Scientists have found the first radioactive tritium from nuclear weapons tests in a monitoring outside the Nevada Test Site's boundary.
The levels, reported Tuesday by the National Nuclear Security Administration, were within safe drinking water guidelines. The relatively short-lived isotope had migrated two miles through groundwater layers in 35 years to reach the boundary.
Sample results were verified by an independent laboratory and reported to state environmental officials, NNSA officials said in a news release.
Scientists believe it will take and estimated 240 years for the tritium-laced water to travel another 14 miles to the nearest public water source. By that time it will have decayed to non-detectable limits, said Darwin Morgan, a spokesman for the NNSA's Nevada Site Office.
"The big thing to us is it shows the models are accurate and gives us higher confidence in our ability to understand what is going on with deep groundwater," he said Wednesday.
Scientists said in July they probably would find tritium after completion of Well EC-11 near the northwest edge of the test site. Underground tests Benham and Tybo were detonated in Pahute Mesa, two miles from that location in 1968 and 1975, respectively.
Computer models of tritium migration predicted groundwater laced with it would travel beyond the test site within 50 years of the first detonation in Pahute Mesa, which occurred in 1966.
The NNSA, a branch of the Department of Energy, plans to drill six additional wells in or near Pahute Mesa in the next few years. The average depth of those wells will be 3,500 feet. They will cost about $5 million apiece.
Although tritium is an indicator of the radioactive remnants from powerful nuclear explosions, questions remain about how fast longer-lived isotopes such as plutonium are traveling. It's likely they are migrating at a much slower pace, Morgan said.
Nevertheless, he said, "We still have to understand if those longer-lived products are moving and, if so, how far are they moving."
In July, the director of the federal agency drilling campaign, Bill Wilborn, said the contamination probably won't reach Beatty, 120 miles northwest of Las Vegas. 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. The Obama administration has declared the site not an option for building a repository.
Contact reporter Keith Rogers at firstname.lastname@example.org or 702-383-0308.