Developing Tools for Coal Ash Remediation

Known as coal combustion residuals (CCR) or coal combustion products (CCP), inorganic constituents at coal ash disposal sites and decommissioned coal power plants are potential hazards to human health and the environment, as well as potential liabilities for utility companies. Intersecting groundwater can leach constituents from coal ash landfills and impoundments and, depending on the hydrogeologic properties of the surrounding environment, transport plumes of dissolved constituents of concern, such as arsenic and metals, potentially impacting drinking water sources. 

THE CHALLENGE

Given new and emerging regulations, including the Environmental Protection Agency's Final Rule for Legacy CCR Surface Impoundments and CCR Management Units, utility companies are prioritizing environmental risk assessments and performance evaluations for CCP mitigation methodologies. 

Our client turned to Exponent to assess the performance of two CCP mitigation methods: closure-in-place (CIP), which involves sealing coal ash waste on site with an impermeable membrane combined with other engineering controls, and closure-by-removal (CBR), which involves removing the waste from the site to a landfill. Exponent's work is intended to support site-specific selection of effective corrective actions over a range of hydrogeological and geochemical variations that are anticipated to occur at CCP sites.

EXPONENT'S MULTIDISCIPLINARY SOLUTION

Exponent's multidisciplinary team of ecologists, biologists, and environmental and data scientists created and leveraged bespoke modeling tools to simulate the long-term performance of remediation technologies for CCP deposits with intersecting groundwater.

OUR Impact

Exponent's analysis demonstrated that corrective action at CIP sites with intersecting groundwater could be as effective as CBR in addressing releases to groundwater, with relative performance influenced by site and constituent factors, as well as the choice of remediation technologies. While results are not specific to any given site, the simulations equipped our client with the tool they needed to evaluate CCP remediation options for a wide range of hydrogeological and geochemical conditions and for a range of constituents.

The modeling and data analysis approaches developed by Exponent have the potential to benefit power plant operators, conventional landfill or mining operations, and other organizations undertaking due diligence efforts. Whether buying or selling land or physical assets, clients can leverage Exponent's geochemical modeling expertise to understand risk related to the potential migration of inorganic constituents in a saturated subsurface environment.

As utilities pursue net-zero emissions goals and evaluate the potential to convert decommissioned U.S. coal power plant sites to alternative uses, site-specific feasibility and chemical fate and transport studies will be critical to determining whether a site would be appropriate for nuclear power or renewables generation.