LAS VEGAS — Radiation wasn’t immediately detected during fly-overs of a burned trench containing long-buried radioactive waste at a commercial disposal site in rural southern Nevada, state and federal officials said Monday.

Ground testing was scheduled next, headed by a U.S. Environmental Protection Agency radiological emergency team sent to the site about 115 miles northwest of Las Vegas, said Rusty Harris-Bishop, spokesman for the EPA Region 9 office in San Francisco.

“No gamma radiation has been detected at this time,” Harris-Bishop said in a statement announcing the federal agency was joining a damage and danger assessment headed by the state and involving the Nevada National Guard, Nye County officials and U.S. Energy Department.

The EPA said the unknown amount of low-level radioactive waste that burned had been deposited sometime in the 30 year-period before 1992, when facility operator US Ecology stopped accepting such material. It was one of six in the nation that accepted low-level radioactive waste, which typically includes tools, protective clothing, and parts and machinery from nuclear plants.

The fire was out by Monday morning and no injuries were reported, said Bud Marshall, southern Nevada regional supervisor for the state Division of Emergency Management and Homeland Security.

Nye County Sheriff Sharon Wehrly said in a statement Monday evening that U.S. 95, a key north-south highway past the site, was reopened after ground and air testing found no contamination.

The closure had stretched nearly 140 miles, from State Highway 160 in the Pahrump area to U.S. 6 in the county seat of Tonopah. Several other roads were still closed, in part due to storm damage.

The Nye County School District shut its two closest schools in Beatty because of the fire, but was set to reopen on Tuesday.

Officials said the closures affected about 400 students.

Gov. Brian Sandoval activated the state Emergency Operations Center in Carson City to coordinate the response.

Aerial testing was conducted Monday with a twin-engine airplane and a helicopter from the former Nevada Test Site flew, Nevada National Security Site spokesman Darwin Morgan said.

A four-member Nevada Guard hazardous materials detection team arrived for ground testing, Maj. Mickey Kirschenbaum said.

It wasn’t clear how the fire started. The shuttered disposal site is about 8 miles from populated areas. The area is under state Department of Health and Human Services jurisdiction.

US Ecology employs 52 people and operates an adjacent plant to treat, recycle and dispose of hazardous and nonhazardous waste from commercial and government entities.

The EPA in 2012 permitted US Ecology to accept toxic polychlorinated biphenyl, or PCB, waste. Harris-Bishop said that permit remains current. PCBs were manufactured and used for 50 years as liquid insulation in electrical transformers but were banned in 1979.

US Ecology spokesman Dave Crumrine said a company operations manager reported the fire about 1 p.m. Sunday, and no evacuations were ordered.

The fire was reported to Nye County officials a little after 2:30 p.m., sheriff Sgt. David Boruchowitz said.

The radioactive waste dump consists of 22 trenches up to 800 feet long and 50 feet deep. Older trenches have waste within 3 feet of the ground surface, according to a 1994 history prepared for the federal Energy Department by the Idaho National Engineering Laboratory. Waste in more recent trenches is at least 8 feet deep.

The 80-acre site was the first commercially operated radioactive waste disposal facility licensed by the federal government, according to the Idaho lab report.

Nevada leases a 400-acre buffer zone around it from the federal Bureau of Land Management, according to a Nevada Division of Environmental Protection fact sheet.