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Sarah Kanouse, An abandoned mine overlooks the Dolores river in Western Colorado, 2014,

Issue Brief

Abandoned Mines

Long after the extraction of uranium ceases, abandoned mines continue to endanger the communities that surround them. U.S. Department of Energy, Office of Legacy Management, “Defense-Related Uranium Mines Location and Status Topic Report,” LMS/S10693, August 2014, https://www.energy.gov/sites/prod/files/2017/07/f35/S10693_LocStatus.pdf; Jonathan Wood, “Prospecting for Pollution: The Need for Better Incentives to Clean up Abandoned Mines,” Public Lands Report, August 2020, Property and Environment Research Center, Bozeman, MT, https://www.perc.org/wp-content/uploads/2020/02/prospecting-for-pollution-abandoned-mines.pdf.Colorado contains approximately 23,000 of the nation's estimated 500,000 abandoned mines, including over 1,539 uranium mines. Many uranium mines predate environmental regulations implemented in the 1970s. Prior to this era, mining companies could simply vacate and abandon mine sites, leaving behind open pits, radioactive soil heaps, and other hazardous materials. Under the Colorado Mined Land Reclamation Act (1976), mining companies are now required to reclaim sites once their operations conclude. However, many companies leave mines in perpetual standby, thereby avoiding regulations. Regardless of their legal status, abandoned and inactive mines present numerous dangers. Physical hazards, such as mine shafts, quarries, and dilapidated structures, injure dozens of people every year. Environmental pollution, while more difficult to quantify, poisons humans and ecosystems alike. These factors represent the hidden costs of mining—costs the public continues to bear even as mining companies have earned their profits and moved on.

Uranium mining has not always been a tightly controlled industry. Uranium had been used in colored glass, ceramics, and enamels from around the 1830s to 1940s.Uranium ore had little commercial use before the discovery of fission, but in 1898 Marie and Pierre Curie discovered that it could be processed to produce radium. For two brief decades, from the mid-1910s until the mid-1920s, radium was the most valuable material in the world, leading to an initial mining boom in Utah and Colorado. At the height of the bubble, mining operations in these states Stephen S. Hart and Eric Twitty, "Colorado's 'Lost' Radium Boom: Early 20th Century Mining and Processing Landscapes on the Colorado Plateau and in Denver," accessed July 30, 2020, https://montrosecounty.granicus.com/MetaViewer.php?view_id=2&clip_id=141&meta_id=10184.extracted over 4,000 tons of uranium ore a year. U.S. productions collapsed suddenly in 1923 after the discovery of uranium deposits in the Belgian Congo (now the Democratic Republic of Congo). Hundreds of Colorado mines were abandoned, although it is difficult to determine a precise number since many of these early mines were small operations run by a few individuals. Poor historical records pose challenges for land management agencies and personnel attempting to locate abandoned mines. Furthermore, federal agencies often overlook these early mine sites and instead prioritize remediating the larger and far more numerous uranium mines developed during the mid-twentieth century uranium boom.

The Manhattan Project revived demand for uranium in the 1940s, and the Atomic Energy Commission (AEC) expanded production for much of the Cold War with lucrative contracts, guaranteed prices, and minimal regulation. Annual production ballooned to just over 35 million pounds in 1960, leading to the creation of modern boom towns throughout the Colorado Plateau. New Mexico and Arizona dominated the industry, but Colorado produced 71 million pounds of uranium concentrate from 1948 until 1976, much of it mined in the Uravan Mineral Belt that stretches from Slick Rock to Grand Junction. Over 1,200 mines operated in this area alone during these three decades. The AEC ended uranium subsidies in 1971, but the growing nuclear energy sector kept prices high for the next decade. At the height of the uranium boom in 1980, the U.S. was producing over 21,850 tons of uranium concentrate annually. Quickly, however, rising international competition in the uranium market, growing stockpiles, and mounting concerns over nuclear power (stimulated in part from the Three Mile Island disaster in 1979) led to decimated uranium prices. Within five years, eighty percent of the country’s mines had suspended operations and annual production dropped to just 5,499 tons. It would never recover.

The sudden collapse led to foreclosures, bankruptcies, and hundreds of abandoned mines. The Department of Energy (DOE) has identified 1,539 abandoned uranium mines in Colorado that were connected to the AEC, but there are likely more. Many companies retained property rights and simply left sites idle. Others sold properties without removing buildings or mine features. The shifting ownership, uncertain legal status, and sheer scale of Colorado’s uranium industry means that mine sites are often difficult to identify. U.S. Department of Energy, Office of Legacy Management, “Defense-Related Uranium Mines Location and Status Topic Report,” LMS/S10693, August 2014, https://www.energy.gov/sites/prod/files/2017/07/f35/S10693_LocStatus.pdf.The DOE has records of 116 mines in Colorado with unknown or unspecified locations. This is especially problematic since abandoned mines present unknown dangers to surrounding ecosystems and human communities.

Abandoned mines pose unique physical hazards, among them, mill tailings and remnant buildings, leftover equipment, precipices, pools, and even gases that could potentially cause injury or death. Older mines likely had less stringent safety standards during their construction, and time has only increased the risks. Historical mines are often dilapidated and structurally unsound, with buildings, mine shafts, and other structures that may collapse if entered or climbed on. Open-pit highwalls could also collapse, but even stable ones and more well-maintained structures pose fall risks. Former mining areas, especially with unstable spoil piles, may experience landslides. Other hazards are more subtle. Mine shafts may be hidden under debris or rotten floor boards. Pools and water-filled quarries may be unexpectedly deep, or contain hidden ledges and sunken equipment that could trap anyone who intentionally or accidentally enters the mine. Bureau of Land Management, “Dangers at Abandoned Mines...Can Kill You,” BLM/WO/GI-13/009+3720, accessed June 22, 2021, https://www.blm.gov/sites/blm.gov/files/uploads/AML_PUB_DangersAtAbandonedMines.pdf.Drowning is actually the most common cause of death at abandoned mines. Underground shafts or tunnels can prove unexpectedly confusing and difficult to navigate, and trespassers may become lost or trapped. Worse yet, mines are not ventilated, leading to oxygen-deficient areas which cause those who enter to faint and asphyxiate. There may also be pockets of toxic gasses like radon. Old explosives and harsh chemicals pose additional dangers. Even professional miners fall victim to these invisible threats.

The prevalence and accessibility of abandoned mine sites compound their hazards. Around three-fourths of abandoned mines are located on federal lands, which poses significant risks to the public who may stumble upon them accidentally. Older mine sites rarely have signage or fencing, and may be so overgrown with vegetation that hikers, bikers, and other recreationists do not see hazards until it is too late. Many mines are also close to roadways, which is dangerous for at least two reasons. First, it exacerbates the risks of automobile accidents. For example, Mitchell Byars, “Boulder Man Faces Vehicular Homicide, DUI Charges in Crash That Killed 2,” Boulder Daily Camera, June 16, 2016, https://www.dailycamera.com/ci_30024919/boulder-dance-instructor-faces-vehicular-homicide-dui-charges.in 2016 two teenagers died after their car went off the road and crashed into a 12-foot mine shaft in Boulder County. Second, tourists and other visitors may be tempted to explore mine sites near popular roadways used for sightseeing, such as the Million Dollar Highway between Silverton and Ouray. Every year, thrill seekers intentionally enter mine shafts, underestimating the dangers that await. This was the case with a teenager Dillon Thomas, “Teen Trapped in Old Mine Shaft Rescued,” CBS4, December 7, 2017, https://denver.cbslocal.com/2017/12/07/rescue-mine-shaft-golden/.who became trapped in a mine outside of Golden, Colorado in 2017. He was rescued after three hours, but others are not so lucky. According to The Durango Herald, “Jonathan Romeo, “Agencies to Close 25 Abandoned Mines on Alpine Loop,” The Durango Herald, September 29, 2018, https://www.the-journal.com/articles/agencies-to-close-25-abandoned-mines-on-alpine-loop/.From 2001 to 2017, five people died in abandoned mine accidents in Colorado." To address these hazards, Colorado’s Division of Reclamation, Mining, and Safety (DRMS) Colorado Department of Natural Resources, Division of Reclamation, Mining and Safety, “Inactive Mine Reclamation Program,” July 11, 2019, https://www.colorado.gov/pacific/drms/inactive-mine-reclamation-program.seals approximately 300 mines every year, but they have a long way to go with thousands of abandoned mines on Colorado’s public lands.

Physical hazards are largely immobile: they endanger anyone who comes near them, but have a limited geographic impact. The same cannot be said for environmental pollution. Abandoned mines pollute entire watersheds through acid mine drainage, heavy metal leaching, and radiation. Acid mine drainage, or AMD, occurs when mining exposes metal sulfides such as pyrite to the water or air. The sulfides slowly dissolve, leading to the formation of sulfuric acid, an extremely corrosive acid that destroys the natural balance of streams and rivers. Fish and other aquatic species cannot survive in highly acidic streams, and the water is not safe for human or animal consumption. Furthermore, sulfuric acid dissolves the surrounding rock, leaching heavy metals like arsenic, mercury, lead, or cadmium into water. These metals dissolve naturally, but AMD intensifies the process, leading to dangerously high concentrations. Under these circumstances, heavy metals disrupt the biological processes of microorganisms, plants, animals, and even humans. They increase the toxicity of soil and water, leading to slower growth and decomposition rates. They also bioaccumulate, meaning that they build up over time and move up the food chain. If humans are exposed to high concentrations of heavy metals, they may develop problems with their central nervous, endocrine, reproductive, or cardiovascular systems. Other health complications include Godwill Azeh Engwa, Paschaline Udoka Ferdinand, Friday Nweke Nwalo, and Marian N. Unachukwu, “Mechanism and Health Effects of Heavy Metal Toxicity in Humans,” in Poisoning in the Modern WorldNew Tricks for an Old Dog?, eds. Ozgur Karcioglu and Banu Arslan, IntechOpen, June 19, 2019, https://doi.org/10.5772/intechopen.82511.kidney and liver failure, neurological damage, and various types of cancer.

Radiation functions differently, but the end result is the same: irreparable damages. Uranium mining produces large amounts of waste rock, much of it radioactive, even if the uranium content is minimal. The milling process produces more concentrated waste, in the form of solid mine tailings or liquid raffinates, both of which are highly radioactive and must be stored securely. Areas around mines and especially mill sites continue to emit radionuclides long after production ceases. Radioactive particles dissolve in water or are carried by the wind, infecting the environment around them. They enter into the food chain and water table, slowly accumulating in vegetation, wild animals, livestock, and human bodies. Radiation damages DNA, leading to genetic mutation and infertility. In humans and other mammals, radiation contributes to cancer, organ failure, and cardiovascular disease.

The large number of abandoned mines in Colorado and their extensive environmental hazards threaten human health. Unfortunately it is difficult to quantify or accurately measure the damage caused by abandoned mines. Living near an abandoned mine may lead to cancer, but this is difficult to prove. For example, in 2009, former residents of Uravan, now a Superfund site, sued a mining company for causing various cancers that they linked to local mine operations. The judge rejected the lawsuit Dick Kamp, “Uravan Lawsuit: Health Hazards from the Past versus Today,” Montrose Daily Press, September 13, 2009, https://www.montrosepress.com/news/uravan-lawsuit-health-hazards-from-the-past-versus-today/article_df5b0ef3-6339-58c0-b2ba-b451e80caa67.html.“on the grounds that the plaintiffs could not demonstrate that their cancers and other illnesses would not have occurred ‘but for’ the ionizing radiation from the mill and mines.” Despite the lack of “factual causation” determined in this specific case, human and environmental health advocates continue to seek correlations between uranium mines, mills, disposal sites, and cancer clusters. There is widespread evidence of environmental pollution: more than 1,800 miles of Colorado’s waterways are impaired due to mine-related contaminates, and theColorado Department of Public Health and Environment, and Colorado Department of Natural Resources, “Colorado Abandoned Mines Water Quality Study,” June 2017, http://www.colorado.gov/cdphe/wq-mining. DOE estimates that Colorado has 5,000 tons of uranium ore exposed on surface spoil heaps. This certainly affects Colorado’s citizens, even if it is impossible to quantify the exact impact.

In addition to routine environmental pollution, abandoned mines bear the threat of catastrophic contamination. Many mine areas containing radioactive waste ponds and spoil heaps are over forty years old. If any of this aging infrastructure should fail, the results would be disastrous. For comparison, when the disposal pond of New Mexico’s Church Rock uranium mill failed in 1979, Anita Moore-Nall, “The Legacy of Uranium Development on or Near Indian Reservations and Health Implications Rekindling Public Awareness,” Geosciences 5, no. 1 (2015): 15–29, https://doi.org/10.3390/geosciences5010015.it released over 1,000 tons of solid radioactive mill waste and 93 million gallons of acidic, radioactive tailings solution into the Rio Puerco river, a tributary of the Colorado. Outside of the atomic bomb tests, this was likely the largest single release of radioactive contamination ever to take place in the United States. There have been no long-term health studies or monitoring at the Church Rock site, but Chris Shuey and Melinda Ronca-Battista, “Report of The Church Rock Uranium Monitoring Project (Crump), 2003-2007," May 2007, http://www.sric.org/uranium/docs/CRUMPReportSummary.pdf.a 2007 study found significantly higher levels of background radiation and half the surrounding water sources unfit for domestic use, including cooking, washing, or irrigation.

Although Colorado has not seen any disasters as severe as the one at Church Rock, it has experienced smaller uranium spills and some major accidents related to abandoned hard metal mines. Bruce Finley, “Cotter’s Defunct Uranium Mill Line Leaks 1,800 Gallons near Cañon City,” Denver Post, November 30, 2015, https://www.denverpost.com/2015/11/30/cotters-defunct-uranium-mill-line-leaks-1800-gallons-near-caon-city/.At least five spills over the last decade discharged more than 26,000 gallons of contaminated water at the former Cotter Mill, located outside of Cañon City and now an EPA Superfund site. While significant, this pales in comparison to the damage caused by the Gold King Mine spill, one of Colorado’s worst environmental disasters. During remediation work at the abandoned gold mine in 2015, EPA contractors accidentally destroyed a barrier, releasing 3 million gallons of contaminated water and nearly 540 tons of heavy metals into Cement Creek, a tributary of the Animas River. The spill caused an estimated $2 billion in economic damage, but the full environmental impact is impossible to determine. Had the Gold King Mine contained uranium ore, the results would have been far worse. Until the Cotter Mill and other inactive uranium mine sites are comprehensively remediated, there is always the risk of a larger spill. 

Hypothetically, abandoned mines should be a diminishing problem. Colorado passed the Mined Land Reclamation Act in 1976, mandating reclamation standards and creating a board to oversee their enforcement. The state also established an Inactive Mine Reclamation program in 1980 to address the hazards and environmental problems posed by legacy mines. Unfortunately, mining companies have developed a strategy for leaving mines inactive while avoiding regulations: standby status. Both state and federal law allow uranium mines to halt production in response to fluctuating prices. Mark Olalde and Joe Yerardi, “While ‘Zombie’ Mines Idle, Cleanup and Workers Suffer in Limbo,” Center for Public Integrity, September 4, 2019, https://publicintegrity.org/environment/while-zombie-mines-idle-cleanup-and-workers-suffer-in-limbo/.According to Colorado law, companies can only remain in standby for ten years before they must resume mining or begin reclamation, but mining companies use legal loopholes to avoid this stipulation. U.S. Department of Energy, Office of Legacy Management, “Uranium Leasing Program,” Energy.gov, accessed December 6, 2020, https://www.energy.gov/lm/services/property-management/uranium-leasing-program.There are 29 actively leased, permitted uranium mines in Colorado, but none of them are currently bringing uranium to market. Mining companies maintain that they will resume production once prices increase, even as machinery rusts and radioactive dust is carried off on the wind. The Van 4 mine near the lower Dolores River has not been active since 1989. Jim Mimiaga, “Colorado Court of Appeals Rules for Mine Cleanup,” The Journal, November 21, 2019, https://www.the-journal.com/articles/colorado-court-of-appeals-rules-for-mine-cleanup/.In 2019—thirty years later—the Colorado Court of Appeals finally ruled that the owners must begin reclamation. Many activists hope this ruling will set a precedent that forces other standby mines to initiate cleanup. Holding the current industry accountable is a critical step, but numerous physical and environmental hazards scattered across the Colorado landscape were created by companies long gone. It will take the combined effort of federal and state agencies, local governments, private industry, activists, experts, and local citizens all working together to address the hidden costs of Colorado’s nuclear past.


Bureau of Land Management. “Dangers at Abandoned Mines...Can Kill You.” BLM/WO/GI-13/009+3720. Accessed April 3, 2021.

Colorado Department of Natural Resources, Division of Reclamation, Mining and Safety. “Inactive Mine Reclamation Program.” July 11, 2019. Accessed March 23, 2021.

Colorado Department of Public Health and Environment, and Colorado Department of Natural Resources. “Colorado Abandoned Mines Water Quality Study-Data Report.” June 2017. Accessed March 23, 2021.

Finley, Bruce. “Cotter’s Defunct Uranium Mill Line Leaks 1,800 Gallons near Cañon City.Denver Post, November 30, 2015. Accessed March 23, 2021.

Frosch, Dan. “A Fight in Colorado Over Uranium Mines.The New York Times, April 16, 2013. Accessed April 4, 2021.

Mimiaga, Jim. “Colorado Court of Appeals Rules for Mine Cleanup.The Journal, November 21, 2019. Accessed January 13, 2023.

Moore-Nall, Anita. “The Legacy of Uranium Development on or Near Indian Reservations and Health Implications Rekindling Public Awareness.Geosciences 5, no. 1 (2015): 15–29.

Olalde, Mark, and Joe Yerardi. “While ‘Zombie’ Mines Idle, Cleanup and Workers Suffer in Limbo.” The Center for Public Integrity, September 4, 2019. Accessed March 23, 2021.

Romeo, Jonathan. “Agencies to Close 25 Abandoned Mines on Alpine Loop.The Durango Herald, September 29, 2018. Accessed January 13, 2023.

U.S. Department of Energy, Office of Legacy Management. “Defense-Related Uranium Mines Location and Status Topic Report.” LMS/S10693, August 2014. Accessed March 23, 2021.

U.S. Department of Energy, Office of Legacy Management. “Uranium Leasing Program.Energy.gov. Accessed December 6, 2020.

Wood, Jonathan. “Prospecting for Pollution: The Need for Better Incentives to Clean up Abandoned Mines.PERC Public Lands Report. February 2020. Accessed March 23, 2021.

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