Two scientists at Los Alamos National Laboratory have published a feature article in the September issue of Physics Today about the scientific understanding that helped the U.S. government clean up waste at the Rocky Flats nuclear weapons production complex years ahead of schedule and save taxpayers billions of dollars. Los Alamos scientists David L. Clark and David R. Janecky together with Leonard J. Lane of L.J. Lane Consulting in Tucson, Arizona, wrote about the chemical and physical interactions of radioactive compounds, how these interact with the environment, and how best to manage them.
The authors detailed how good science clarified the scope of the most extensive cleanup in the history of Superfund legislation.
Rocky Flats was a U.S. Department of Energy site located about 16 miles northwest of downtown Denver. From 1952 to 1989, the Rocky Flats Plant made components for the nation's nuclear weapons arsenal using various radioactive and hazardous materials, including plutonium, uranium, and various cleaning solvents and degreasers. Closed in 1993, after nearly 40 years of nuclear weapons production work, the plant left a legacy of contaminated facilities, soils, and water.
At the beginning of the cleanup effort, modeling results didn't match the field measurements, which exasperated the remediation team and led to public mistrust. To make sense of the data-model disparity, a team of 10 experts, including 3 from Los Alamos, were invited to the site and provided technical expertise and advice on actinide behavior and mobility in the air, water, and soil. Clark and Janecky worked on the project for its entire 10-year duration.
The group provided independent advice on the use of state-of-the-art technologies to study the contamination levels and nature of compounds in the soil, building materials, and water. Such technologies as X-ray absorption near-edge structure, extended X-ray absorption fine-structure spectroscopy, and ultrafiltration led to a conclusion that the models being used were inappropriate.
Los Alamos researchers and Rocky Flats personnel used these techniques to determine the oxidation state of the site's waste plutonium. Plutonium in the fourth oxidation state tends to have a high affinity to bind with minerals and organic materials. The X-ray absorption studies demonstrated that the largest source of plutonium in the environment was a highly insoluble oxide form, indicating the largest threat to environmental transport would be the dispersal of particles by wind and surface water.
"Just because a compound is insoluble doesn't mean it's immobile -- getting everyone to that common understanding was a major milestone," says Clark.
"From the beginning, we committed to communicating thoroughly the scientific details of plutonium transport to all the stakeholder groups," explained Janecky.
Armed with this new knowledge, remediation experts could focus on the effort to control surface water and wind erosion processes that posed the greatest risk to human health.
"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," Clark said.
This understanding in turn allowed the site contractors to rapidly adopt a soil-erosion and sediment transport model rather than a model based on water transport.
The new understanding and integrated models provided the scientific basis for how to best negotiate a cleanup agreement and settle on an allowable standard of 50 picocuries per gram of soil. In 1996 the maximum allowable radionuclide action level was 651 picocuries per gram. A curie is a measure of the amount of radiation emitted by a radionuclide.
In 2002, armed with the improved understanding of the contamination and the behavior of plutonium found in the soils, the DOE, Colorado Department of Public Health, and EPA released a series of reports that formed the basis for the new maximum surface-soil action level.
Rocky Flats is now a wildlife refuge scheduled to partially open in 2007, and expected to be in full operation in 2012. The refuge will have hiking trails, interpretive signs, and limited hunting.
The entire article can be viewed at http://www.aip.org/pt/
More information about the Rocky Flats cleanup can be found in the latest issue of Actinide Research Quarterly at http://arq.lanl.gov
Photo available at http://www.lanl.gov/news/albums/Aerials/1995aerial.jpg
Photo available at http://www.lanl.gov/news/albums/Aerials/2005aerial.jpg
CAPTION: Aerial photos taken in 1995 (labeled as such) and photos taken in 2005 show the reconfigured Rocky Flats Environmental Site after buildings and pavement were removed 10 years later.
Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, The Babcock & Wilcox Company, and the Washington Division of URS for the Department of Energy's National Nuclear Security Administration.
Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.