Ash pond

An ash pond, also called a coal ash basin or surface impoundment,[1], is an engineered structure used at fossil fuel 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 wet scrubbers) decreases the amount of airborne pollutants, the structures pose serious health risks for the surrounding environment.[2]

A coal-fired power plant with surface impoundments

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.[3] The ponds generally have not been built as lined landfills, and therefore chemicals in the ash can leach into groundwater and surface waters, accumulating in the biomass of the system.[4][5][6]

In the United States, federal design standards for ash ponds were strengthened in 2015, although various provisions of the new regulations are on hold as of 2020, pending ongoing litigation.

Pond design

Ash ponds are generally formed using a ring embankment to enclose the disposal site. The embankments are designed using similar design parameters as embankment dams, including zoned construction with clay cores. The design process is primarily focused on handling seepage and ensuring slope stability.

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[7] and the 2014 Dan River coal ash spill in North Carolina.[8]

Disposal methods

The wet disposal of ash into ash ponds is the most common ash disposal method,[9] but other methods include dry disposal in landfills. Dry-handled ash is often recycled into useful building materials. Wet disposal has been preferred due to economic reasons, but increasing environmental concerns regarding leachate from ponds has decreased the popularity of wet disposal.[9] The wet method consists of constructing a large "pond" and filling it with fly ash slurry, allowing the water to drain and evaporate from the fly ash over time.[10]

Leachate from fly ash can contain heavy metals in excess of allowable U.S. standards under the Resource Conservation and Recovery Act (RCRA).[11] 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.

Health and environmental impacts

Not all substances present in coal will burn, and hence the non-combustible material is present in more concentrated amounts in coal ash than in coal itself. Substances commonly found in coal ash include arsenic, barium, beryllium, boron, cadmium, nickel, lead, mercury, molybdenum, selenium and thallium. Elevated levels of radioactivity may also be present.[12] Many of these substances, especially heavy metals, can have negative effects on humans when ingested. Because of biomagnification, the concentration of unwanted chemicals in animals can increase up a food chain (similarly to mercury in tuna). Coal ash, a product of combustion, concentrates these elements and can contaminate groundwater or surface waters if there are leaks from an ash pond.[13]

In the United States, coal ash is a major component of the nation's industrial waste stream.[14] As of 2012 approximately 60 percent of US coal ash was disposed in surface impoundments and landfills. The US had 310 active on-site landfills in 2012, averaging more than 120 acres in size with an average depth of over 40 feet, and more than 735 active on-site surface impoundments, averaging more than 50 acres in size with an average depth of 20 feet.[15] In 2017, 38.2 million short tons (34.7×10^6 t) of fly ash, and 9.7 million short tons (8.8×10^6 t) of bottom ash were generated.[16]

A 2019 report by the Environmental Integrity Project states that for U.S. coal-fired plants with available monitoring data, 91 percent of them have contaminated groundwater with "unsafe levels of toxic pollutants."[17]

An environmental justice advisor to the US Environmental Protection Agency (EPA) has stated that the increased toxic exposures from ash ponds will have disproportionate adverse health effects on low-income and minority communities.[18]

Regulation in different countries

United States

In the United States, due to few federal and state regulations concerning ash ponds, most power plants do not use geomembranes, leachate collection systems, or other flow controls often found in municipal solid waste landfills.[10] 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 RCRA.[19] In 2000, EPA stated that coal fly ash did not need to be regulated as a hazardous waste.[20][21]

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 RCRA Subtitle C), but with new restrictions:

  1. Existing ash ponds that are contaminating groundwater must stop receiving CCR, and close or retrofit with a liner.
  2. Existing ash ponds and landfills must comply with structural and location restrictions, where applicable, or close.
  3. A pond no longer receiving CCR is still subject to all regulations unless it is dewatered and covered by 2018.
  4. New ponds and landfills must include a geomembrane liner over a layer of compacted soil.[22]

In 2016, the United States Court of Appeals for the District of Columbia Circuit vacated the "early closure" provisions in the regulation at 40 CFR 257.100. EPA then extended the compliance date for inactive ponds that attempted to utilize the early closure provisions.[23] In 2018, at the request of industry, EPA extended the compliance date for unlined ash ponds from 2019 to 2020, and provided more flexibility to state agencies in determining compliance with standards.[24][25] The 2018 regulation was challenged in litigation and remanded by the court to EPA for further revision. The court ruled that EPA failed to adequately address the problems with unlined ponds, many of which continue to leak into groundwater.[26] In 2019, the court agreed to a voluntary remand while allowing the 2020 compliance deadline for unlined ponds to stay in effect, pending further rulemaking.[27]

EPA published a proposed rule on August 14, 2019 that would use location-based criteria, rather than a numerical threshold (i.e. impoundment or landfill size) that would require an operator to demonstrate minimal environmental impact so that a site could remain in operation.[28] On December 2, 2019 EPA published another proposed rule that would establish an August 31, 2020 deadline for facilities to stop placing ash in unlined impoundments. The proposal would also provide additional time for some facilities—up to eight years—to find alternatives for managing ash wastes before closing surface impoundments.[29][30] A final rule is pending as of early 2020.[31]

Netherlands

Ash ponds are not allowed in the Netherlands, as they are a type of landfill. Instead, all coal ash is recycled in the Netherlands.[32]

Remediation

Remediation options include "capping, dewatering and/or stabilizing, consolidating into a new landfill, disposing off site, converting to wetlands, or any combination of these options."[33]

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.[34][35]

See also

References
  1. 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, 75 FR 35130, June 21, 2010.
  2. Erickson, Camille (October 7, 2019). "Mixing water, Powder River Basin coal ash dangerous to human health, new research finds". Casper Star-Tribune. Casper, WY.
  3. "Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category". EPA. 2018-11-30.
  4. Brooke, Nelson (June 5, 2019). "New Interactive Maps of Groundwater Pollution Reveal Threats Posed by Alabama Power Coal Ash Pits". Black Warrior Riverkeeper. Birmingham, AL.
  5. Springer, Patrick (March 13, 2019). "Report: Unsafe coal ash contamination found in North Dakota groundwater". Bismarck Tribune. Bismarck, ND.
  6. Tosheff, Taylor (2019-07-31). "York: Brunner Island power plant owners agree to $1M penalty, coal ash cleanup". Harrisburg, PA: ABC27 News.
  7. Dewan, Sheila (2008-12-23). "Water Supplies Tested After Tennessee Spill". The New York Times.
  8. "Case Summary: Duke Energy Agrees to $3 Million Cleanup for Coal Ash Release in the Dan River". Enforcement. EPA. 2017-03-15.
  9. McLaren, R. J. & A. M. DiGioia (1987). "The Typical Engineering Properties of Fly Ash". In Woods, R. D. (ed.). Geotechnical Practice for Waste Disposal. Reston, VA: American Society of Civil Engineers.
  10. Kessler, K. A. (1981). "Wet Disposal of Fossil Plant Waste Case History". Journal of the Energy Division. American Society of Civil Engineers. 107 (2).
  11. Theis, T. L. & Marley, J.J. (1979). "Environmental Consideration for Fly Ash". Journal of the Energy Division. American Society of Civil Engineers. 105 (1).
  12. Walton, Robert (March 5, 2018). "Utilities find groundwater contamination, radioactivity at unlined coal ash sites". Utility Dive. Washington, D.C.: Industry Dive, Inc.
  13. Schlossberg, Tatiana (2017-04-15). "2 Tennessee Cases Bring Coal's Hidden Hazard to Light". The New York Times.
  14. "Coal Ash Basics". EPA. 2019-02-05.
  15. "Frequent Questions about the 2015 Coal Ash Disposal Rule". EPA. 2014-12-16.
  16. 2017 Coal Combustion Product Production & Use Survey Report (PDF) (Report). Farmington Hills, MI: American Coal Ash Association. 2018.
  17. "Coal's Poisonous Legacy". Washington, D.C.: Environmental Integrity Project. 2019-03-04.
  18. McKenna, Phil (2018-03-15). "EPA Environmental Justice Adviser Slams Pruitt's Plan to Weaken Coal Ash Rules". New York: InsideClimate News.
  19. "Special Wastes". Hazardous Waste. EPA. 2018-11-29.
  20. EPA (2000-05-22). "Notice of Regulatory Determination on Wastes From the Combustion of Fossil Fuels." Federal Register, 65 FR 32214.
  21. Luther, Linda (2013-08-06). Background on and Implementation of the Bevill and Bentsen Exclusions in the Resource Conservation and Recovery Act: EPA Authorities to Regulate "Special Wastes" (Report). Washington, D.C.: U.S. Congressional Research Service. R43149.
  22. EPA. "Hazardous and Solid Waste Management System; Disposal of Coal Combustion Residuals From Electric Utilities." 80 FR 21301, 2015-04-17.
  23. EPA. "Extension of Compliance Deadlines for Certain Inactive Surface Impoundments; Response to Partial Vacatur." 81 FR 51802, 2016-08-05.
  24. EPA. "Amendments to the National Minimum Criteria (Phase One, Part One)." 83 FR 36435, 2018-07-30.
  25. Eilperin, Juliet; Dennis, Brady (2018-07-17). "EPA eases rules on how coal ash waste is stored across U.S." The Washington Post.
  26. "DC Circuit Rules EPA Dropped Ball on Coal Ash Storage Rules". Courthouse News Service. 2018-08-22.
  27. Green, Douglas H.; Houlihan, Michael (2019-04-24). "D.C. Circuit Court Remands CCR Deadline Extension to EPA". Environment, Energy, and Resources Section. Washington, DC: American Bar Association.
  28. EPA. "Hazardous and Solid Waste Management System: Disposal of Coal Combustion Residuals from Electric Utilities; Enhancing Public Access to Information; Reconsideration of Beneficial Use Criteria and Piles; Proposed Rule." Federal Register, 84 FR 40353. 2019-08-14.
  29. 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." Proposed rule. Federal Register, 84 FR 65941. 2019-12-02.
  30. Smith-Schoenwalder, Cecelia (2019-11-04). "EPA Moves to Rollback Coal Power Plant Waste Rules". U.S. News.
  31. "Disposal of Coal Combustion Residuals from Electric Utilities Rulemakings". EPA. 2020-01-10.
  32. "Best practices for managing power plant coal ash". www.powerengineeringint.com. Retrieved 2019-06-17.
  33. Johnson, Mark; Nillson, Kent (2014-12-01). "Construction Considerations Are Key in Closure Planning for Coal Ash Ponds". Power Magazine. Rockville, MD: Access Intelligence, LLC.
  34. "Coal Ash". Charlotte, NC: Catawba Riverkeeper Foundation.
  35. "Ash Management & Safe Basin Closure". Charlotte, NC: Duke Energy.
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