It could be some time before officials know what caused a fire at a low-level radioactive waste dump in Nye County that shut down a 140-mile stretch of Nevada's main north-south highway for almost 24 hours.
U.S. Highway 95 reopened to traffic Monday evening after tests conducted from the air and on the ground showed no signs of radioactive contamination from the blaze that broke out Sunday afternoon at the US Ecology waste site about 110 miles northwest of Las Vegas.
In a conference call Monday night, State Fire Marshal Chief Peter Mulvihill said investigators would be taking a close and methodical look at the site "once it is safe to go down there."
He said it's still too early to know what might have sparked the fire, which was reported about 1 p.m. Sunday in one of the site's low-level radioactive waste disposal trenches and was allowed to burn itself out over the course of about 12 hours.
Concerns about possible contamination from the fire prompted authorities to cancel school in the nearest town of Beatty and close U.S. 95 from state Route 160, about 70 miles northwest of Las Vegas, to the Nye County seat of Tonopah, 210 miles northwest of Las Vegas, about 7 p.m. Sunday.
US Ecology officials said they created "an exclusion zone around the facility" at the request of state regulators, but storms in the area Sunday night delayed efforts to survey the site from the air.
Federal aircraft that can detect radioactive particles conducted flights Monday morning, followed by a detection team on the ground that started in Beatty, 10 miles to the north, and worked its way to the waste facility.
Once it was determined that the fire was out and the surrounding area was safe from radioactive contamination, the highway was reopened about 5:30 p.m. Monday, releasing a flood of vehicles that had been trapped overnight in Beatty.
Mike Harmon, chief of the local volunteer fire department, said all of the motel rooms in town were filled with stranded travelers, and a line of vehicles a half-mile long was waiting at the road block for the highway to reopen.
He guessed there were 30 to 40 tractor-trailers parked along the road and packed into various parking lots in the town of about 1,000 people.
"It's pretty full," Harmon said.
Before the fire, flooding on roads throughout the area had already prompted the Nye County School District to cancel classes Monday in Amargosa Valley, about 20 miles south of US Ecology. The two public schools in Beatty were closed Monday as a precautionary response to the fire, said Cameron McRae, the district's director of transportation, maintenance and operations.
All Nye County schools were expected to open Tuesday.
The US Ecology site has served as a dump for low-level radioactive waste and other hazardous materials since the early 1960s.
From 1983 to 1992, solid low-level radioactive waste primarily from hospitals and university research labs was buried there in dirt-covered trenches. It came from Nevada, Colorado and New Mexico, the states that make up the Rocky Mountain Low-Level Radioactive Waste Board compact, according to Leonard Slosky, the board's executive director.
US Ecology stopped accepting radioactive waste in 1992, but it still takes in about 100,000 tons of hazardous waste per year from out-of-state and in-state sources.
A fire in one of the disposal trenches or in a facility near them would be "very unusual" because there are supposed to be no ignition sources in or around the waste, Slosky said.
Mulvihill said the fire burned a 40-to-50-foot area of the 40-acre site on state-owned land.
As part of their investigation, state officials said they will be looking at the overall stability of the more than 50-year-old dump.
The fire prompted a coordinated emergency response from Nye County and from Nevada's Department of Health and Human Services, Department of Public Safety, Highway Patrol, State Fire Marshal, National Guard, Department of Transportation, and Division of Environment Protection.
The U.S. Environmental Protection Agency also sent an on-scene coordinator to the site.
In 2010, the EPA fined US Ecology nearly $500,000 for 18 hazardous waste violations.
Reports on the violations said that on at least two occasions operators observed smoke coming from a soils decontamination heating unit that resulted in the release of hazardous compounds into the air.
Inspectors also noted "six spills, leaks or other uncontrolled PCB discharges" between 2006 and 2008 that weren't reported as required by law, according to an EPA news release in 2010.
PCBs, or polychlorinated biphenyls, are toxic, organic pollutants that persist in the environment. They were once widely used in electrical transformers and capacitors but are no longer produced in the United States.
Reporter Ricardo Torres contributed. Contact Henry Brean at email@example.com or 702-383-0350. Find him on Twitter: @RefriedBrean. Contact Keith Rogers at firstname.lastname@example.org or 702-383-0308. Find him on Twitter: @KeithRogers2