BOULDER — When Xcel Energy stopped burning coal at its Valmont Power Station in 2017, it left 1.6 million tons of toxic coal ash on the property, and now that waste is leaking hazardous metals into groundwater, threatening nearby drinking-water wells.
Xcel plans to scoop most of the coal ash from a landfill at the site and turn it into an ingredient in concrete to be sold in metro Denver. The project awaits approval from the Colorado Department of Public Health and Environment.
The utility company expects to spend $24 million over the next 10 to 12 years to remove ash and treat contaminated groundwater, said Michelle Aguayo, an Xcel spokeswoman.
Officials at Boulder County Public Health are on board with the coal-ash cleanup, saying that recycling hazardous waste into a useful product is a proven solution. It would rid the site of a toxic substance and prevent anyone from trucking it to another community.
“That’s one reason we like this project — we’re not just putting this project on someone else. Another reason we like it is it will be a net greenhouse gas reduction,” said Bill Hayes, the county health department’s air quality program director. “We aren’t trucking it nationally. We are creating something that will be used locally and won’t have to be trucked in from thousands of miles.”
“Boulder County Public Health supports the project,” he said. “The beneficial use project will have global impacts. But there will be some risk with it.”
Xcel will be the first utility company in Colorado to initiate such a large-scale coal-ash cleanup after lithium and selenium leaked into groundwater and seeped toward wells used for drinking water on nearby properties.
But there are millions of tons of coal ash in other landfills and ponds around Colorado, and almost all of those sites are leaching pollutants into groundwater.
Over the years, public reporting of coal-ash contamination has been inconsistent because there was no regulation of the waste before 2015. Even after that, utility companies were only required to report monitoring results from landfills that were still in use — and those documents can be hard to find and difficult to understand.
Then, last year, the Biden administration expanded those reporting requirements to all waste disposal sites, although nothing has yet resulted from that rule change.
In 2022, two environmental organizations compiled a list of coal-ash waste sites across the United States, using Environmental Protection Agency reports, and their research identified 12 known coal ash locations in Colorado.
Earthjustice and the Environmental Integrity Project estimated that over the decades 14 Colorado power plants created more than 1.7 million tons of ash per year that went into landfills and retention ponds, according to their 212-page report.
The report placed three of Colorado’s coal-ash waste sites among the 50 most contaminated sites in the United States.
While Xcel has a plan to remove coal ash at the old Valmont station, environmentalists say it is unlikely that most utility companies will clean their sites unless forced by federal or state regulators, or if sued by impacted communities. Utility companies have a track record of doing the minimum amount required under the EPA’s Coal Combustion Residuals rules, said Abel Russ, senior counsel with the Environmental Integrity Project.
“They find ways to formally comply with the rule but not do much with cleanup because it’s expensive and they don’t want to spend the money,” Russ said.
Xcel’s cleanup project at Valmont comes as the Trump administration shows little appetite for enforcing existing coal-ash disposal rules, as the president and EPA Administrator Lee Zeldin push their “Powering the Great American Comeback” agenda, which prioritizes coal as a leading source of energy in the country.
On Thursday, a Republican-controlled House environmental subcommittee held a hearing to review coal-ash regulations and to discuss whether or not “government red tape and bureaucracy can stifle innovation surrounding the use of coal ash,” according to an announcement of the hearing.
Environmental Protection Agency Administrator Lee Zeldin testifies before the House Committee on Energy and Commerce Subcommittee on Environment in the Rayburn House Office Building on May 20, 2025, in Washington, D.C. (Photo by Kevin Dietsch/Getty Images)In Colorado, utility companies are phasing out coal-burning power plants as the state strives to reduce its greenhouse-gas emissions and pivot toward renewable energy such as wind and solar. Those companies will continue to produce coal ash until that happens. Meanwhile, the retention ponds and landfills that have held the ash for decades are not going away.
For example, Tri-State Generation and Transmission Association’s ash disposal facility near its Nucla Station in Montrose County received waste from 1987 until 2019, when the coal plant was retired. The company reported last year that 4.8 million tons of coal ash are in a landfill, and that the electric cooperative continues maintenance at the waste site.
Last year, Tri-State said it had taken steps to prevent erosion, including adding riprap along the perimeter and building a 1.5-foot-tall berm, according to the company’s 2024 inspection report.
The Valmont Power Station on North 63rd Street in Boulder operated as a coal-fired electricity generation station for almost a century, until it was converted to a natural-gas-powered station in September 2017. During that time, Xcel dumped its coal ash — also known as coal combustion residuals — into three ponds and a landfill.
In 2020, Xcel’s groundwater monitoring detected lithium and selenium leaching from a 60-acre landfill that was in operation from 1993 until 2017. That led the company to come up with a plan to remove the ash from the site and stop the leaks.
But it’s been a long process.
Xcel submitted its engineering and design plan earlier this year to explain how the cleanup will work. That plan is still under review by the state health department’s Hazardous Materials and Waste Management Division and will be subject to public comment once preliminary approval is given.
The company also must apply for a permit to emit pollutants into the air during the cement-making project, and that must also be approved by the state.
Work cannot start until those approvals have been given. Still, Xcel says it will begin in 2026.
A national problem
Nationally, 5 billion tons of coal ash are estimated to have been created by coal-powered electricity plants since the late 1800s, said Lisa Evans, senior counsel with Earthjustice, a nonprofit environmental law group.
Coal ash is the second-largest industrial waste stream in the country, accounting for 70 million tons pouring into landfills and retention ponds every year, Earthjustice research found.
“If you ask if there’s a big problem with coal ash in the U.S., the answer is yes because coal ash was mismanaged for decades,” Evans said.
Hazardous chemicals found in coal ash include arsenic, boron, cobalt, chromium, lead, lithium, radium and selenium. Those chemicals are known to cause an increased risk of various cancers, heart and thyroid disease, respiratory illnesses and neurological problems.
Lithium is a naturally occurring metal and has various commercial uses, including as a material used in batteries. The EPA has placed lithium on a list of priority contaminants in drinking water, but has not established regulations on how much is an acceptable minimum level. Lithium has been known to cause renal and neurological problems in people.
Selenium is also a naturally occurring metal and has useful purposes, including as an essential nutrient at low levels. The EPA has established a maximum level for that metal, which can damage the liver, kidneys, nervous system and circulatory system, and cause hair loss.
Coal-ash disposal in the United States was unregulated until after the December 2008 Kingston TVA coal ash spill in eastern Tennessee.
In that disaster, a dike used to contain coal ash broke near the Tennessee Valley Authority’s Kingston Fossil Plant in Roane County, dumping 5.4 million cubic yards of toxic coal ash into nearby water, including the Emory and Clinch rivers, and contaminating more than 300 acres of land. It took more than six years to clean the mess from rivers and streams, and private property. Hundreds of workers were sickened — and dozens died — from exposure to arsenic, lead, mercury and radium that was in the coal ash.
Fly ash is loaded into plastic-lined rail cars at the Tennessee Valley Authority's Kingston Fossil Plant on Thursday, Dec. 17, 2009, in Kingston, Tennessee. (AP Photo/Wade Payne)“That was just so dramatic that it focused everyone’s attention on it. It reminded everyone that it’s a huge waste stream,” Russ said.
When Americans first started burning coal to provide electricity, no one thought about the ash byproduct left over after the coal burned. The ash was dumped in unlined lagoons and landfills without much thought.
“It’s the sheer volume of it and the concentration of heavy metals in it,” Russ said. “They didn’t wrap their heads around it until it was too late.”
The EPA established the first rules for coal-ash management in 2015 in the wake of the Kingston disaster. The rules addressed the risks associated with coal-ash disposal, including leaks into groundwater, dust blowing into the air and failures of barriers around landfills.
The federal government also began requiring record-keeping and reporting at active coal-ash landfills across the country, and the regulations allowed for the beneficial use of coal ash, which is what Xcel is planning for the Valmont Power Station in Boulder.
Those 2015 rules only applied to active landfills and excluded some of the oldest coal-ash ponds and landfills in the country. In 2024, the EPA, under President Joe Biden, tightened rules governing those older ponds and landfills that required monitoring for pollutants and cleanup.
However, the Trump administration has already signaled that it will not prioritize coal-ash enforcement, Evans said.
In March, Zeldin announced a plan to shift coal-ash regulation to the states with EPA support, and pledged to change the rules on compliance deadlines by the end of this year.
That means there will be uneven enforcement across the country, with coal-friendly states such as Wyoming and North Dakota becoming lax while other states, including Colorado, tackle the challenge, Evans said.
“Coal ash is like running on a treadmill. We gain ground and lose ground,” Evans said. “We made progress with Obama, and Trump tried to rescind it, but ended up just delaying. Then we got a new rule with President Biden to fill the gaps. And now the Trump administration wants to undo it.”
A Colorado problem
There are 12 known locations in Colorado where coal ash has been dumped, and those sites include 38 coal-ash ponds and landfills, according to a database maintained by Earthjustice. There could be other unknown sites where coal ash was stored long before any regulations existed, the environmental group says.
Those 12 sites are on the grounds of former or active coal-burning power plants, or nearby landfills, and are the responsibility of the utility companies that own them. It’s unclear exactly how much coal ash is buried in the ground in Colorado because of incomplete reporting.
Click to enlargeXcel is responsible for seven of the coal-ash waste sites in the state: the former Arapahoe Generation Station in Denver; the former Cameo Generation Station in Mesa County; the Cherokee Generation Station in Denver; the Comanche Generation Station in Pueblo; the Hayden Generation Station in Routt County; the Pawnee Generation Station in Morgan County; and Valmont.
The other sites in Colorado include: Colorado Springs Utilities’ Clear Spring Ranch Landfill, which holds waste from the Ray Nixon Power Plant and the former Martin Drake Power Plant; Tri-State Generation and Transmission Association’s Nucla Ash Disposal Facility, which holds waste from its former Nucla Station in Montrose County and its Craig Station in Moffat County; and the Platte River Power Authority’s Rawhide Energy Station in Larimer County.
Earthjustice also reported there is a coal-ash waste site at the former Martin Drake Power Plant in El Paso County, but there are no available reporting documents online and efforts to reach Colorado Springs Utilities were unsuccessful.
It is also unknown whether there is coal-ash waste associated with the former W.N. Clark Power Plant in Fremont County, which was decommissioned in 2012.
Earthjustice lists three Colorado coal-ash sites among the 50 most contaminated in the country because they have multiple pollutants exceeding EPA standards: Valmont is ranked 31st; Tri-State’s retired Nucla station is 39th; and Xcel’s Hayden Station is 44th.
While it is unclear exactly how much coal ash is buried in landfills and sitting in retention ponds across the state, a Denver Post review of available 2024 coal combustion residual inspection reports found more than 30 million tons at the various sites. No reports are available for landfills that were closed before 2015.
Xcel’s seven sites contain more than 19 million tons of coal ash, according to inspection reports the company posted online. However, not every Xcel disposal site has an updated report on the company’s coal-ash management website, in part because of the change in reporting rules for coal-ash sites. The Post found online reports missing for Arapahoe, Cameo, Cherokee and Pawnee’s north landfill sites.
Xcel declined to make its coal-ash managers available for interviews with The Post. Instead, Aguayo, the company’s Colorado spokeswoman, sent an emailed statement and referred the newspaper to the company’s website for any information on coal-ash management.
“Protecting our customers and the environment is a priority, and we have a strong record of environmental leadership,” Aguayo said in the statement. “We’re committed to responsibly managing impacts from our operations, including from prior coal plants, like Valmont.”
In the past three years, Xcel has been cited twice by the EPA for failures to comply with coal-ash regulations.
Xcel’s Cherokee Generating Station transitioned to a natural-gas-fired power plant in 2017 and closed five dumpsites, including a retention pond, on the property. But closing a coal-ash disposal location does not mean the coal ash is removed. Rather, no more waste is dumped there.
Xcel was fined $134,500 in September after lithium was discovered leaking from its Cherokee plant, identifiable by its red-and-white smokestack visible from north Denver. The EPA cited the company for failing to adequately prepare groundwater monitoring reports, failing to meet groundwater monitoring performance standards, failing to accurately represent readings in groundwater quality, and failing to use the most effective statistical methods to analyze groundwater data, according to the agency’s consent agreement.
Xcel agreed to correct its missteps, according to the consent agreement between the company and the EPA.
The utility is still assessing how to treat the lithium plume, said Lauren Whitney, a state health department spokeswoman. Xcel is evaluating two solutions and will hold a public meeting before selecting a method and starting work.
But that’s not the largest fine Xcel has paid for coal-ash violations.
In 2022, the EPA penalized the company for failing to comply with regulations on the disposal of coal ash and not properly monitoring groundwater at its Comanche station in Pueblo. The company paid $1 million to settle with the federal government.
That site is releasing cobalt into the groundwater.
Xcel has identified the plume, tested the groundwater and is putting together a remediation strategy, Whitney said.
Between August 2024 and February, the remediation strategy included injecting a treatment reagent into six injection wells using an EPA-approved method, Whitney said. Wells near the plume did not have cobalt levels that exceeded the drinking water standards.
Meanwhile, Xcel continues to dump coal ash into a landfill in Pueblo until the coal plant is decommissioned, no later than Dec. 31, 2030. As of 2024, about 4.9 million tons of coal ash are in the ground at Comanche, according to the most recent inspection report.
Cleaning up Valmont
Valmont Station will be the first site in Colorado where Xcel plans to convert coal ash into Portland cement, an ingredient used to make concrete. And it is the only site with such a massive cleanup in the company’s plans, Aguayo said.
The company has contracted with Charah Solutions, a Kentucky-based company that specializes in coal-ash management and cleanup. Charah has hired Geocycle, an industrial waste management company, to help with the project, Aguayo said in the utility’s statement.
Charah is expected to process about 2 million tons of ash over 10 years to remove the hazardous waste.
Charah and Geocycle use a proprietary system to recycle the ash into cement. It involves a mobile kiln that would be set up on the Valmont property, and the companies would use a baghouse — an industrial dust collector — to prevent harmful air emissions, Aguayo said.
Charah will only excavate the amount of ash that its workers intend to process in one day to avoid leaving excess ash on the ground that could blow into the community at night when the work stops, she said. The equipment is enclosed to manage dust, and the noise it makes is similar to Valmont’s normal operations.
The cement created onsite will be sold and used in the Denver market, Aguayo said.
“This project provides large-scale environmental benefits by eliminating the need to mine new raw materials for Portland cement and by eliminating the need for cross-regional transport of Portland cement and/or concrete to Denver’s local market,” her statement said.
Operations will run during daylight hours, seven days a week. Work will stop when wind gusts exceed 55 mph or sustained winds exceed 40 mph, according to the company’s engineering and design plan.
Once the ash is removed, the contractor will grade the area and put down clean soil and grass seed. Any ash that is not suitable for recycling will be placed in a specific area of the landfill, and then the landfill will be closed.
Hayes, the air quality manager at Boulder County Public Health, said he is most concerned about how much dust will flow into the air once the project starts. The engineering and design plan calls for dust control systems but lacks details.
“That’s what I’m really waiting to see are the controls we want to see in that dust control plan,” Hayes said. “The dust concerns from start to finish are when they are excavating the landfill sites.”
Hayes hopes more of those details will be included in the company’s air-pollution permit. He wants the state health department to require continuous air-quality monitoring at the site, but so far, the state has not agreed to consider it once the air permit is filed.
“CDPHE says they’ve never required it in an air permit,” Hayes said. “I said, ‘Yeah, but we’ve never issued an air permit for a coal-ash landfill project.’ This is a unique and novel project, and we just don’t need to go with what we’ve done in the past.”
Hayes said he’s not optimistic that a monitoring requirement will be included in the air permit, so he is searching for outside funding to pay for it.
“In our current climate, getting funding for air monitoring is proving to be a little challenging,” he said. “Federal grants that used to be available for that are dwindling and going away.”
But the air quality problem at a coal-ash landfill only occurs once a company starts excavating the material.
The more critical problem at most coal-ash waste sites is the groundwater contamination.
“It’s a huge problem. We’ve been burning coal since the early 1900s,” said Evans, with Earthjustice. “The ash was not regulated until 2015, so billions of tons of coal ash have been dumped in pits and ponds and used as fill across the United States. Almost every state had a coal-burning power plant.”
For years, companies were allowed to dump the ash without lining the landfills. More than 90% of coal-ash waste sites have contaminated groundwater above federal safety standards, she said.
“It’s not an exaggeration to say that whenever you dump coal ash, you’re going to get water contamination,” Evans said.
At the Valmont Station, Xcel has monitored groundwater with a network of wells that the utility drilled in the area, said Carl Job, a water quality specialist with Boulder County Public Health. Those wells detected elevated levels of lithium and selenium in a plume moving north and east of the property, and the plume was moving toward nearby drinking water wells.
The Valmont Power Station, as seen from nearby Legion Park on June 17, 2025, in Boulder, Colorado. (Photo by RJ Sangosti/The Denver Post)Xcel filed an ash landfill remedy selection report, which proposes a cleanup method, in May with the state health department. The report said two plumes were creeping out of the landfill. The first plume contains elevated concentrations of lithium and selenium, while the second plume exceeds lithium levels mandated by the EPA.
“These plumes are not adversely impacting drinking water in the area, and the groundwater will continue to be monitored to ensure ongoing protection of human health in the area until remedy completion,” the report stated. “There are also no public drinking water supplies in the vicinity of the impacted groundwater.”
The contaminated plumes are not a threat to most Boulder residents, who get their water from the city system, Job said. The real concern surrounds the few wells nearby where people get their drinking water, which are not as regulated as public water systems.
Only one well has shown higher levels of lithium contamination, and Xcel is providing an alternate source of water, said Erin Dodge, Boulder County Public Health’s water quality program coordinator.
The plumes are not impacting Boulder Creek or South Boulder Creek, she said.
Groundwater remediation is proceeding under a compliance order from the state, Whitney said. Xcel has submitted a proposal for treating the groundwater, and it is under review by the state and Boulder County. Once it is approved, Xcel will submit a design plan for the state health department to review.
Xcel is proposing to use reverse osmosis, which is a proven method for cleaning water. That system will extract groundwater through wells and collection trenches and truck it off-site for treatment, the report said.
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Meanwhile, there is no other long-term plan for removing the millions of tons of coal ash buried in Colorado.
Some utilities, such as the Platte River Authority, sell some ash for beneficial reuse. Platte River sells ash to architectural block manufacturers and to liquid-waste disposal facilities, according to its company website.
Officials at the Colorado Department of Public Health and Environment say they are committed to making sure coal ash does not contaminate groundwater.
The state regularly monitors coal-ash waste sites, said Tracie White, director of the health agency’s hazardous waste division. And Valmont is of particular interest because of the size of its ash reuse project.
“We are committed to making sure coal ash landfills in Colorado are protective of human health and the environment,” White said. “At Valmont Station, our team is closely reviewing the proposed cleanup remedy to ensure it meets all state regulations and prevents further impacts to groundwater. We regularly monitor these sites to track, trace, and treat potential contamination, and we work in partnership with local communities throughout the process.”
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