LAS VEGAS — Rainwater seeping into corroded 1970s-era barrels buried at a radioactive waste dump caused an explosion last month at the long-closed facility about 110 miles northwest of Las Vegas, Nevada’s top fire investigator said.
Radioactivity wasn’t detected after the Oct. 18 blast and fire, and no injuries were reported, Nevada Fire Marshal Peter Mulvihill said this week.
Several 55-gallon drums blown beyond the facility fence were returned to the crater and reburied, and the damaged area was filled with dirt and covered with a waterproof chemical membrane almost 1 inch thick, topped with more dirt, he said.
A previous statement from the Nye County sheriff said the site near Beatty had been covered with a heavy waterproof tarp.
“They’re going to look at a long-term solution and get advice how to proceed,” Mulvihill said Tuesday as he outlined findings he submitted for review by state, local, county and federal agencies handling the incident.
Mulvihill said the federal Energy Department and Nuclear Regulatory Commission, the Desert Research Institute of the University of Nevada, and the state Division of Environmental Protection are involved, along with the state Health Division. He said a final report could be made public in the coming days.
“The state of Nevada is responsible for this site,” Mulvihill said. “We’re accepting responsibility for being good stewards over the long haul.”
No escaped radiation was detected by first responders, investigators or repair crews during several visits to the site, he added.
The dump opened in 1962 as the nation’s first federally licensed low-level solid radioactive waste repository for waste including contaminated tools, protective clothing, machine parts, medical items and laboratory supplies. It closed in 1992. Records say the 40-acre property consists of 22 trenches up to 800 feet long and 50 feet deep.
The former site operator, US Ecology Inc., still operates a plant to treat, recycle and dispose of hazardous and nonhazardous waste on an adjacent 40 acres of state property.
US Ecology spokesman David Crumrine said records showed the material in the trench that exploded was buried between 1969 and 1973.
Mulvihill said state Radiation Control Program officials are combing through 89 boxes of records relating to the site that have been retrieved from state archives.
Two former Nevada governors have expressed doubt that accurate records exist.
Former Republican Gov. Robert List remembered ordering the Beatty low-level waste facility shut down in 1979 and launching a probe after a radioactive cargo fire on a truck parked on U.S. Highway 95 at the facility gate.
Three years earlier, employees were dismissed for stealing radioactive building materials and tools for home use. Operations resumed in the early 1980s after assurances that rules would be enforced.
Former U.S. Sen. Richard Bryan, a Democrat who was Nevada governor from 1983 to 1989, said that during hearings about the site no one ever said any of the materials buried at Beatty had a potential to catch fire.
Mulvihill said this week that unusually heavy rains that washed out roads and damaged historic structures in nearby Death Valley National Park puddled and drained through cracks in the trench cover mound. The water exploded when it contacted metallic sodium that had been buried in drums filled with oil.
The material was from a closed U.S. Bureau of Mines facility in Boulder City, east of Las Vegas, he said.
More than 1 inch of rain was recorded at Beatty during an Oct. 4-5 storm, and more than 1.25 inch fell Oct. 15-19, said Barry Pierce, National Weather Service hydrology program manager in Las Vegas. The rain caused intense flooding in the hard-baked desert where average rainfall for October is just 0.28 inches.
“The drums that the stuff was buried in 40 years ago corroded, the oil leaked out and water got in,” Mulvihill said. “That’s what caused the explosion.”
The fire marshal said tests confirmed that a fine white powder collected from around the blast crater was sodium hydroxide dust — one byproduct of the violent chemical reaction that also produces heat and hydrogen gas.