The Department of Defense (DoD) has many complex sites where remedial time frames to achieve maximum contaminant levels (MCLs) or background concentrations in groundwater throughout the aquifer are prohibitive. In the presence of dense nonaqueous phase liquid (DNAPL), pump-and-treat and other technologies targeting dissolved-phase contamination in hydraulic contact with DNAPL are limited by DNAPL dissolution time frames, which can be on the order of hundreds of years. In geologic settings where transmissive zones are a small fraction of the aquifer’s total volume (e.g., fractured rock settings, sites with interbedded low permeability zones), matrix diffusion and matrix storage also can extend cleanup time frames. Aquifer restoration to drinking water standards at sites with these complex geologic and contaminant characteristics has rarely been achieved, and attempts to reach MCLs or background concentrations throughout the aquifer are projected to cost DoD millions of dollars and other resources while achieving little practical or measurable benefits. At complex sites like these, alternative endpoints and approaches can be beneficial or even necessary.
Alternative endpoints are formal designations for alternative final remedial goals that are permitted by regulations and are protective of human health and the environment. Examples of alternative endpoints and approaches include applicable or relevant and appropriate requirement (ARAR) waivers, alternate concentration limits (ACLs), adaptive site management approaches, and the use of passive remedies over long time frames.
The objective of this project was to provide environmental managers and regulators at DoD sites with tools, metrics, and information needed to evaluate alternative endpoints for groundwater remediation at complex sites.
A survey of sites where alternative endpoints and metrics have been incorporated into remedies was conducted. The survey results are presented in the Final Report, which is intended to provide DoD site managers and other stakeholders an overview of alternative endpoints and approaches to address cleanup complexities or challenges. The report covers how sites have formulated alternative endpoints and metrics and how they have documented their decisions. The alternative endpoints and approaches highlighted in the report include the following:
- Technical impracticability (TI) waivers
- Other ARAR waivers
- Groundwater management/containment zones (CZ)
- Groundwater reclassification/classification exemptions
- Monitored natural attenuation (MNA) over long time frames
- Adaptive site management
- Remediation to the extent practicable.
A number of workshops also were conducted to stimulate discussions on evaluating alternative endpoints for groundwater cleanup, promote knowledge and technology transfer, and help DoD and regulators recognize opportunities for alternative endpoints and metrics at complex sites.
Since complex sites frequently constitute the majority of a cleanup program budget, alternative remedial endpoints may lead to significant cost savings while providing the same level of protection to human health and the environment. Other benefits include the ability to move DoD sites forward in the remedial process towards site closure and the latitude to define realistic performance objectives for source reduction or containment technologies.