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White Papers

Biotic and Abiotic Reduction to Achieve Groundwater Compliance at CCR Sites

Graham Crockford, VP & Steve Markesic | November 17, 2022

Because of challenges related to the Federal Coal Combustion Residuals (CCR) Rule, owners and operators of CCR units are actively making decisions on corrective measures to address CCR effects on water quality, often implementing closure options and remedy selection to achieve compliance. Because the Rule requires that an owner/operator meet groundwater protection standards (GWPS) under a stringent timeframe, many are seeking ways to use in-situ technologies to expedite GWPS compliance through enhanced attenuation (EA) strategies.

Download and Read our White Paper for More Details About:

  • Reductants and Biotic Processes
  • Biochemical Reduction Testing
  • Arsenic and Selenium Stabilization
  • ZVI Testing
  • Biowall Testing

Download the White Paper

TRC conducted two case studies to test different EA strategies. In both studies, chemical and biological reduction to stabilize metals at former CCR sites were evaluated.

The first case study tested the application of Zero Valent Iron (ZVI) via direct-push injection techniques as an alternative means of attenuating a plume with persistent levels of arsenic. Based on the results from these tests, a pilot-scale test using a mixture of ZVI and ferrous sulfate was proposed and is currently being implemented.

The second case study had a groundwater extraction system installed at a former CCR impoundment to provide enhanced natural attenuation. This case found that a permeable reactive barrier (PRB) was not recommended due to the concern of long-term permeability issues, which could result in the diversion of groundwater flow around the PRB.

These case studies provide valuable insight into implementing groundwater compliance strategies. Based on the data, it’s important to obtain a clear site conceptual model, incorporating geochemistry, hydrogeology, and attenuation parameters, and ensure the system is stable before assessing or making recommendations.

We have found that the removal of CCR from an impoundment does not always result in a quick attainment of GWPS, and Monitored Natural Attenuation (MNA) may take time. Reductant treatment technologies such as ZVI can be effective at stabilizing metals through sorption and coprecipitation reactions. The addition of ZVI not only facilitates these abiotic reactions, but also promotes biotic reactions that occur simultaneously. Once it is determined that EA may be appropriate for the site, a feasible application method needs to be evaluated. As part of the EA approach, it is also important to incorporate a monitoring program to ensure that the appropriate geochemical conditions are sustained, and that remobilization of metals will not occur.

Graham Crockford, VP

Graham has over 32 years of experience in the fields of consulting, environmental engineering, geology, and hydrogeology. He currently serves as a Unit Leader for TRC’s Environmental, Construction, and Remediation business, where he drives TRC’s strategic direction to serve our client and business goals. With decades of experience working with legacy coal-fired power generation, his focus is also directed to support our clients achieve their renewable energy and decarbonization goals.  In this role, he fosters the connection of various TRC disciplines, and also engages in quality assurance, quality control and client experience.  He also serves as a Client Services Manager/Project Manager for TRC’s utility and industrial clients. Graham has a long history with the liquid/solid waste/CCR industry, including active-life and post-closure care. He has extensive experience in landfill permitting, wetland mitigation, and construction/operations. He also served as a program manager for a regional waste management firm for 4 years where he was responsible for implementing groundwater protection and compliance programs for over 12 TSDFs across the US. In the early 1990s Graham served on Michigan Waste Industry Association’s technical standards subcommittee providing advocacy and industry perspective during development of Michigan’s Part 115 Solid Waste statute/rules in response to Subtitle D. Contact him at

Steve Markesic

Steve has over 21 years of experience in the environmental industry specializing in the design and implementation of various in-situ remediation approaches at active and inactive facilities.  His qualifications include extensive hands-on implementation, design, cost estimating, bid preparation, and project management.  He has worked on projects throughout the United States and internationally.  He has experience in applying remedial techniques in varying geologic conditions including low permeability, high groundwater flow, and fractured bedrock.  He has extensive experience using remediation amendments to promote aerobic, anaerobic, and co-metabolic bioremediation, stabilization, and in-situ chemical oxidation, with some experience in steaming and NAPL product recovery.  Steve’s experience with contaminants ranges from chlorinated alkenes, alkanes, petroleum hydrocarbons, and heavy metals. He currently serves in the capacity of Senior Hydrogeologist/Associate Project Manager in the Environmental, Construction, and Remediation division and is based out of the Ann Arbor, Michigan office. Contact him at

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