Underground

Plutonium Found in Nev. Groundwater
Associated Press, January 6, 1999

Traces of plutonium from a test blast in the Nevada desert migrated nearly a mile through groundwater, according to a study that prompted the government to recalculate slightly the risks that would be posed by an underground nuclear waste storage site. Scientists said the amount of radioactivity that can move this way is too small to endanger the public, and the U.S. Energy Department, in reassessing the risks of the government's proposed waste site beneath Nevada's Yucca Mountain, agreed. Until recently, it was commonly believed that significant amounts of plutonium would not move through groundwater because the element dissolves at a very low rate and attaches strongly to any rocks it touches.

But in a study published Wednesday in the journal Nature, researchers confirmed suspicions that plutonium can hitch a ride on colloids, or particles of debris suspended in water. Scientists from Lawrence Livermore National Laboratory in California and Los Alamos National Laboratory in New Mexico looked at a 30-year-old nuclear blast that reached below the water table on the Nevada Test Site, where the United States has conducted 828 underground nuclear tests between 1956 and 1992. The site is 70 miles northwest of Las Vegas. The scientists found minute amounts of plutonium measurable only by the most sensitive equipment in test wells nearly a mile away from the blast, and concluded that the plutonium had flowed downstream on colloids. "We have shown there is a new potential pathway that has been suggested before, but never definitely shown. The question is what the maximum amount is that you could move. We don't know that,'' said Annie Kersting, a Lawrence Livermore scientist.

The Energy Department wants to build a nuclear waste repository at Yucca Mountain, about 90 miles northeast of Las Vegas. The government has already spent $2.2 billion in 15 years of research in hopes of entombing 80,000 tons of used reactor fuel that will remain deadly 300,000 years. The department took the latest findings into account and concluded that the seepage wouldn't happen for 10,000 to 100,000 years, and even then, the escaped radiation would be less than the background amount. "They are not rates that would bust any kind of standards. We see no impact,'' said Abe Van Luik, senior technical advisor for performance assessment for the Energy Department.

Bruce Honeyman, a professor at the Colorado School of Mines, said the very nature of colloids their extremely small size and low concentrations assure that they would never move large amounts of radiation. "The radioactivity is so low that it probably is not of significance for adverse human health effects,'' he said. "Conceptually, you can think of colloids being like a conveyor belt. The belt is really not turning very quickly.'' The Energy Department's conclusions did not satisfy Bob Loux, executive director of the Nevada Agency for Nuclear Projects in the Nevada governor's office. He said he believes containers holding the waste will fail much more quickly than the government estimates and allow unknown quantities of contaminants to escape within 500 years.