CCR closure: How risk-based decision-making is reshaping outcomes

For the past decade, coal combustion residuals (CCR) regulations have followed a prescriptive approach: when contaminants exceed defined thresholds, cleanup is required—often regardless of whether anyone or anything is actually exposed.

The EPA is signaling interest in risk‑based, site‑specific closure and corrective action, allowing decisions grounded in actual exposure and risk.

That approach is intentionally conservative, but it can lead to expensive and disruptive remedies that don’t necessarily improve protection of human health or the environment.

Proposed revisions to the U.S. Environmental Protection Agency’s (EPA) CCR Rule suggest a different path. The EPA is signaling interest in risk‑based, site‑specific closure and corrective action, allowing decisions grounded in actual exposure and risk rather than one‑size‑fits‑all assumptions.

Using a case study from a coal-fired power plant, we’ll explore what that shift could look like in practice—and why it matters.

From prescriptive rules to practical, risk-based decisions

At its core, a risk‑based approach asks a simple but critical question: Are people or ecosystems actually exposed to concentrations that could cause harm?

Under the current CCR framework, the answer is assumed to be “yes” based solely on the presence of contaminants. This is what we call a “source” perspective on risk. Proposed changes would allow site‑specific evaluations that consider not just the source, but also a “receptor” perspective focused on how exposure to contamination might affect human health and the environment. Factors may include:

• Local hydrogeology and groundwater flow direction
• Whether and where human or ecological receptors are present
• Realistic exposure pathways
• Constituents of concern applicable to the receptors
• Existing and planned land use
• Engineered controls like caps and barriers

For many CCR sites—especially those in industrial settings with no human or ecological receptors—this shift could be a game-changer.

Case study: Why site context matters

Barr worked with a coal‑fired power plant undergoing repowering. The site sits on a narrow strip of land between a major river and a floodplain lake, with controlled access and no nearby drinking water wells. Surrounding areas are served by municipal water supply.

Over more than a decade, we completed extensive site investigations, compiling tens of thousands of data points from groundwater, surface water, soil, and sediment sampling. This information fed into a robust conceptual site model (CSM)—the backbone of any defensible risk‑based evaluation.

The CSM showed that:

• The site is located at a discharge boundary on a major river.
• Groundwater flows outward from the site toward the river and lake.
• Strong upward gradients prevent groundwater migration toward potential human receptors; there are no current or likely high-capacity pumping wells nearby.
• There are no current or likely future potable groundwater receptors.
• Worker exposure and surface water bodies are the only plausible human and ecological receptors.

That understanding set the stage for a focused, risk‑based evaluation.

Screening out what isn’t a risk

A common misconception is that risk‑based closure means “doing less.” In reality, it means doing the right work—and focusing on what matters.

Using the CSM, our team systematically evaluated potential exposure pathways under future site conditions. Several were ruled out because they would not exist under the proposed closure and redevelopment at the site:

• Groundwater ingestion: No drinking water wells now or in the future; this eliminated the groundwater-to-human-health pathway
• Direct soil contact: Engineered caps, pavement, and controlled access; this eliminated the worker and recreational exposure pathways

Other pathways were also considered and eliminated:

• Vapor intrusion: No volatile contaminants and no buildings over source areas
• Food‑chain exposure: No agricultural or subsistence use
• Terrestrial ecological exposure: Limited habitat due to industrial land use and low exposure potential for direct contact or plant uptake

Only one pathway remained: groundwater discharge to surface water, where aquatic organisms could potentially be exposed.

This is where the shift becomes clear. Under a prescriptive framework, groundwater exceedances might automatically trigger corrective action. Under a risk‑based framework, the absence of a receptor means there is an absence of the risk.

Shifting the focus to the receptor

Initial screening compared maximum groundwater concentrations to conservative surface water benchmarks. As expected, that process identified a smaller group of constituents to look at more closely.

But screening is not the same as risk.

In the refined evaluation, our team shifted from a source‑focused question (“Are groundwater concentrations high?”) to a receptor‑focused one: Are aquatic organisms actually exposed to harmful concentrations in surface water?

To answer that, we relied on:

• Extensive surface water sampling upstream and downstream of the site
• Comparisons to applicable ecological benchmarks
• A weight‑of‑evidence approach that considered chemistry, flow, and site conditions
• Explicit evaluation of uncertainty and conservatism

Rather than relying solely on modeled assumptions, we used real, site‑specific surface water data that reflects dilution, mixing, and attenuation processes.

The result: a high degree of confidence that the groundwater‑to‑surface‑water pathway did not pose an unacceptable risk to ecological receptors.

Closure without corrective action

Because no complete exposure pathways posed an unacceptable risk, the site could move forward with closure without active groundwater remediation.

Final actions focused on practical, protective measures, including:

• Removing post‑1975 CCR units
• Closure‑in‑place of legacy CCR beneath engineered caps
• Long‑term land use and institutional controls
• Ongoing monitoring to confirm performance

This approach not only protected human health and the environment—it also provided the owner with the liability assurance needed to redevelop and repower the site without fear of future disruption.

Why this shift matters for CCR closure

This case study shows what risk‑based CCR closure can look like under an evolving regulatory framework:

• Decisions grounded in real exposure, not assumptions
• Site‑specific science replacing uniform cleanup mandates
• Environmental protection achieved more efficiently and effectively

For sites with no groundwater receptors—or where pathways can be credibly eliminated—risk‑based approaches can avoid unnecessary excavation, reduce environmental impacts, and significantly lower costs, all while meeting the EPA’s goal of demonstrating no reasonable probability of adverse effects.

At the same time, risk‑based closure isn’t a shortcut. It requires strong data, a defensible CSM, technical expertise, and close coordination with regulators. The science has to hold up.

Comparative analysis

Barr has several ongoing projects in which we are either closing existing CCR units under the 2015 CCR Rule or conducting FER 2 investigations for CCRMU, legacy surface impoundments, or inactive surface impoundments that will require closure under the 2024 Legacy Amendments. The following cost breakdown compares some of the closure and corrective alternatives being considered, with assumed additions based on the April 2026 EPA-proposed revisions to the rule.

* Assumes difference is (cost of closure by removal + cost of corrective action) – (cost of risk-based closure in place + risk-based corrective action)

How Barr can help

Barr has been working with CCR sites for decades, helping clients navigate complex regulations, characterize challenging sites, and apply risk‑informed decision‑making with confidence. As the EPA’s proposed CCR rule changes continue to evolve, our team is well-positioned to help owners and operators understand what’s possible—and how to get there.

If you’re evaluating CCR closure options, planning redevelopment, or preparing for potential regulatory changes, Barr is here to help you navigate the path forward.

About the authors

Jim Aiken, vice president and senior hydrogeologist, has been focused on CCR and related issues since 1993, when he investigated a lithium plume from an active ash landfill in Michigan. His experience expanded during the late 90s and early 2000s, when utility clients became concerned about EPA plans to revisit the Bevill Amendment, which eventually led to the 2015 CCR rule. Most of that project experience involved field investigation, groundwater monitoring/statistics, and geochemical assessments at CCR landfills and impoundments. This work included characterizing CCR materials outside of known waste disposal areas.

Kevin Solie, senior environmental engineer, joined Barr in 2023 with more than three decades of experience with projects involving environmental permitting, regulatory interpretation, compliance, and reporting. Prior to joining Barr, Kevin served for 15 years as senior environmental compliance administrator at an electric power cooperative, where he was responsible for CCR Rule implementation and development of compliance strategies for its coal-fired fleet (including three CCR landfills and eight CCR surface impoundments).

Related project

Groundwater compliance assistance for CCR Rule

Barr has supported Heskett Station’s coal ash landfill since 2010, providing groundwater monitoring, geochemical analysis, and data evaluation services, and helping the client adapt to evolving CCR Rule requirements. By combining statistical analysis, environmental forensics, and rigorous data quality review, Barr helped the client avoid unnecessary corrective-action measures and significant remediation costs.