Department of Water Resources
A daily compilation of significant news articles and comment
July 27, 2009
4. Water Quality –
RADIOACTIVE REMNANTS: Scientists monitoring groundwater from
Monitoring relies on plugging data into computer model
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RADIOACTIVE REMNANTS: Scientists monitoring groundwater from
Monitoring relies on plugging data into computer model
Radioactive groundwater laced with remnants of Cold War nuclear weapons tests is inching its way beyond the Nevada Test Site boundary where scientists expect they will 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 be found within the surrounding Air Force range in an area not accessible by the public.
The 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 Friday.
A recently completed well upstream of that one near a cavity of the powerful Benham nuclear test has produced field results 3,000 times in excess of the safe drinking water limit for tritium, said Bill Wilborn, director of the federal agency drilling campaign and groundwater characterization strategy.
"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," he said, discussing in a telephone interview a 687-page report on the effort to figure out where the tainted water is traveling.
The effort relies on plugging data from a network of wells into a sophisticated computer model.
A state official said that if the contamination appears to be heading toward a public water supply well, the Department of Energy will be required to provide water to impacted residences and communities in
"Obviously we're not close to that," said Tim Murphy, federal facilities bureau chief for the Nevada Division of Environmental Protection.
Nevertheless, he said, "We want to know what direction it is flowing and at what rate. Then when it gets to this point we're going to have to figure out options" for protecting the public.
"Unfortunately, today there is no technology to clean this up," 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.
DOE's Wilborn said preliminary indications are the contamination won't reach Beatty. Instead, perhaps hundreds or 1,000 years from now it will head between Beatty and
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 slug of 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 low-probability 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," said Wilborn, a geologist.
"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: 50 years on the low end, 1,000 on the high.
The tainted water is emanating from Pahute Mesa where devices for the Benham and Tybo nuclear tests were exploded in 1968 and 1975, respectively. 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
In a micro-second 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.
Said Murphy: "We're fortunate that the groundwater flow up there is very slow."
Based on a range of rates between initial wells, tritium in the water travels about nine feet per year. Scientists from Lawrence Livermore National Laboratory in
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 shots.
Under an agreement with the state, DOE is required to collect very high levels of radioactive-laced water from the wells in a lined sump or vessel.
Each well costs between $5 million and $7 million to drill including costs for road-building, constructing pads and sumps.
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. #
http://www.lvrj.com/news/51776577.html
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