Scientists checking Nevada Test Site groundwater

08/01/2009

By KEITH ROGERS Las Vegas Review-Journal
San Jose Mercury-News

LAS VEGAS - Radioactive groundwater laced with the remnants of Cold War nuclear weapons testing is inching its way beyond the Nevada Test Site boundary, where scientists expect to soon find it for the first time.

The concentration of tritium is much higher than safe drinking water guidelines, but Department of Energy officials note it will still be contained within the surrounding Nellis Air Force Base test and training range, in an area not accessible by the public.

A pad and sump, or pit, for what's labeled Well EC-11 are being completed, with the first samples to be collected as drilling proceeds in the next three months, the federal scientist in charge of the project said.

"Under our strategy we don't do any remediation. The only thing we can do at this point is adopt a long-term monitoring plan," said Bill Wilborn, director of the drilling and monitoring project.

Water from a recently completed upstream well, near a cavity of the powerful Benham nuclear test of 1968, has found tritium levels 3,000 times above the safe drinking water limit, Wilborn said.

The effort outlined in a 687-page report is to determine where the tainted water is traveling. It relies on plugging data from a network of wells in Nye County into a sophisticated computer model.

A state official said that if the contamination appears to be heading toward a public water well, the Department of Energy will be required to provide water to affected residences and communities.

"Obviously we're not close to that," said Tim Murphy, federal facilities bureau chief for the Nevada Division of Environmental Protection.

Murphy said there is no current technology to clean up the contamination. But authorities want to know where and how fast it is flowing to protect the public.

"Then when it gets to this point we're going to have to figure out options," Murphy said.

"What do we do if the model shows this is streaming downhill? We're going to have to direct the Department of Energy to provide another (water) source," he said.

Wilborn, the Energy Department geologist, said preliminary indications are the contamination won't reach Beatty, a Nye County community of about 1,000 residents some 115 miles from Las Vegas and midway between the test site and Death Valley National Park.

Instead, perhaps hundreds or 1,000 years from now it will head between Beatty and Yucca Mountain, where the Department of Energy had planned to dispose of the nation's spent nuclear fuel until the Obama administration declared the site not an option for building a repository.

Drill rigs in a remote area of Pahute Mesa more than 100 miles northwest of Las Vegas have been working to confirm what computer modeling predicts about the tritium contamination moving slowly through water layers about 1,500 feet beneath the surface.

If or when it will reach Coffer's Ranch windmill, the nearest long-term public monitoring well 15 miles southwest, is a guess.

"It's a complicated answer. We have mostly conceptual models of when contamination will be off the test site and how far down-gradient it will go," Wilborn said.

"It's going to be more probabilistic. There will be more uncertainties and unknowns down-gradient," he said.

The time frame for reaching Coffer's Windmill, he said, is 50 years on the low end and 1,000 on the high end.

The tainted water is emanating from Pahute Mesa where devices for the Benham and Tybo nuclear tests were exploded. Benham, the more powerful of the two, produced a yield equivalent to detonating 1.15 megatons of TNT, much larger than the yields from the atomic bombs dropped on Hiroshima and Nagasaki during World War II. Tybo was conducted in 1975 at less than 1000 kilotons.

In a microsecond burst, scientists believe contamination from the Benham detonation, including trace amounts of plutonium and isotopes that take much longer to decay to safe levels than tritium, were injected through bedrock and into groundwater layers.

Tritium is used to enhance the power of nuclear bombs. Some is created when special materials explode in the chain reaction. It has a half-life of more than 12 years, meaning that's the time it takes for half of its radioactive atoms to decay.

Other isotopes with much longer half-lives such as those from chlorine, iodine and technetium have dissolved and are moving along with the water. In addition, traces of plutonium have been found.

"We're fortunate that the groundwater flow up there is very slow," Murphy said.

Based on a range of rates between initial wells, tritium travels in the water about nine feet per year. Scientists from Lawrence Livermore National Laboratory in California and the Los Alamos National Laboratory in New Mexico will analyze sample results next year to link the contaminants to particular nuclear tests.

In all, 82 underground nuclear tests were conducted in Pahute Mesa out of at least 828 throughout the Nevada Test Site from 1951 to 1992, plus 100 above ground tests.

Under an agreement with the state, the Energy Department is required to collect very high levels of radioactive-laced water from the wells in a lined sump or vessel.

Each well costs $5 million to $7 million, including costs for road-building, constructing pads, sumps and drilling.

The project will cost $33 million this year and $35 million next year.

In all, nine wells will be drilled over the next three years using $12.1 million in government stimulus money to augment part of the effort, Wilborn said.

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