Coal combustion residuals — coal ash — are the second-largest industrial waste stream in America, behind only mining waste. Every year, the nation's coal-fired power plants produce over 100 million tons of the stuff: fly ash captured from flue gases, bottom ash collected from furnace floors, boiler slag, and flue gas desulfurization materials from scrubbers. It's the unavoidable byproduct of burning coal for electricity, and after decades of largely ignoring it, America is slowly reckoning with what to do about the mountain.
What's in Coal Ash
Coal ash is not inert dirt. It concentrates the heavy metals and trace elements present in the original coal — arsenic, mercury, lead, selenium, cadmium, chromium, boron, lithium, and thallium, among others. When coal burns, these elements don't disappear. They concentrate in the ash at levels significantly higher than in the original coal.
A 2007 EPA risk assessment found that living near an unlined coal ash disposal site increases cancer risk by up to 1 in 50 — a rate the agency called "outrageously high" compared to the 1-in-10,000 threshold that typically triggers regulatory action. Groundwater monitoring data from hundreds of coal ash sites shows arsenic, selenium, and other contaminants exceeding drinking water standards, often by orders of magnitude.
The Disposal Disaster
For decades, coal ash disposal was essentially unregulated. Utilities dumped ash into unlined surface impoundments — fancy language for open ponds — or dry landfills with minimal engineering. There are an estimated 1,100+ coal ash disposal sites across the United States, and hundreds lack basic environmental controls like liners, leachate collection, or groundwater monitoring.
The wake-up call came on December 22, 2008, when a dike at the Tennessee Valley Authority's Kingston Fossil Plant failed, releasing 5.4 million cubic yards of coal ash slurry across 300 acres of land and into the Emory River. It was the largest industrial spill in American history. Homes were destroyed. The river was contaminated. And over 900 workers involved in the cleanup — many of whom were told the ash was safe — have since reported severe illnesses. More than 50 have died.
Kingston forced the EPA's hand. In 2015, the agency finalized the Coal Combustion Residuals (CCR) rule under Subtitle D of RCRA — regulating coal ash as a non-hazardous solid waste. The rule required groundwater monitoring, established structural integrity criteria for impoundments, and set closure requirements for sites that couldn't meet the standards. But by classifying coal ash as non-hazardous — despite its demonstrated toxicity — the rule left enforcement largely to the states and the industry itself through a "self-implementing" compliance framework.
The result has been uneven at best. As of 2025, hundreds of unlined impoundments remain open or are in various stages of closure. Many utilities have chosen "closure in place" — capping the ash where it sits rather than excavating it — which leaves the contamination source permanently in contact with groundwater. Environmentalists and affected communities argue this is simply entombing the problem.
The Recycling Story
Here's where it gets complicated — and more interesting.
About 55-60% of coal ash produced annually is beneficially reused rather than disposed. The primary applications are well-established and, in many cases, genuinely beneficial:
Concrete. Fly ash is a proven supplementary cementitious material (SCM). When substituted for 15-30% of Portland cement in concrete, fly ash improves workability, reduces heat of hydration, increases long-term strength, and dramatically improves resistance to sulfate attack and alkali-silica reaction. The carbon footprint reduction is significant — every ton of fly ash replacing a ton of Portland cement avoids roughly 0.9 tons of CO₂ emissions from cement manufacturing. The concrete industry uses approximately 13-15 million tons of fly ash annually.
Structural fills and embankments. Coal ash — particularly bottom ash and stabilized fly ash — is used as engineered fill for highway embankments, parking areas, and structural backfill. When properly placed and compacted, it performs comparably to natural aggregates at lower cost.
Wallboard. Flue gas desulfurization (FGD) gypsum — the calcium sulfate produced by scrubbers — is chemically identical to mined gypsum and is used extensively in wallboard manufacturing. Over 50% of American wallboard now contains synthetic gypsum from coal plant scrubbers.
Road base and soil stabilization. Fly ash mixed with lime or cement creates a durable road base material. Its pozzolanic properties — the ability to react with calcium hydroxide to form cementitious compounds — make it effective for stabilizing weak soils.
When "Recycling" Isn't
Not all beneficial reuse is created equal. The line between legitimate recycling and disguised disposal has been a contentious issue since the EPA first considered coal ash regulation in the 1990s.
The concern centers on unencapsulated uses — applications where coal ash is placed in direct contact with soil and water without the binding matrix that concrete provides. Structural fills, mine reclamation, road sub-base, and agricultural applications all involve spreading coal ash across the landscape in ways that can allow leaching of heavy metals into groundwater and surface water.
A 2010 EPA investigation identified 157 damage cases linked to coal ash disposal and beneficial reuse — sites where coal ash had contaminated groundwater, surface water, or drinking water supplies. Some of these were disposal sites. Others were "beneficial reuse" sites where ash was used as fill or placed in unlined settings.
The distinction matters because coal ash classified as "beneficially reused" is exempt from even the limited regulations that apply to disposal. If a utility sends ash to an unlined fill site and calls it beneficial reuse, that ash faces fewer regulatory requirements than if the same ash went to a permitted landfill. The incentive structure can perversely encourage less protective management.
Several states have tightened their beneficial reuse regulations. Indiana, for example, restricted unencapsulated fill applications after coal ash was linked to groundwater contamination at multiple sites. Pennsylvania requires permits for most coal ash beneficial use applications. But the regulatory landscape remains a patchwork.
The Opportunity Nobody's Seizing
The irony of coal ash is that it contains economically valuable materials that we're either burying or using in low-value applications while mining virgin materials to meet demand.
Coal ash contains recoverable quantities of rare earth elements — the critical minerals essential for electronics, renewable energy systems, and defense applications. Research by the Department of Energy's National Energy Technology Laboratory has demonstrated that coal ash can contain 200-800 ppm of rare earth elements, with some sources exceeding 1,000 ppm. While lower than conventional rare earth ore grades, the concentration is high enough to be economically viable with advanced extraction techniques — particularly given that the "mining" has already been done and the material is sitting in ponds and landfills.
Aluminum recovery from coal ash is technically feasible and has been demonstrated at pilot scale. Cenospheres — hollow fly ash microspheres — command premium prices ($1,000-4,000 per ton) for use in lightweight composites, drilling fluids, and specialty coatings. They're literally floating on the surface of ash ponds at power plants across America.
The barrier isn't technology — it's economics and regulation. Extracting value from coal ash requires investment in processing infrastructure, and the regulatory uncertainty around coal ash classification makes investors cautious. Is it a waste? A resource? The answer determines everything from permitting to liability.
Where EPR Foundation Stands
Coal ash is real waste from real energy production that powered American industry for over a century. Pretending it's not there isn't an option — there are over a billion tons of it in legacy disposal sites across 45 states.
We support three principles. First, encapsulated reuse — coal ash in concrete, wallboard, and bound applications — is genuinely beneficial and should be encouraged. It sequesters contaminants in a stable matrix, displaces virgin materials, and reduces carbon emissions. Second, unencapsulated placement of coal ash should be regulated with the same groundwater protections as disposal, because the environmental risk profile is functionally identical. Third, the federal government should invest in coal ash-to-critical-minerals research and pilot programs. We're importing rare earth elements from China while sitting on a domestic supply that's already been mined, concentrated, and stockpiled. That's not just an environmental issue — it's a strategic one.
The 100-million-ton-per-year coal ash problem isn't going away, even as coal plants close. The legacy ash will outlast the plants that created it by centuries. How we manage it — as a liability or an opportunity — is a choice we're making right now.