Five years from now, scientists may be able to better determine how, when and why plutonium moves in soil and ground water.

The way to predict how plutonium is transported in ground water away from a site is by looking at the dominant geochemical processes that control plutonium's (Pu) behavior in the subsurface at environmental levels. But that isn't always so easy.

A $6 million five-year proposal funded by the Department of Energy's (DOE) Office of Science, Biological and Environmental Research (BER), will allow about a dozen Lawrence Livermore National Lab (LLNL) scientists to study Pu transport at concentration levels at the picomolar to attomolar scale (equivalent to dissolving one grain of salt in 100 Olympic-size swimming pools).

Plutonium can move on small particulates, called colloids, which often are found in ground water, but the conditions that control whether it migrates or remains immobile are not well understood.

That's where the lab's team comes in. Annie Kersting, director of the Lab's Glenn T. Seaborg Institute and manager of the study, says that previous experiments of plutonium movement in the subsurface were performed at Pu concentrations orders of magnitude higher than those observed in the field. Now they will do experiments at much lower, environmental conditions.

Ultimately, the research will help in the development of conceptual models for Pu transport across the Department of Energy complex. The model will provide DOE with the scientific basis to support decisions for the remediation and long-term stewardship of legacy sites, Kersting notes.

"We can provide DOE an understanding of when and how Pu is transported in ground water," she says. "What process did it go through to get there, could it affect people downstream of DOE sites, and how can we predict and monitor Pu contamination?"

Mavrik Zavarin, the lead scientist, explains that it's likely the team will discover that Pu behavior is very much dependent on concentration. "At very low concentrations, Pu will interact with ground water, minerals and microbes in ways we could not have predicted based on past experiments," he says. "Our team at LLNL has a unique opportunity to study Pu chemistry under environmentally relevant conditions."

Laboratory results will be compared to field samples taken from three DOE sites: Nevada Test Site, Rocky Flats and the Hanford Site. Pu-containing colloids will be collected and characterized in terms of their inorganic surfaces, associated organic compounds/coatings and possible microbial associations.