ishing returns” concept applied to the performance of active remedies for groundwater cleanup at complex sites?

This chapter provides a series of recommendations that, in the judgment of the Committee, will accelerate the transition of a site to one of three possible “end states,” where this term simply means a state where long-term management will be implemented if required. These “end states” are (1) closure in which unlimited use and unrestricted exposure levels have been attained (presumably no long-term management will be required at such sites, although even these sites can be subject to reopeners should conditions change); (2) long-term passive management (e.g., using MNA, NA, physical containment, PRBs, institutional controls, or some combination thereof), and (3) long-term active management (e.g., indefinite hydraulic containment using pump and treat or other active remedies requiring continuous operation). Complex sites under both passive and active long-term management could eventually transition to the closure end state, but the time frame extends many decades into the future.

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, taking risk reduction, life-cycle costs, and technical feasibility into account. The transition of a site to either passive or active long-term management must be accomplished in a manner that is transparent, reduces long-term risks to an acceptable level, and is practical and cost effective, among other goals.

SETTING THE STAGE

All complex contaminated groundwater sites will ultimately transition from investigation, through remedy selection, implementation, and operations, to long-term management and ultimately (without any time frame constraint) to attainment of unlimited use and unrestricted exposure goals. If these concentration levels have not been achieved after some reasonable time period, a site will require long-term monitoring and management under either passive remedies such as MNA or an active remedy such as pump and treat. The number of complex sites where achieving unlimited use and unrestricted exposure goals within a reasonable timeframe is unlikely is not known precisely, but as discussed in Chapter 2 is estimated to be in the range of 12,000 sites and may be much higher.

Over more than 30 years of remediation experience at contaminated groundwater sites following the passage of federal statutes (CERCLA and RCRA) and state regulations have shown that the duration of the cleanup process—from initial discovery of contamination to installation of “final” remedies (as opposed to interim actions designed to eliminate imminent



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