Power companies are faced with a tremendous new challenge at coal combustion residual (CCR) sites due to the EPA’s recently published Legacy CCR Rule, which requires an introduction of CCR provisions for inactive electric utility surface impoundments and the inclusion of many additional CCR management units. The clock starts for compliance on November 8, 2024, the anticipated effective date of the rule, after which compliant monitoring well network installations will be required within three to four years. As a result, a clearly defined and communicated understanding of the site’s natural hydrogeologic controls on groundwater flow — the conceptual site model (CSM) — is imperative for groundwater monitoring program design. 

A cost-effective and compliant monitoring program achieves comprehensive monitoring with the right number of well screens installed in optimal locations, defined in three dimensions. While the uncertainties associated with this challenge may seem daunting, the application of advanced geoscience techniques to existing site data provides an opportunity to leverage past investigations and add value to CCR programs.  

Decades of groundwater investigation and remediation have conclusively shown that aquifers are extremely heterogenous and that groundwater flow is typically dominated by one or more preferential pathways within the overall aquifer volume. Outside of the preferential pathways, less-permeable strata are prone to retain contaminants and act as persistent sources. This complexity has, in many cases, severely limited the effectiveness of groundwater cleanups and prolonged their time frames.

However, these challenges can be addressed using environmental sequence stratigraphy (ESS) techniques for data analysis. ESS, which is acknowledged by the EPA as a best practice for developing CSMs, has been employed at more than 100 Department of Defense installations across the country, improving groundwater remediation project performance and optimizing the design of well networks. 

ESS can be applied to existing well and boring data with no additional field activities to help identify and strategically target meaningful site data gaps and serve as a robust method to implement a third-party review of complex sites. Notably, as facilities increase the number of CCR units that require independent monitoring networks, as a result of the new Legacy CCR Rule, a clearer understanding of groundwater movement and quality throughout the site will become increasingly valuable. Return on investment in ESS analyses is realized by streamlining the process of getting into compliance, reliably staying in compliance, and reducing long-term risk and uncertainty. 

Applying ESS effectively requires a deep understanding of how the sediments that make up the aquifer (or aquitard) were deposited, the types of sediment or rocks found underground — which borehole data show — and the geological age and setting in which the site's water-bearing layers were originally deposited. Once these elements are understood, project teams can map out the dimensions and geometry of the site's hydrostratigraphy to define the plumbing of your site, identify the site's underground plumbing system for groundwater flow and the preferred pathways that the water takes, and set up the appropriate monitoring systems.

Additionally, the newfound knowledge can help produce a more comprehensive picture of the site. This is particularly true when knowledge of the complex system of groundwater flow — uncovered by ESS — is combined with information about chemical and biological components that work together to influence how contaminants move and break down in groundwater. Such a realistic understanding of groundwater flow and contaminant movement helps identify remaining data gaps and fills them systematically. This reduces uncertainty, meets monitoring requirements and allows for accurate assessment of necessary corrective measures with high confidence.

The key to unlocking a future-focused approach for CCR sites is to thoroughly understand the site's geology, hydrogeology and related processes. This knowledge allows project teams to effectively map out groundwater flow and contaminant movement and develop the appropriate monitoring and remediation plans.

The subsurface is a critical factor creating unpredictability in CCR site management. It poses risks to achieving and maintaining compliance, potentially compromising long-term cost certainty. By adopting ESS, the uncertainty of the subsurface is challenged head-on, aligning project teams and regulators around the shared complexity of the site. ESS introduces a proven EPA best-practice approach to site data to clearly define the CSM, providing a proactive course of action in addressing implications of the Legacy CCR Rule. A meaningful understanding of the subsurface promotes collaboration and trust among stakeholders, encourages open dialogue and steadily advances projects toward long-term compliance and cost stability.


Navigating the complexities of subsurface uncertainties is key to compliance and efficient site management. Discover how adopting an integrated and proactive approach with ESS guidance can transform your project outcomes. 


Mark Rokoff is a business development director and CCR specialist at Burns & McDonnell. With more than two decades of experience, Mark has worked with some of the nation’s largest power utilities to deliver safe, cost-effective solutions to complex environmental challenges. His experience includes regulatory compliance, innovative site and design solutions, and water management, particularly within the evolving coal combustion products sector.