Product Code Database
An ash pond, also called a coal ash basin or surface impoundment,U.S. Environmental Protection Agency (EPA), Washington, D.C. "Hazardous and Solid Waste Management System; Identification and Listing of Special Wastes; Disposal of Coal Combustion Residuals from Electric Utilities." Proposed rule. Federal Register, , June 21, 2010. is an engineered structure used at coal-fired power stations for the disposal of two types of coal combustion products: bottom ash and fly ash. The pond is used as a landfill to prevent the release of ash into the atmosphere. Although the use of ash ponds in combination with air pollution controls (such as ) decreases the amount of airborne pollutants, the structures pose serious health risks for the surrounding environment.
Ash ponds use gravity to settle out large particulates (measured as total suspended solids) from power plant wastewater. This technology does not treat dissolved pollutants. The ponds generally have not been built as Landfill liner, and therefore chemicals in the ash can leach into groundwater and surface waters, accumulating in the biomass of the system.
Failure of a pond's earthen embankment can cause ash spills on adjacent land and rivers, with serious environmental damage, as evidenced in the 2008 Kingston Fossil Plant spill in Tennessee and the 2014 Dan River coal ash spill in North Carolina.
The flow of water through the fly ash and into ground water is controlled by using low-permeability clay layers and cutoff trenches/walls. Low-permeability clays have permeability on the order of 10−7 cm/s. Vertical flows through the foundation are controlled by siting fly ash ponds on areas of thick clay or rock layers that provide suitably low permeability through the base of the pond. Areas with high sub-surface permeability can be improved by importing suitable clay. Horizontal flows through the embankment are controlled using clay zones within the embankment. Cut off trenches and cut off walls are used to connect the embankment clay zones and the foundation clay layers. Cut off trenches are trenches that are dug into the selected low-permeability sub-surface layer and backfilled with clay to key the embankment clay zone into the sub-surface. Cut off trenches are generally used when the low permeability foundation layer(s) are near surface. Cut off walls are similar to cut off trenches, but are generally much deeper and narrower, and use either slurry or grout instead of clay.
In 2018 an environmental justice advisor to the US Environmental Protection Agency (EPA) stated that the increased toxic exposures from ash ponds will have disproportionate adverse health effects on low-income and minority communities.
A 2019 report by the Environmental Integrity Project stated that for U.S. coal-fired plants with available monitoring data, 91 percent of them have contaminated groundwater with "unsafe levels of toxic pollutants."
Historically, due to few federal and state regulations concerning ash ponds, most US power plants do not use , leachate collection systems, or other flow controls often found in municipal solid waste landfills. In 1980 the U.S. Congress defined coal ash as a "special waste" that would not be regulated under the stringent hazardous waste permitting requirements of the Resource Conservation and Recovery Act (RCRA). Congress also directed EPA to study the coal ash problem and decide whether further regulation would be appropriate. Pursuant to the Congressional directive, EPA reported in 2000 that coal fly ash did not need to be regulated as a hazardous waste.EPA (2000-05-22). "Notice of Regulatory Determination on Wastes From the Combustion of Fossil Fuels." Federal Register, .
Following a 2008 failure that caused the Tennessee Valley Authority's Kingston Fossil Plant coal fly ash slurry spill, EPA began developing regulations that would apply to all ash ponds in the US. EPA published a Coal Combustion Residuals (CCR) regulation in 2015. The agency continued to classify coal ash as non-hazardous (thereby avoiding strict permitting requirements under ), but with new restrictions:
Some of the provisions in the 2015 CCR regulation were challenged in litigation, and the United States Court of Appeals for the District of Columbia Circuit remanded certain portions of the regulation to EPA for further rulemaking.
EPA also published an effluent guidelines (wastewater) regulation in 2015 pursuant to the Clean Water Act.EPA. "Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category." . 2015-11-03. The regulation limits discharges of toxic metals from power plants, including ash ponds and other wastestreams. The Agency estimated that the regulation would reduce the industry's metals discharges of 1.4 billion pounds annually. In 2020 EPA published a final rule that reversed some provisions of the 2015 wastewater regulation. The revised regulation extended the compliance deadline for some power plants, and exempted some others completely from the more stringent 2015 requirements.EPA (2020-10-13). "Steam Electric Reconsideration Rule." Final rule. Federal Register, In May 2024 EPA published a final rule that reverses some aspects of the 2020 rule and tightens the wastewater limitations for some facilities.EPA (2024-05-09). "Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category." Final rule.
Following a court remand, EPA published its "CCR Part A" final rule on August 28, 2020 requiring all unlined ash ponds to retrofit with liners or close by April 11, 2021. Some facilities may apply to obtain additional time—up to 2028—to find alternatives for managing ash wastes before closing their surface impoundments.EPA. "Hazardous and Solid Waste Management System: Disposal of Coal Combustion Residuals From Electric Utilities; A Holistic Approach to Closure Part A: Deadline To Initiate Closure." . 2020-08-28. EPA published its "CCR Part B" rule on November 12, 2020, which allows certain facilities to use an alternative liner, based on a demonstration that human health and the environment will not be affected.EPA (2020-11-12). "Hazardous and Solid Waste Management System: Disposal of CCR; A Holistic Approach to Closure Part B: Alternate Demonstration for Unlined Surface Impoundments." Final rule.
On January 11, 2022 EPA announced an enforcement action involving ash ponds at certain coal-fired plants in Indiana, Ohio, Iowa and New York. The agency's proposal would deny the plants' requests for extensions beyond the 2021 deadline and would require them to close their ash ponds ahead of their proposed schedules. EPA sent warning letters to four additional plants. EPA received a total of 57 extension requests. In November 2022 the agency announced its initial final determination on an extension request, denying a request submitted by a plant in Ohio. As of 2024 EPA has published proposed determinations for additional plants and the review process is ongoing. Each proposed determination is subject to a public comment period.
In response to litigation, EPA published a final RCRA rule in May 2024 setting regulatory requirements for active and inactive CCR facilities, including groundwater monitoring, corrective action, closure, and post-closure care requirements.EPA (2024-05-08). "Hazardous and Solid Waste Management System: Disposal of Coal Combustion Residuals From Electric Utilities; Legacy CCR Surface Impoundments." Final rule.
There are some initiatives, such as a 2015 initiative by Duke Energy, to excavate existing ash ponds to reduce the environmental effects of coal-burning power facilities on the surrounding environment.
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