13 March 2001
Learning Uranium Containment From Nature
by Kate Melville
Three decades ago, possibly one of the richest uranium deposits in the US was discovered at Coles Hill in rural South-central Virginia. Although the deposit was considered for mining, it was never developed. However, this site may yield knowledge of great value as a natural laboratory for radioactive waste containment.
"The uranium has just been sitting there for hundreds of thousands of years, " says A. K. Sinha, professor of geological sciences at Virginia Tech. "Sitting there" are the operative words. "There is a water table about 11 meters (36 feet) down, and the uranium-rich bedrock about 20 meters (66 feet) down. The uranium should have migrated to the next county, but it hasn't."
"You would expect ground water in this type of natural system to have carried the uranium away from the site into the surrounding environment, but we don't see that," says Virginia Tech Ph.D. student Jim Jerden, of Atlanta, Ga. "We think we can learn something from this site that can be applied to existing contaminated sites and nuclear waste repositories."
Sinha explains, "Uranium is toxic, particularly when it is concentrated, such as in nuclear fuel, weapons, and radioactive wastes.
In nature, there are deposits that are extremely concentrated and they should be of great concern, as uranium may be transported in solution through ground water activity. But, in nature, things have a way of reaching a 'steady state'. The Coles Hill deposit, for instance, shows no measurable evidence of leakage into the surrounding soils and rocks. This 'natural analog' provides a scientific window where we can study what prevents uranium from contaminating its surroundings."
As geologists, Sinha and Jerden are looking at the natural system that contains the Coles Hill uranium deposit as a unique geologic analog for uranium-contaminated sites and nuclear waste repositories. "Nature may present a model for the scientifically sound management of nuclear wastes and contaminated sites," says Jerden.
Jerden will present some of his research from Coles Hill at the 36th annual meeting of the Northeastern Section of the Geological Society of America (GSA) in Burlington, Vermont, March 12-14. "I will talk about the interaction of soil, rock, and ground waters, and the details of the minerals that inhibit uranium from being transported into the surrounding environment. Specifically, we have discovered that the abundance of phosphorous and its interaction with uranium is likely the cause for the lack of migration," he says.
Later this month, Sinha, Jerden, and Lucian W. Zelazny, professor of soil sciences at Virginia Tech, will meet with scientists from the University of Georgia's Savannah River Ecology Laboratory (SREL) and the University of South Carolina medical program to discuss a research partnership for using advanced technologies for a better understanding of the behavior of uranium in soils.
"SREL scientists have been experimenting with phosphorous and uranium in the laboratory. The goal of these experiments was to develop new cost effective technologies that can be applied for remediation of uranium contaminated sites, so they were very interested when we told them we were researching a natural system in which uranium and phosphorus are combining to naturally limit uranium transport," explains Jerden.
It is not just the richness and the self-containment of the deposit located only two hours away from Virginia Tech's Blacksburg campus (south east of Chatham, Virginia, near the little town of Gretna) that makes it such a unique resource for researchers. "The corporation that discovered the site did extremely good exploration of this deposit," explains Sinha. "They drilled approximately 70,000 feet of solid rock (70 1,000-foot cores). They created an enormous database. It would cost the government tens of millions of dollars to do that today, but this cost was borne by industry." When the mining activities were abandoned the corporation donated their information to Virginia Tech, and gave the cores for storage to the Virginia Museum of Natural History.
"We have an infrastructure database already generated at no cost to the taxpayer," says Sinha. "Virginia Tech has augmented this database through shallow drilling supported by the Virginia Division of Mineral Resources and is using the data and the samples to prove the site is a world class scientific target for research.
"We are asking basic questions," he says. "What are the natural processes that inhibit migration of uranium? If we can understand that, then our colleagues in engineering and other sciences can apply that knowledge to develop better strategies for cleaning up and managing contaminated sites and nuclear waste repositories.
"We are working in partnership with other institutions that wish to characterize this site so that all the people interested in the environment can use these resources to understand the transport of uranium," Sinha concludes.