Radioactive contamination from the Rocky Flats Plant in Colorado
The Rocky Flats Plant, a former United States nuclear weapons production facility located about northwest of Denver, caused radioactive (primarily plutonium, americium, and uranium) contamination within and outside its boundaries. The contamination primarily resulted from two major plutonium fires in 1957 and 1969 (plutonium is pyrophoric, and shavings can spontaneously combust) and from wind-blown plutonium that leaked from barrels of radioactive waste. Much lower concentrations of radioactive isotopes were released throughout the operational life of the plant from 1952 to 1992, from smaller accidents and from normal operational releases of plutonium particles too small to be filtered. Prevailing winds from the plant carried airborne contamination south and east, into populated areas northwest of Denver.
The contamination of the Denver area by plutonium from the fires and other sources was not publicly reported until the 1970s. According to a 1972 study coauthored by Edward Martell, "In the more densely populated areas of Denver, the Pu contamination level in surface soils is several times fallout", and the plutonium contamination "just east of the Rocky Flats plant ranges up to hundreds of times that from nuclear tests." As noted by Carl Johnson in Ambio, "Exposures of a large population in the Denver area to plutonium and other radionuclides in the exhaust plumes from the plant date back to 1953."
Weapons production at the plant was halted after a combined FBI and EPA raid in 1989 and years of protests. The plant has since been shut down, with its buildings demolished and completely removed from the site. The Rocky Flats Plant was declared a Superfund site in 1989 and began its transformation to a cleanup site in February 1992. Removal of the plant and surface contamination was largely completed in the late 1990s and early 2000s. Nearly all underground contamination was left in place, and measurable radioactive environmental contamination in and around Rocky Flats will probably persist for thousands of years. The land formerly occupied by the plant is now the Rocky Flats National Wildlife Refuge. Plans to make this refuge accessible for recreation have been repeatedly delayed due to lack of funding and protested by citizen organizations.
The Department of Energy continues to fund monitoring of the site, but private groups and researchers remain concerned about the extent and long-term public health consequences of the contamination. Estimates of the public health risk caused by the contamination vary significantly, with accusations that the United States government is being too secretive and that citizen activists are being alarmist.
Background.
The Rocky Flats Plant was south of Boulder, Colorado, and northwest of Denver. Originally under the Dow Chemical Company's management, it was transferred to Rockwell in 1975. It initially had an area of ; a buffer zone was added in 1972.
Construction of the first buildings began on July 10, 1951. Production of parts for nuclear weapons began in 1953. At the time, the precise nature of the work at Rocky Flats was a closely guarded secret. The plant produced fission cores for nuclear weapons, used to "ignite" fusion and fissionable fuel. Fission cores resemble miniaturized versions of the Fat Man nuclear bomb detonated above Nagasaki. They are often called "triggers" in official and news documents to obfuscate their function. For much of its operational lifetime, Rocky Flats was the sole mass-producer of plutonium components for America's nuclear stockpile.
Management of the site passed to EG&amp;G in 1990, which did not reapply for the contract in 1994. Management of the site passed to the Kaiser-Hill Company on July 1, 1995. The Department of Energy now manages the central portion of the site, where the production buildings once were, while the Fish and Wildlife Service has taken over management of the Peripheral Outer Unit.
Sources of contamination.
Most of the radioactive contamination from Rocky Flats came from three sources: a catastrophic fire in 1957, leaking barrels in an outdoor storage area in 1964–1968, and another, less severe fire in 1969. Plutonium, used to construct the weapons' fissile components, can spontaneously combust at room temperature in air. Additional sources of actinide contamination include inadequate pondcrete vitrification attempts and routine releases during the plant's operation.
1957 fire.
On the evening of September 11, 1957, plutonium shavings in a glove box in building 771, the Plutonium Recovery and Fabrication Facility, spontaneously ignited (plutonium is pyrophoric). The fire spread to the flammable glove box materials, including plexiglas windows and rubber gloves. It rapidly spread through the interconnected glove boxes and ignited a large bank of high-efficiency particulate air (HEPA) filters in a plenum downstream. Within minutes the first filters had burned out, allowing plutonium particles to escape from the building exhaust stacks. The building exhaust fans stopped operating due to fire damage at 10:40 PM, which ended most of the plutonium release. Firefighters initially used carbon dioxide fire extinguishers because water can act as a moderator and cause plutonium to go critical. They resorted to water hoses when the dry fire extinguishers proved ineffective.
The 1957 fire released 11–36 Ci () of plutonium, much of which contaminated off-site areas as microscopic particles entrained in smoke from the fire. Isopleth diagrams from studies show parts of Denver in the area where surface sampling detected plutonium. That the fire had resulted in significant plutonium contamination of surrounding populated areas remained secret. News reports at the time reported, per the Atomic Energy Commission's briefing, that there was slight risk of light contamination and that no firefighters had been contaminated. No abnormal radioactivity was reported by the Colorado Public Health Service.
Pad 903 leakage.
Plutonium milling operations produced large quantities of toxic cutting fluid contaminated with particles of plutonium and uranium. Thousands of 55-gallon drums of the waste were stored outside in an unprotected earthen area called the 903 pad storage area, where they corroded and leaked radionuclides over years into the soil and water. An estimated of plutonium-contaminated oil leached into the soil between 1964 and 1967. Portions of this waste, mixed with dust that composed Pad 903, became airborne in the heavy winds of the Front Range and contaminated offsite areas to the south and east.
Leaking storage barrels at Pad 903 released 1.4–15 Ci () of plutonium as airborne dust during the storage and subsequent attempts at remediation. Much more remains interred under the Pad 903 area, which has been paved over with asphalt.
1969 fire.
Another major fire occurred on May 11, 1969, in building 776/777 (the Plutonium Processing Facility), again from spontaneous combustion of plutonium shavings in a glove box. Firefighters again resorted to water after dry extinguishers proved ineffective. Despite recommendations after the 1957 fire, suppression systems were not built into the glove boxes.
While the fire bore marked similarities to the 1957 fire, the level of contamination was less severe because the HEPA filters in the exhaust system did not burn through (after the 1957 fire, the filter material was changed from cellulose to nonflammable fiberglass). Had the filters failed or the roof (which sustained heavy fire damage) been breached, the release could have been more severe than the 1957 fire. About of plutonium was in the storage area where the fire occurred, and about total plutonium was in building 776/777.
The 1969 fire released 13–62 mCi () of plutonium, about ;templatestyles src="Fraction/styles.css" / ;1⁄1000 as much as was released in the 1957 fire. But the 1969 fire led local health officials to perform independent tests of the area surrounding Rocky Flats to determine the extent of the contamination. This resulted in the first releases of information to the public that populated areas southeast of Rocky Flats had been contaminated.
Other sources.
Rockwell workers mixed hazardous and other wastes with concrete to create one-ton solid blocks called pondcrete. These were stored in the open under tarps on asphalt pads. The pondcrete turned out to be weak storage, an outcome Rockwell's engineers had predicted. Relatively unprotected from the elements, the blocks began to leak and sag. Nitrates, cadmium and low-level radioactive waste began to leach into the ground and run downhill toward Walnut Creek and Woman Creek.
Most of the plutonium from Rocky Flats was oxidized plutonium, which does not readily dissolve in water. A large portion of the plutonium released into the creeks sank to the bottom and is now found in the streambeds of Walnut and Woman Creeks and on the bottom of local public reservoirs just outside Rocky Flats: Great Western Reservoir (no longer used for city of Broomfield drinking water consumption as of 1997 but still used for irrigation) and Standley Lake, a drinking water supply for the cities of Westminster, Thornton, Northglenn and some residents of Federal Heights. As one of several forms of remediation and once the extent of the lapses at Rocky Flats became public knowledge, several streams formed by drainage through the contaminated areas of the Rocky Flats Plant were diverted so that they would no longer flow directly into some of the local reservoirs, such as Mower Reservoir and Standley Lake. Also, a surface water control system was built to allow runoff from contaminated creeks to collect in holding ponds and thus reduce or prevent direct runoff into Standley Lake. Proposals to remove or breach some of these dams to reduce the cost of maintenance have been protested by the cities downstream.
Reporting of contamination.
No radioactivity warning, advisement or remediation was provided to the public in the 1957 fire, the worse of the two. At the time, AEC officials told the "Denver Post" that the fire "resulted in no spread of radioactive contamination of any consequence". The public was not informed of substantial contamination from the 1957 fire until after the highly visible 1969 fire, when civilian monitoring teams confronted government officials with measurements made outside the plant of radioactive contamination suspected to be from the 1969 fire, which consumed hundreds of pounds of plutonium (850 kg).
The 1969 fire raised public awareness of potential hazards the plant posed and led to years of increasing citizen protests and demands for plant closure. Releases from previous years had not been reported publicly before the fire; airborne-become-groundborne radioactive contamination extending well beyond the Rocky Flats plant was not publicly reported until the 1970s.
Most contamination was centralized in the 385 acres where the 800 industrial buildings were.
In 2002, the U.S. Fish and Wildlife Service surveyed tissues harvested from deer that lived at Rocky Flats for plutonium and other actinides. Isotopes of plutonium, americium, and uranium were detected, with the highest measured activity being 0.0125 pCi/g of uranium-233, 234. The study found that the increased cancer risk to an individual who ate of Rocky Flats deer meat per year for 70 years was at most 1 in 210,000. This is near the conservative end of the EPA's acceptable risk range.
In August 2019, the Colorado Department of Public Health and Environment observed mixed results during testing of the Rocky Flats area for soil contamination. The testing, completed by the Jefferson Parkway Public Highway Authority in preparation for road construction, observed one soil sample with a plutonium level of 264 picocuries per gram. For reference, the Rocky Flats remediation standard is 50 picocuries per gram. A second sample registered just 1.5 picocuries of plutonium per gram. As of October 2019, testing of the area was ongoing. In February 2020, the parkway construction project was shut down and local civic authorities withdrew their support when plutonium samples with concentrations five times higher than the remediation standard were found.
Contamination and health studies.
Plutonium-239 and 240 emit ionizing radiation in the form of alpha particles. Inhalation is the primary pathway by which plutonium enters the body, though plutonium can also enter the body through a wound. Once inhaled, plutonium can increases the risk of lung cancer, liver cancer, bone cancer, and leukemia. Once absorbed into the body, the biological half-life of plutonium is about 200 years. This means that only a small fraction of the plutonium will be excreted during the average person's lifetime, and the rest will remain in the body where it can do harm.
Following the public 1969 fire, surveys were taken of the land outside the boundaries of Rocky Flats to quantify the amount of plutonium contamination. Researchers noted that plutonium contamination from the plant was present, but did not match the wind conditions of the 1969 fire. The 1957 fire and leaking barrels on Pad 903 have since been confirmed to be the main sources of plutonium contamination. Authors Krey