PNNL

Cleanup of waste from World War II and the Cold War era at the Hanford Site’s Central Plateau has been underway for more than 30 years. The south-central area of Washington state bordering the Columbia River contains hundreds of contaminated soil sites posing a risk to groundwater.

The Department of Energy has prioritized cleanup of the Central Plateau. It’s a task complicated by large-scale ground water plumes as well as a contaminated, thick vadose zone—the Earth subsurface that’s above the groundwater table.

As the cleanup unfolds, management decisions are made that will affect near- and long-term actions. Typically, a phased process guides cleanup methods and management of contaminated sites. In this traditional approach, changes to cleanup action plans, even if responding to real-time data that differs from information used to approve a cleanup plan in the first place, must be vetted through a time-consuming process of describing implementation plan changes and getting reviews and approvals.

However, an equally formal but more flexible procedure may be better suited to cleanup at the Central Plateau, according to scientists at Pacific Northwest National Laboratory (PNNL) in Richland. They propose an “adaptive site management” (ASM) strategy to provide more flexibility for timely decision-making in a manner approved by regulators.

“ASM has the potential to expedite cleanup for the Central Plateau area at Hanford through a planned and systematic approach for reducing uncertainty with targeted characterization activities, while continuing remediation activities that advance cleanup for key risk-driving contaminants,” says the study, “Adaptive Site Management Strategies for the Hanford Central Plateau Groundwater.”

The uncertainty associated with contaminant behavior and distribution in the subsurface makes the Hanford Site ideal  for the adoption of ASM practices, said Inci Demirkanli, a PNNL environmental engineer and senior scientist who is the study's co-author and serves as Deputy Director of Environmental Remediation Applications for the Center for the Remediation of Complex Sites (RemPlex).

Furthermore, many of the cleanup actions on the Central Plateau are still early in the remediation decision process, and overall cleanup efforts are estimated to last decades and cost tens of billions of dollars in life cycle schedule and budget

Hanford cleanup follows the process described by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), otherwise known as Superfund. In some cases at Hanford, the Resource Conservation and Recovery Act (RCRA) may be the governing regulatory framework. ASM could be used for decision making under either regulatory context, Demirkanli said.

 “Adaptive site management would allow site managers to recognize and adapt to site uncertainties and changing conditions about their cleanup decisions,” said Demirkanli. “In an iterative, stepwise fashion, which is a key to ASM, you try to tackle your major uncertainties and reduce those uncertainties. That way, you generate information and you re-evaluate your cleanup decisions as the remedy progresses.”

The study says ASM’s flexible and iterative method consisting of multiple intermediate steps is needed to manage the uncertainty inherent to the Central Plateau contamination. The study calls for three key steps to implement ASM:

1. Identify site objectives that are consistent with the overall Hanford cleanup goals and that support the development of a long-term management approach,
2. Set interim goals that provide quantifiable, stepwise progress for achieving site objectives, and
3. Establish remedial actions that address key uncertainties and data gaps.

“In essence, what we are calling for is targeted information collection/evaluations to address key uncertainties and the ability to adapt to new information,” said Demirkanli. “Adaptive site management does not call for changing strategies on a whim. Instead, it calls for remedy optimization that reacts to new information. ASM would provide a systematic method to adapt to changing conditions, making decisions, and producing a remedy.”

ASM and use of risk assessment to guide remediation decisions—from the research, site operator, and regulator perspectives—will be part of a July 26 seminar and panel discussion through RemPlex, with speakers representing PNNL, Sealaska Technical Services, and the U.S. Environmental Protection Agency.