Complex groundwater sites present significant technical challenges in achieving cleanup goals within a reasonable timeframe due to the nature and extent of contamination, geologic setting (e.g., fractured bedrock or low permeability formations), stringent cleanup goals, and lack of effective remedial options. Remedial Project Managers (RPMs) apply appropriate adaptive site management strategies and risk management approaches for addressing these complex groundwater sites.
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Complex groundwater sites carry high levels of uncertainty in achieving Response Complete (RC). Challenges may result from the site setting, nature and extent of contamination, technology limitations, or other non-technical challenges from evolving regulations, political interest, and/or public visibility. Specific examples of challenging site conditions include large-scale or deep plumes, complex geology or hydrogeology (e.g., fractured rock or low permeability formations including matrix diffusion), certain types of contamination (e.g., dense non-aqueous phase liquid [DNAPL] source zones), and adverse geochemical conditions.
A comprehensive risk-based approach can be protective of human health and the environment at these sites. In some cases, the RPM consider if risk management (e.g., institutional controls and containment) may be the most effective method of eliminating exposure pathways at complex sites. The Interstate Technology and Regulatory Council (ITRC) has recommended an adaptive site management approach for complex sites. Adaptive site management is a comprehensive, flexible, and iterative process that is well suited for sites where there is significant uncertainty in remedy performance. This process includes the establishment of interim objectives and long-term site objectives that consider both technical and non-technical challenges. Periodic adjustment of the remedial approach may involve transitioning from aggressive source and/or containment technologies to passive treatment or monitored natural attenuation over time (often referred to as a “treatment train”). RPMs plan for evaluations to actively track remedy progress and to improve the timeliness of remedy optimization or technology transitions. More information can be found in ITRC Remediation Management of Complex Sites.
Various risk management approaches can be incorporated as components of the adaptive site management framework. Approaches can include applicable or relevant and appropriate requirement (ARAR) waivers, technical impracticability (TI) waivers, state designations (e.g., plume management zones), alternate concentration limits (ACLs), and groundwater reclassification. For example, alternative endpoints are formal designations for alternate remedial goals that are permitted by regulations. These alternate remedial goals allow cleanup decisions to be based on site-specific exposure and risk, rather than defaulting to a commonly applied value such as a maximum contaminant level (MCL) where groundwater does not serve as a drinking water source. Adaptive approaches can also be used to meet traditional endpoints over the long term such as monitored natural attenuation (MNA) over extended timeframes and low-threat or risk-based closure. More information on alternative endpoints, TI waivers, ACLs, and other risk management approaches can be found in Chapter 8 of the Department of the Navy (DON) Environmental Restoration Program (ERP) Manual.