Early in the morning of July 16, 1979, there was a breach in the earthen retaining dam of a tailings pond at the United Nuclear Corporation's (UNC's) Church Rock uranium mill. The acidified liquid and tailings slurry spilled through the damaged portion of the retaining wall into an arroyo that is a tributary to the Rio Puerco river system. An estimated 94 million gallons of acidic waste water were released to the Pipeline Arroyo, and hence to the North Fork of the Puerco, when an earthen tailings dam located at the United Nuclear Corporation Church Rock Uranium Mill failed on the morning of July 16, 1979. The mill process fluids, which had a pH of less than 2 and a gross alpha particle activity of 128,000 picocuries per liter (pCi/1), traveled downstream into Arizona before dissipating into the stream bed near Chambers. The incident, which became known as the "Church Rock Tailings Spill," remains the largest release (by volume) of low-level radioactive waste in U.S. history.

The Rio Puerco runs through Gallup, New Mexico, and eventually crosses the New Mexico-Arizona border On its way to Gallup, the Rio Puerco and its tributaries pass through land with a checkerboard pattern of ownership, with portions owned or leased by the Navajos, individuals, the Bureau of Land Management, and the State.

History of contamination from the mill

The UNC uranium mill was granted a radioactive materials license by the State of New Mexico in May 1977, and operated from June 1977 to May 1982. The mill, designed to process 4,000 tons of ore per day, extracted uranium using conventional crushing, grinding, and acid-leach solvent extraction methods. Uranium ore processed at the Site came from the Northeast Church Rock and the Old Church Rock mines. The average ore grade processed was approximately 0.12 percent uranium oxide. The milling of uranium ore produced an acidic slurry of ground waste rock and fluid (tailings) that was pumped to the tailings disposal area. Uranium milling and tailings disposal were conducted and an estimated 3.5 million tons of tailings were disposed in the tailings impoundments.

Specific technical findings

A study conducted by the Navajo Nation and the Southwest Research and Information Center, Albuquerque, New Mexico, from 2003 to 2007 generated the folowing findings:

• Water quality in 17 unregulated water sources — drilled wells, dug wells and developed springs that are not regularly tested or treated to comply with federal and tribal safe drinking water standards — ranged from good to poor. None of the 17 sources tested were of sufficient quality to warrant recommendations for human drinking water use. Half of the water sources tested were not recommended for domestic uses, such as cooking, bathing and irrigating gardens, and most of the other half were recommended only with caution. Most of the water sources were suitable for livestock watering.
• Two wells were shut down and abandoned because of unsafe water quality during the course of the Project, and a “no human use” advisory was placed on another water source because of uranium levels exceeding the federal drinking water standard by more than two times.
• Only 1 of the 17 wells exceeded the federal drinking water standard for uranium, a rate (6%) that is substantially lower than recent water quality surveys conducted by federal agencies in the western part of the Navajo Nation that found that 14% to 20% of water sources tested exceeded the uranium standard of 30 micrograms per liter. Mine-water discharges to the Puerco River — the principal intermittent stream in the study area — in the 1960s, ’70s and ’80s were not safe for human or animal consumption, even though observational and anecdotal evidence indicated that residents often used mine water in the river and its tributaries for domestic uses and livestock watering was routine for least 18 years. The long-term effects of those discharges on surface water and shallow groundwater quality remain uncertain.
• In the northern half of the study area where past uranium mining was concentrated, gamma radiation rates were significantly elevated over background along public highways and roads, on Navajo grazing lands and in certain residential areas in close proximity to three abandoned uranium mines and a closed uranium mill and tailings disposal facility that is a federal Superfund site.
• Surface gamma radiation rates and uranium concentrations in soils near residences in the Red Water Pond Road area of Study Area A-1 were many times higher than background, indicating a potential public health emergency for residents of the area. CRUMP’s assessment in this area was confirmed in November 2006 by soil sampling conducted by USEPA and contractors to the company that operated the Northeast Church Rock Mine in the area from 1968 through 1982. As a result, radium-contaminated soils are being excavated from around at least five homes in the area as part of a USEPA-led “time-critical removal action” that eventually will lead to reclamation of the mine site and its surroundings.

Superfund designation

The talings operation is associated with the Northeast Church Rock Mine (NECR), a former uranium mine that was operated by United Nuclear Corporation (UNC) from 1967 to 1982. Most of the 125-acre mine permit area is held in trust for the Navajo Nation by the United States Government and is immediately adjacent to the Navajo Reservation. Approximately 40 acres are patented mining claim land owned by UNC. There is a small community of residents that live immediately next to the mine site on the reservation, downstream and down-wind of the waste piles. The residents graze sheep, cattle and horses, and collect herbs around the area.

The mining activities have resulted in a legacy of waste piles, sediment settling ponds abandoned building pads and mine equipment debris. Pollutants include acidic mill tailings, total dissolved solids, sulfate, thorium, radium, aluminum,
ammonia, and iron. In 1983 the site was desinged as a Superfund site bythe U.S. Environmental Protection Agency (Superfund is the name given to the federal environmental program established to address abandoned hazardous waste sites). When the Church Rock Mine was closed, several basic activities took place to protect future land users and neighbors. The majority of the buildings and equipment were cleared from the area. Some of the mine waste piles were returned to the shafts. Remaining waste piles were contoured to reduce movement of the material. The ponds were drained and a fence was installed around the mine site and associated areas.

While the mine was in operation the Nuclear Regulatory Commission (NRC) and the New Mexico Mining and Minerals Division regulated the site.

EPA has detected widespread radium contamination in 14 areas on and off-site, including the Sandfill areas, the ponds, the waste piles, the Non Economic Storage Area, the Boneyard. Beyond the permit boundary, Vent Holes #3 and 8, a parking area adjacent to the NECR 1 waste pile, a former trailer park, the unnamed arroyo and four residential yards also present elevated radium and uranium levels.

At present, there is an elevated health risk for people who frequent the site from inhaling radium contaminated dust particles, associated radon gas or utilizing contaminated rainwater and runoff that has pooled in the ponds. There is an elevated risk associated with livestock that may graze and water on the site. Elevated concentrations (activity) of Radium-226 have been detected throughout the 125-acre mine permit boundary and contiguous surface areas. Different radionuclides emit gamma rays of varying strength, but gamma rays can travel long distances and penetrate entirely through the body. Exposure to high levels of Radium-226 over a long period of time may result in harmful effects including anemia, cataracts, fractured teeth, cancer (especially bone cancer), and death. Exposure to high levels of uranium can cause kidney disease. It is not known to cause cancer, but can decay into other radioactive materials that may.

Remediation

The cleanup includes the following remedies:

• Containment and removal of contaminated ground water.
• Evaporation of ground water removed from aquifers using evaporation ponds supplemented with mist or spray systems to enhance the rate of evaporation.
• Implementation of a monitoring program to detect any increases in the areal extent, or concentration of ground water contamination at, and outside of, the boundary of the tailings disposal area.
• Implementation of a performance monitoring and evaluation program to determine water levels and contaminant reductions in each aquifer, and the extent and duration of pumping actually required outside the tailings disposal area.

Sources

• Shuey, Chris, Contaminant Loading on the Puerco River: A Historical Overview, Southwest Research and Information Center, Albuquerque, New Mexico, October 14, 1992.

• Shuey, Chris, Report of the Church Rock Uranium Mining Project, Southwest Research and Information Center, Albuquerque, New Mexico, May 2007.
  
• http://www.sric.org/uranium/CRUMPReportSummary.pdf.
• Ruttenber, A. James, Jr. ; Kreiss, Kathleen. 1981. Chapter 115 - Radiation Exposure Assessment (II) , in Radiation Hazards In Mining: Control, Measurement, and Medical Aspects.
• United States Environmental Protection Agency, Region 6, Second Five-Year Review Report for the United Nuclear Corporation, Ground Water Operable Unit
  Church Rock McKinley County, New Mexico, September 2003.
• United States Environmental Protection Agency, Region 6, Superfund Site: Northeast Church Rock Mine, Accessed 3 September 2008.