COAL COMBUSTION RESIDUAL
Coal Combustion Residual (CCR)
Coal combustion residual (CCR) is an umbrella term for the inorganic, solid byproducts that are left behind when coal is burned. Commonly referred to as coal ash, CCRs are one of the largest types of industrial waste produced in the U.S., according to the Environmental Protection Agency (EPA). The disposal of coal ash is regulated under the EPA’s CCR Rule.
What’s in Coal Ash?
Within the CCR umbrella, coal ash byproducts include:
· Fly ash: These are the fine, powdery particles that are captured by pollution control devices before they can “fly” up and out of a smoke stack.
· Bottom ash: Coarser than fly ash, these particles collect at the bottom of a coal furnace.
· Boiler slag: The molten coal ash that crystallizes and forms pellets when it comes into contact with water.
· Flue gas desulfurization gypsum (FGD gypsum): This synthetic gypsum is generated during the emission control systems process in coal-fired power plants. It is chemically identical to mined gypsum.
Depending on where the coal originated, coal ash may contain a number of substances known to be harmful to human health, including arsenic, mercury, lead, and chromium.
As utilities shift to natural gas and renewable resources, the amount of CCRs produced annually in the U.S. has dropped, from nearly 130 million tons of CCRs produced in 2014 to less than 70 million tons in 2020, according to the American Coal Ash Association (ACAA). However, the safe disposal of the CCRs that have been generated for decades remains an environmental challenge.
Why Is Coal Ash Regulated?
Early power plants allowed fly ash to be released into the atmosphere. With the advent of better pollution reduction technology and air pollution control regulations, utilities began capturing the ash and disposing of it in either dry landfills or wet surface impoundments, also known as coal ash ponds. Many of these disposal sites were unlined, with the potential to leak contaminates into groundwater.
Ash ponds also pose a threat to neighboring waterways. Because coal plants need a source for cooling water, they are typically built near lakes and rivers. This proximity poses serious environmental risks in cases of impoundment failures or severe flooding events. In response to an impoundment failure, the EPA developed the CCR Rule, which outlines the corrective actions that utilities must take to dispose of coal ash, along with technical standards, timelines, and requirements for inspections, monitoring, recordkeeping, and reporting.
Because of the EPA’s enforcement of the CCR Rule and the evolving energy mix favored by utility companies, virtually all unlined surface impoundments must close.
Americans have relied on coal as a source of electricity for more than a century, but the federal government only recently started regulating the disposal of the byproducts that result from burning coal. These byproducts are referred to as coal combustion residuals (CCR) or coal ash.
Electrical utilities have typically managed coal ash by disposing of it in either wet surface impoundments (coal ash ponds) or dry landfills. These disposal sites have kept CCRs largely out of the general public’s sight. However, recent impoundment failures vaulted coal ash into the headlines—and prompted the Environmental Protection Agency (EPA) to issue the CCR Rule, a new set of regulations for the safe disposal of coal ash.
What Is a Coal Ash Pond?
Coal ash can contain traces of a number of heavy metals that are dangerous to inhale and ingest. Cadmium can cause lung damage. Chromium is linked to asthma and lung cancer. Thallium can affect the nervous system, lungs, and other organs.
To prevent coal ash from entering the atmosphere, utility companies capture CCRs during the coal-burning process and dispose of them, often by mixing coal ash with water and storing this ash “slurry” in specially constructed ponds. While these ponds help to keep coal ash out of the air we breathe, they pose other environmental challenges.
Historically, many of these ponds were not lined, either with a geomembrane or a low-permeable clay liner. Leakage from unlined or poorly lined ash ponds can potentially contaminate groundwater and threaten the safety of drinking water sources. In addition, flood events or a structurally unstable pond can spill slurry into nearby waterways and the environment.
What Is the CCR Rule?
The CCR Rule establishes the minimum technical requirements for CCR disposal sites. The regulations address three risks of coal ash disposal:
• Contaminants leaking into groundwater
• Contaminants blowing into the air as dust
• Contaminants entering the environment because of an impoundment failure
The rule also outlines record keeping and reporting requirements, and requirements for making this information available to the public.
How Many Coal Ash Ponds Are There?
When the CCR Rule went into effect in 2015, the EPA estimated that utilities in the U.S. were disposing of CCRs at more than 735 active on-site coal ash ponds, averaging more than 50 acres in size (the equivalent of about 38 football fields) with an average depth of 20 feet, and at more than 310 active on-site landfills, averaging more than 120 acres in size (the equivalent of about 92 football fields) with an average depth of more than 40 feet.
The CCR Rule’s technical criteria and deadlines have been the subject of litigation and amendments ever since the rule was first issued. However, combined with energy industry trends moving away from coal, the CCR Rule has effectively spurred the closure of virtually all unlined coal ash ponds in the U.S.
How Are Coal Ash Ponds Closed under the CCR Rule?
In a January 2022 announcement of action to enforce the CCR Rule, the EPA emphasized that surface impoundments cannot be closed in a way that leaves coal ash in contact with groundwater because of the health and safety risks to nearby communities. Utilities have a few options when closing a coal ash pond under the CRR Rule: cap-in-place and closure-by-removal.
• Cap-in-place leaves the coal ash in place while taking steps to prevent it from contaminating the surrounding environment. The residuals are dewatered, excavated, compacted, and moved farther from waterways. Slopes are stabilized and additional structures may be constructed for further protection from flooding events. Finally, an engineered cover system of earthen and synthetic materials is placed over the residuals. In this scenario, ongoing monitoring of nearby aquifers is required by the CCR Rule to ensure that toxins do not leach into groundwater.
• Closure-by-removal transfers the coal ash away from flood zones and into a modern landfill with a protective liner. Once the CCRs are removed, the pond site is decontaminated, and continued groundwater monitoring is not required.
Another option utility companies have for complying with the rule is to recycle coal ash instead of disposing of it. The EPA defines “beneficial use” in the CCR Rule, and there are a number of markets that use coal ash. However, the production of coal ash in the U.S. exceeds demand in these markets, and coal ash that is not beneficially used must be disposed of in accordance with the CCR Rule.
What Is Ames Construction’s Experience in CCR Remediation?
For Ames Construction, there is no surface impoundment closure project that is too big or too complicated to take on. We understand the unique properties of coal ash slurry and have experience in all aspects of its handling, including dewatering, conditioning, and transporting. And with our heavy civil and industrial construction experience and one of the largest privately-owned equipment fleets in the country, we can build all of the infrastructure necessary to close a pond—including haul roads and bridges, concrete structures, retaining walls, and conveyor systems.
Our project delivery encompasses both the traditional bid-build approach and alternative delivery, in which we support the client and the client’s engineers through the pre-construction process, providing constructability, pricing, and schedule assessments. Because of our self-performing capabilities, we can make adjustments in labor and equipment through the life of a project to keep the work on schedule when unforeseen challenges arise.
From its founding in the 1960s, Ames has committed to the principle of “working in harmony with nature” to reflect the company’s determination to maintain the integrity of the environment. Our commitment to safeguarding natural resources is also a commitment to protecting the communities we serve. Check out our CCR remediation projects to learn more about our experience and capabilities.