerate the transition of sites to one of three possible end states: (1) closure in which unlimited use and unrestricted exposure levels have been attained; (2) long-term passive management (e.g., using natural attenuation with or without monitoring, physical containment, permeable reactive barriers, and/or institutional controls), and (3) long-term active management (e.g., indefinite hydraulic containment using pump and treat). The acceleration of this transition to one of three end states is premised on using remedies that are fully protective of human health and the environment in combination with more rapid acceptance of alternative end states other than clean closure.

An alternative approach for better decision making at complex sites is shown in Figure 7-2. It includes the processes currently followed at all CERCLA facilities and at many complex sites regulated under other federal or state programs (RCRA or state Superfund), but it provides more detailed guidance for sites where recalcitrant contamination remains in place at levels above those allowing for unlimited use and unrestricted exposure. This alternative approach diverges from the status quo by requiring the explicit charting of risk reduction (as indicated by, e.g., contaminant concentration reduction) over time. Specifically, if data indicate that contaminant concentrations are approaching an asymptote, resulting in exponential increases in the unit cost of the remedy, then there is limited benefit in its continued operation. At this point of diminishing returns, it is appropriate to assess whether to take additional remedial action (if legally possible) or whether to transition to more passive long-term management.

If asymptotic conditions have occurred, a transition assessment is performed. The transition assessment evaluates each of the relevant alternatives (remedy modification or replacement, passive or active long-term management) based on the statutory and regulatory remedy selection criteria. This includes consideration of the risk from residual contamination in subsurface zones, life-cycle costs and the incremental costs compared to the level of risk reduction achieved, and the likely reaction of stakeholders.



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