Coal-fired power plants face an increasing challenge of complying with a wide, ever-changing range of environmental regulations. In the last decade, constituents found in coal combustion residuals (CCR) have come under heavy scrutiny. One of those constituents, boron, has recently started receiving more attention from the U.S. Environmental Protection Agency (EPA).
A conservative constituent, boron is not reactive and is currently categorized as an Appendix III, detection monitoring constituent. High levels of boron can be found in CCR and can also occur naturally. Exposure at certain levels can cause negative health affects in humans and animals. Currently, utility owners and operators do not necessarily undertake remediation efforts based solely on high boron levels, because such actions are not required by EPA regulations.
However, in response to legal challenges, a change in the classification of this constituent is being evaluated by the EPA, with boron expected to be added to the list of assessment monitoring constituents in Appendix IV. The EPA first proposed adding boron to Appendix IV on March 15, 2018. This change would require that coal plants undertake the evaluation of corrective measures then implement corrective action to remediate certain levels of boron in groundwater resulting from releases from CCR units.
More recently, on Aug. 14, 2019, the EPA proposed establishing an alternate risk-based groundwater protection standard (GWPS) for boron, as the agency had done previously for other Appendix IV constituents without established maximum contaminant levels. While it's currently unknown when the EPA will finalize proposed changes to the way boron is treated under the federal CCR regulations, it’s important that utility owners and operators prepare now for a change that may impact their operations in the near future.
Treatment Challenges
Boron, while present in CCR, is also a naturally occurring element. This can make it difficult to differentiate between what concentrations result from background levels and what concentrations are directly attributed to a release from CCR units. Plant owners and operators perform detection monitoring to determine levels of constituents in the EPA’s Appendix III Constituents list. If data collected on these constituents exceeds background levels, the plant is required to perform assessment monitoring, during which owners and operators test for constituents listed in Appendix IV and then compare that data against the appropriate groundwater protection standard.
Should the EPA’s proposed regulation change the acceptable level of boron in CCR, it could require plants to move from assessment monitoring to corrective measures in order to mitigate the risk and remove contaminants from affected groundwater. This would create additional challenges for owners and operators, as there are currently no proven in situ treatment measures to permanently immobilize boron in the subsurface, requiring extensive and costly groundwater extraction and ex situ treatment processes.
Treatment methods that have been shown to be effective for removing boron include distillation, ion exchange and reverse osmosis. Of these, ion exchange is likely to be the more efficient and cost-effective. There has also been research evaluating sorbents capable of removing boron from wastewater using metal oxides and even plant-based materials.
If the proposed GWPS for boron becomes final, it may be sufficiently higher than groundwater concentrations found at many facilities, giving plant owners and operators the ability to avoid planning remediation efforts solely based on boron concentrations in groundwater. Challenges could still arise if concentrations of other Appendix IV constituents lead to extraction and treatment of groundwater that also contains high levels of boron and is subject to discharge limits lower than allowable groundwater concentrations. These potential issues should be considered when planning near- and long-term plant wastewater projects throughout the time of operation, closure and post-closure care for CCR units.
Future Preparation
While it’s unclear when, exactly, the EPA’s new rule regarding boron might be put into place, coal-fired plant owners and operators should start preparing for operational impacts today. Reviewing previously collected data on CCR constituents would help these organizations understand current boron levels in groundwater and whether there would be a need to develop and evaluate potential remediation strategies.
Coal-fired power plants affected by changes in CCR management rules and effluent limitation guidelines are required to make changes to bottom ash management systems.