X-ray Science Saves Taxpayers Billions in Radioactive Cleanup
Residents of the Rocky Flats watershed can rest easier knowing that decades of radioactive contamination have now been cleaned up. Taxpayers can also rest easier knowing that the largest Superfund cleanup in history has reached completion years ahead of schedule, at a savings of billions of dollarsa remarkable solution to a cold-war-era problem, thanks in part to modern x-ray science conducted at the Department of Energy's Stanford Linear Accelerator Center in collaboration with scientists from Los Alamos National Laboratories.
"This clearly demonstrates how science can play a very major role in improving the cost efficiency of site clean-up," said John Bargar, environmental scientist at the Stanford Synchrotron Radiation Laboratory (SSRL) and advocate of the Rocky Flats remediation project.
Coordinating the clean-up was complicated, but once scientists, decision-makers and stakeholders reached consensus on the best remediation approach to undertake, the project was completed in record time. X-ray studies at SSRL facilitated the project by positively identifying the contaminants involved, thereby enabling researchers to unambiguously eliminate unsuitable remediation options.
"Once the contractor, Kaiser-Hill, DOE, EPA, the state of Colorado, and the concerned citizens groups reached this common understanding of the technical issues, the groups were able to come together and reach a long-sought-after agreement on how to proceed with the cleanup," said David Clark, Los Alamos scientist and lead author of the article detailing clean-up efforts published in the September issue of Physics Today.
For nearly 40 years, the Rocky Flats Nuclear Weapons Plant, located just north of Denver, Co., served as a primary manufacturing facility for the U.S. nuclear weapons arsenal. Workers there machined weapons components using radioactive materials such as plutonium and uranium; toxic metals such as beryllium; and hazardous solvents, degreasers, and other chemicals.
Until the plant was abruptly closed in 1989 by the Department of Energy because of environmental concerns, the chief components made at Rocky Flats were plutonium pits—the primary trigger of a nuclear weapon. Nearly 40 years of nuclear weapons production left behind a legacy of contaminated facilities, soils and groundwater. Accordingly, in 1995, the site was designated as an EPA Superfund cleanup site.
The DOE estimated that cleaning up the entire site—then renamed the Rocky Flats Environmental Technology Site (RFETS)would take 70 years and would cost in excess of $37 billion. An independent contractor, the Kaiser-Hill Co., and the DOE undertook a massive effort to devise a subsequent plan, which brought the figure down to $7 billion over 10 years. But thanks to the aid of rigorous scientific detective work, that plan was completed in December of 2005decades ahead of the initial estimate, and at a cost of billions less.
Meeting the challenge of environmental remediation on this scale required a tightly focused scientific approach. The 1.6 square kilometer RFETS site comprised over 800 buildings surrounded by 24 square kilometers of open space, and at first, theories conflicted about how the contaminants were moving in the environment.
Evidence suggested a plume of fine particles had scattered into the soil downwind of the facility, but it wasn't until researchers confirmed the exact identity of the contaminants that they could say with certainty how those contaminants were being transported. Using X-ray Absorption Fine-structure (XAFS) spectroscopy at SLAC's Stanford Synchrotron Radiation Laboratory, scientists at Los Alamos concluded the RFETS contaminants were minute particles of plutonium that were not soluble in water, eliminating the danger of large-scale groundwater contamination. But, as Clark noted, "Just because the plutonium is insoluble doesn't mean that it's immobile."
With the results from SSRL, project managers adopted an "erosion model" to explain the observed dispersal. Remediation of the site subsequently focused on the top surface of sediments, where the majority of the contamination resided. Remediation crews took this information and placed large tents over certain sites to protect from wind and rain during cleanup efforts. To prevent further dispersal of the contamination, crews removed the top layer of soil, which was then properly disposed of as hazardous waste.
Today, RFETS stands as the most extensive environmental remediation project in the history of the Environment Protection Agency's Superfund program. This success is in part the result of x-ray science at SSRL.
"Using high-intensity x-rays from the synchrotron was the only direct way to determine the form of plutonium in the soil," said Los Alamos scientist Steve Conradson, who led the x-ray research conducted at SSRL. "It helped persuade all the stakeholdersincluding the public and its advocatesthat this was the right model for cleanup efforts."
Above image: The Rocky Flats site before and after cleanup. (Click on image for larger version.)