Church Rock uranium mill spill

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United Nuclear Corp. Church Rock
Superfund site
United Nuclear Corporation Church Rock Uranium Mill.jpeg
The United Nuclear Corporation Site near Church Rock in McKinley County, New Mexico
CityGallup, New Mexico
StateNew Mexico
Coordinates35°39′03″N 108°30′23″W / 35.65083°N 108.50639°W / 35.65083; -108.50639Coordinates: 35°39′03″N 108°30′23″W / 35.65083°N 108.50639°W / 35.65083; -108.50639
United Nuclear Corp. Church Rock is located in New Mexico
United Nuclear Corp. Church Rock
United Nuclear Corp. Church Rock
2,133 m (6,998 ft)
ContaminantsMetals, radionuclides
United Nuclear, Inc.
List of Superfund sites

The Church Rock uranium mill spill occurred in the US state of New Mexico on July 16, 1979, when United Nuclear Corporation's Church Rock uranium mill tailings disposal pond breached its dam.[1][2] Over 1,100 tons of solid radioactive mill waste and 94 million gallons of acidic, radioactive tailings solution flowed into the Puerco River through Pipeline Arroyo. An estimated 1.36 tons of uranium and 43 trillion picocuries of gross-alpha contaminants traveled 80 miles (130 km) downstream[3] to Navajo County, Arizona and onto the Navajo Nation.[2] The mill was located on privately owned land approximately 17 miles north of Gallup, New Mexico, and bordered to the north and southwest by Navajo Nation Tribal Trust lands.[4] Local residents, who were mostly Navajo peoples, use the Puerco River for drinking water from wells, for irrigation and livestock and were not warned immediately of the toxic dangers from the spill.[2]

The accident is frequently described as having released more radioactivity than the Three Mile Island accident that occurred four months earlier and was the largest release of radioactive material in U.S. history.[2][5][6][7] The spill contaminated groundwater and rendered the Puerco unusable by local residents.

The governor of New Mexico Bruce King refused the Navajo Nation's request that the site be declared a federal disaster area, limiting aid to affected residents.[8] The nuclear contamination event received less media coverage than that of Three Mile Island. Although the spill occurred in a lightly populated, rural area[9] the deadly results from nuclear radiation well known to scientists and the federal government since uranium mining began on Navajo Nation and Lakota Nation lands in 1944. In 1951, the U.S. Public Health Service began human testing experiments on long term effects from nuclear radiation, using Navajo miners as non-consenting test subjects, in Uranium mining and the Navajo people. Some scholars suggest there were elements of class and racism to the neglect as well, since it affected primarily poor Native Americans.[6] Other scholars cite Church Rock's avoidable nuclear spill as another instance of state sponsored bio-terrorism targeting Indigenous peoples.[10]

In 2003 the Churchrock Chapter of the Navajo Nation began the Church Rock Uranium Monitoring Project to assess environmental impacts of abandoned uranium mines; it found significant radiation from both natural and mining sources in the area.[11] The EPA National Priorities List currently includes the Church Rock tailings storage site, where "groundwater migration is not under control."[12]

Dam failure[edit]

At around 5:30 am on July 16, 1979, a previously identified crack opened into 20-foot breach in the south cell of United Nuclear Corporation's Church Rock temporary uranium mill tailings disposal pond, and 1,100 tons of solid radioactive mill waste and approximately 93 million US gallons (350,000 m3) of acidic, radioactive tailings solution flowed into Pipeline Arroyo, a tributary of the Puerco River.[2][6][13][14] Warnings of an impending spill had been ignored by the state and by United Nuclear Corporation.[15] Though the uranium mill only bordered the Navajo Nation, the tailings spilled onto the Navajo Nation as they flowed down the Puerco River.[2]

The 20-foot breach in the tailings dam formed around 5:30 am on the morning of July 16, 1979.[2]

The tailings solution had a pH of 1.2[16] and a gross alpha particle activity of 128 nanocuries (4.7 kBq) per liter, and contained radioactive uranium, thorium, radium, polonium, metals including cadmium, aluminium, magnesium, manganese, molybdenum, nickel, selenium, sodium, vanadium, zinc, iron, lead, and high concentrations of sulfates.[17] The contaminated water from the Church Rock spill traveled 80 miles (130 km) downstream, through Gallup, New Mexico, and reached as far as Navajo County, Arizona. The flood backed up sewers, affected nearby aquifers, and left stagnating, contaminated pools on the riverside.[6][18][19]


At 6:00 am, a United Nuclear Corporation employee noticed the breach and suspended further discharge of tailings solution to the holding pond.[6] By 8:00, a temporary dike had stopped the flow of residual tailings solution.[6]

Several days after the spill, the Indian Health Service and the Environmental Improvement Division of New Mexico warned local residents over the radio and with signs written only in English to not drink from, water livestock at, or enter the Puerco River. Many Navajo people in the area speak only Dine, an Athabaskan language spoken by 150,000 people in the Navajo Nation.

The states of Arizona and New Mexico failed to make their residents immediately aware of the dangers of radiation.[20][21] United Nuclear Corporation employees were dispatched to warn Navajo-speaking residents downstream in accordance with a state contingency plan, but not until a few days after the spill.[5][22] The Navajo Nation asked the governor of New Mexico, Bruce King, to request disaster assistance from the US government and have the site declared a disaster area, but he refused, which limited disaster relief assistance to the Navajo Nation.[6]

Although the New Mexico Environmental Improvement Division said the spill's "short-term and long-term impacts on people and the environment were quite limited"[23], ponds of uranium contaminated water lined the Puerco River and seeped into wells. United Nuclear denied claims that the spill caused livestock deaths, eventhough the Navajo economy which was dependant on the sale of mutton was decimated. The company said in a statement issued by an attorney, "We just don't know of any substance to those claims. Some people aren't going to be satisfied no matter how thoroughly you show it."[23] Navajo Tribal Council's vice president Frank Paul said of the worst spill in US history, "Somehow, United Nuclear Corporation was permitted to locate a tailings pond and a dam on an unstable geologic formation. Somehow, UNC was allowed to design an unsafe tailings dam not in conformance to its own design criteria. Somehow, UNC was permitted to inadequately deal with warning cracks that had appeared over two years prior to the date the dam failed. Somehow, UNC was permitted to continue a temporary dam for six months beyond its design life. Somehow, UNC was permitted to have a tailings dam without either an adequate contingency plan or sufficient men and material in place to deal with a spill. Somehow, UNC was permitted to deal with the spill by doing almost nothing."[24]

Under the "agreement state" legislative framework of the Uranium Mill Tailings Radiation Control Act, the Nuclear Regulatory Commission left New Mexico to handle the dam failure until October 12, 1979, when it was notified that the state would permit the uranium mill to resume operation that week. The NRC then suspended United Nuclear's operating license until it could be determined that the embankment was stable.[25] After fewer than four months of downtime following the dam failure, the mill resumed operations on November 2, 1979. This further contaminated the groundwater and resulted in the mill site's placement on the EPA's National Priorities List in 1983.[6][13] United Nuclear made a $525,000 out-of-court settlement with the Navajo Nation a year after the spill.[26]

In terms of the amount of radioactivity released, the accident was larger in magnitude than the Three Mile Island accident of the same year.[2][5][6] The spill has been called "the largest radioactive accident in U.S. history," but the Nuclear Regulatory Commission has said that this is "an overstatement," and that "there have been a number of other events that have been more significant in terms of radiological impact. The event was more significant from an environmental perspective than from a human one."[1]


A diagrammed cross section of the breach from the report commissioned by the NRC. The "point" in the bedrock that UNC said acted as a fulcrum in the dam's breach is visible beneath the embankment.

The dam formed the southern wall of one of the mill's three holding ponds, which were used to evaporate tailings solution until the remaining solid waste could be buried.[27] During its operation from 1967 to 1982, the mill produced 3.5 million tons of tailings at the rate of 4,000 tons a day.[4][28][29] The 35-foot-high embankment was constructed on a deposit of collapsible clayey, silty sand a hundred feet deep.[16] United Nuclear used a new design, recommended by the Nuclear Regulatory Commission, that used earth rather than tailings themselves as building material.[20] The holding pond was not lined, in violation of standards in the Uranium Mill Tailings Radiation Control Act of 1978 that required that holding ponds be impermeable.[20] This lack of lining allowed tailings solution to seep into the ground, weakening the foundation of the dam and contaminating the groundwater.[16]

Horizontal and vertical cracks formed along the southern part of the embankment, allowing the acidic tailings solution to penetrate and weaken the embankment.[16] A sand beach was constructed to protect the face of the embankment from the tailings solution, but it was not properly maintained. Prior to the collapse, the level of the tailings solution in the holding pond had risen two feet higher than the dam's designed limit, and the sand beach no longer provided the dam protection.[16][30] The United States Army Corps of Engineers concluded in its report to Governor Bruce King of New Mexico that the principal cause of failure was differential settlement of the foundation beneath the dam wall,[31] and the report commissioned by the Nuclear Regulatory Commission corroborated this conclusion.[16] Critical variations in tailings pond operation practice from approved procedures contributed further to the dam failure.[20][31] United Nuclear's Chief Operating Officer, J. David Hann, blamed the failure of dam on the pointed shape of the bedrock beneath the embankment, which he said acted as a fulcrum and weakened the dam.[5]

Cracks were first noted in the dam wall by independent consultants in December 1977 and were sealed with bentonite and kerosene slurry in February 1978.[16] United Nuclear was notified of the cracking, but, aside from the initial seal, took little or no preventative action.[20] United Nuclear did not make regular inspections of the dam despite strong recommendations by independent consultants that it do so.[20] Further cracking was noted in October 1978. Neither the facility owner nor the State Engineer were formally notified of the episodes of cracking prior to the dam breach, though Arizona representative Morris K. Udall testified before Congress that at least three federal and state agencies had "ample opportunity" to predict that the dam's failure was likely.[31][32] At the same Congressional hearing, the United States Army Corps of Engineers testified that United Nuclear ignored warnings from the Corps that the dam was structurally unsound.[27]

Both New Mexico and Arizona were governed under the Uranium Mill Tailings Radiation Control Act as "agreement states," meaning that they, not the Nuclear Regulatory Commission, were responsible for ensuring compliance with NRC standards.[25] However, the states lacked the equipment and personnel to properly oversee tailings disposal sites statewide, and the ambiguity and drafting errors present in the act left them confused about how much regulatory power they had.[25][33]


A sign placed by the New Mexico Environmental Improvement Division discouraging use of the Puerco River.

Shortly after the breach, below the dam radioactivity levels of river water were 7000 times that of the allowable level of drinking water.[34] United Nuclear initially claimed that only one curie of radioactivity had been released in the spill, but that figure was later revised upward by the New Mexico Environmental Improvement Division.[35] In all, 46 curies (1.7 TBq) of radioactivity were released.[36]

The Puerco River in flood. After the tailings dam failure, 93 million gallons of acidic, radioactive tailings solution flowed into the Puerco River.[2]

Prior to the spill, local residents used the riverside for recreation and herb-gathering, and children often waded in the Puerco River.[6] Residents who waded in the river after the spill went to the hospital complaining of burning feet and were misdiagnosed with heat stroke.[18] Burns acquired by some of those who came into contact with the contaminated water developed serious infections and required amputations.[26] Herds of sheep and cattle died after drinking the contaminated water, and children played in pools of contaminated water.[27][37] The spill contaminated shallow aquifers near the river that residents drank and used to water livestock.[38] 1,700 people lost access to clean water after the spill.[27] United Nuclear Corporation distributed 600 gallon-jugs of clean water, but the affected area required more than 30,000 gallons of water daily.[2] The three community wells serving Church Rock had already been closed, one because of high radium levels and the other two for high levels of iron and bacteria.[39] The Indian Health Service advised the tribe to repair five shallow wells along the Puerco River and said that the wells "are not expected to show any contamination, if at all, for several years."[2] The Navajo Nation spent $100,000 on clean water,[40] and in 1981, the New Mexico and federal governments stopped providing water, which they had delivered by truck since the spill.[41]

An epidemiological study conducted by the NMEID in 1989 concluded that "the health risk to the public from eating exposed cattle is minimal, unless large amounts of this tissue, especially liver and kidney, are ingested."[42] An Indian Health Service study found significantly higher levels of radionuclides in Church Rock cattle compared to livestock from non-mining areas. The study's authors advised that contamination would not pose a risk as long as residents did not depend on livestock for food over long periods of time, but local Navajos did.[43] A few Navajo children were sent to Los Alamos to be checked for radiation exposure, but no long-term monitoring was undertaken, prompting a local writer to comment that the IHS spent more effort studying livestock than the people affected.[43] No ongoing epidemiological studies have been done at Church Rock.[6][44] Studies have shown since the 1950s that the Navajo have had significantly higher rates for some cancers than the national average, associated with contamination from the uranium mines and the exposure of workers to radiation.[45][46]


2009 map of remedial efforts at the United Nuclear Corporation site. The 1979 spill resulted from a breach of the South Cell dam.[4]

United Nuclear dispatched small crews with shovels and 55-gallon drums to begin cleanup, but expanded the workforce after complaints from local residents and pressure from the state.[30] The crews removed three inches of sediment from the river bed,[47] retrieving about 3,500 barrels (560 m3) of waste materials over the course of three months, but this amount was estimated as only 1% of the solid waste spilled.[6] Groundwater remained contaminated by the spilled tailings solution, and rain transported leftover pollutants downstream into Arizona.[18][30] New Mexico ordered United Nuclear to monitor pools left behind by the spill along the Puerco River, but United Nuclear only measured uranium levels, ignoring the presence of 230Th and 226Ra.[30] The pools contained high levels of sulfuric acid and remained for more than a month after the spill, despite cleanup efforts by the New Mexico Environmental Improvement Division.[35] The NMEID ordered United Nuclear to control tailings seepage from the mill in 1979, and the company implemented a limited seepage collective program in 1981.[28]

The Navajo Nation appealed to the governor to request that the president declare the site a federal disaster area, but he refused, reducing the aid available to local residents.[6] United Nuclear continued operation of the uranium mill until 1982, when it closed because of the declining uranium market.[48]

United Nuclear neutralized the acidity of the tailings with ammonia and lime from 1979 to 1982.[49] In 1983, the site was entered on the National Priorities List of the Environmental Protection Agency's Superfund investigations and cleanup efforts, as radionuclides and chemical constituents were found to be contaminating local groundwater.[13] The EPA conducted a remedial investigation from 1984 to 1987, and in the NRC approved United Nuclear's closure and reclamation plan in 1988.[49]

Removal of radium-contaminated soil in Church Rock in 2007.

In 1994 the EPA extended its efforts with a study of all known uranium mines on the Navajo Nation.[50][51]

The EPA and United Nuclear removed 175,500 cubic feet (4,970 m3) of radium-contaminated soil surrounding five buildings, some residential, in 2007.[29] The soil was moved to an off-site disposal facility.

In 2003 the Churchrock Chapter of the Navajo Nation began the Church Rock Uranium Monitoring Project to assess environmental impacts of abandoned uranium mines, and build capacity to conduct community-based research with policy implications.[11] Its May 2007 report found significant radiation remaining in the area, from both natural and mining sources.[11]

In 2008, the US Congress authorized a five-year plan for cleanup of contaminated uranium sites on the Navajo reservation.[52] The non-profit Groundswell Educational Films is hosting online videos of the cleanup effort.

See also[edit]


  1. ^ a b "Navajos mark 20th anniversary of Church Rock spill", The Daily Courier, Prescott, Arizona, July 18, 1999
  2. ^ a b c d e f g h i j k Pasternak, Judy (2010). Yellow Dirt: A Poisoned Land and a People Betrayed. Free Press. p. 149. ISBN 978-1416594826.
  3. ^ Lauri Wirt, "Radioactivity in the Environment: A Case Study of the Puerco and Little Colorado River Basins, Arizona and New Mexico"
  4. ^ a b c United Nuclear Corporation (McKinley County) (PDF), EPA, November 21, 2012
  5. ^ a b c d US Congress, House Committee on Interior and Insular Affairs, Subcommittee on Energy and the Environment. Mill Tailings Dam Break at Church Rock, New Mexico, 96th Cong, 1st Sess (October 22, 1979):19–24.
  6. ^ a b c d e f g h i j k l m Brugge, D.; DeLemos, J.L.; Bui, C. (2007), "The Sequoyah Corporation Fuels Release and the Church Rock Spill: Unpublicized Nuclear Releases in American Indian Communities", American Journal of Public Health, 97 (9): 1595–600, doi:10.2105/ajph.2006.103044, PMC 1963288, PMID 17666688
  7. ^ Quinones, Manuel (December 13, 2011), "As Cold War abuses linger, Navajo Nation faces new mining push", E&E News, retrieved December 28, 2012
  8. ^ Pasternak 2010, p. 150.
  9. ^ Dingmann, Tracy (July 16, 2009), "New attention to Church Rock uranium spill comes 30 years later", The New Mexico Independent
  10. ^ FSWarren, "The Bio-Weapon Projects", January 2019,
  11. ^ a b c Shuey, Chris; et al. (May 2007), Report of the Church Rock Uranium Monitoring Project 2003-2007, Churchrock Chapter, Navajo Nation, Southwest Research and Information Center and Navajo Education and Scholarship Foundation (PDF), Window Rock, Navajo Nation (Arizona), USA
  12. ^ "EPA Superfund Program: UNITED NUCLEAR CORP., CHURCH ROCK, NM". EPA. Retrieved 2016-04-26.
  13. ^ a b c Second Five-Year Review Report for the United Nuclear Corporation. Ground Water Operable Unit (PDF), EPA, September 2003, archived from the original (PDF) on 2011-05-31
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  35. ^ a b Robertson, Bill (October 4, 1979), "Pediatrician says spill underplayed" (PDF), New Mexico Daily Lobo
  36. ^ "Comparison of the Three Mile Island, Chernobyl, Sequoyah Fuels Corporation, and Church Rock Releases," American Journal of Public Health, 2007, 97(9) pp. 1595-1600.
  37. ^ Brown, Jovana J.; Lambert, Lori (2010), Blowing in the Wind: The Navajo Nation and Uranium, The Evergreen State College
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  39. ^ Pasternak 2010, p. 149-150.
  40. ^ Nelkin, Dorothy (1981), "Native Americans and Nuclear Power", Science, Technology & Human Values, 6 (2): 2–13, doi:10.1177/016224398100600201, JSTOR 689554
  41. ^ Chris Shuey, MPH "The Puerco River: Where Did the Water Go?", Southwest Research and Information Center, 1986
  42. ^ Lapham, SC, JB Millard, and JM Samet. "Health implications of radionuclide levels in cattle raised near U mining and milling facilities in Ambrosia Lake, New Mexico. Health Physics Journal, 1989, 56(3) pp. 327-40.
  43. ^ a b Pasternak 2010, p. 151.
  44. ^ Gunter, Linda (September 2009), "Remembering the Forgotten Nuclear Accident", Z Magazine, pp. 6–7
  45. ^ Chris Shuey, MPH Uranium Exposure and Public Health in New Mexico and the Navajo Nation: A Literature Summary Southwest Research and Information Center, 02.27.07, rev.10.14.08
  46. ^ Pinderhughes, Raquel (1996), "The Impact of Race on Environmental Quality: An Empirical and Theoretical Discussion", Sociological Perspectives, 39 (2): 231–48, doi:10.2307/1389310, JSTOR 1389310
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  48. ^ "UNC Resources Plans to Shut Last Uranium Mine Operation", The Washington Post, May 4, 1982
  49. ^ a b EPA Superfund Record of Decision: United Nuclear Corp., Church Rock, New Mexico: EPA, September 30, 1988
  50. ^ "Abandoned Uranium Mines On The Navajo Nation", EPA Region 9: Superfund, retrieved July 30, 2010
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  52. ^ Felicia Fonseca, "Navajo woman helps prompt uranium mine cleanup", Associated Press, carried in Houston Chronicle, 5 September 2011, accessed 5 October 2011

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