The prescribed fires to restore overgrown forests and grasslands near homes in Colorado have hit a snag: plutonium and its perception at a former nuclear weapons site upwind of Denver.

West metro leaders are opposing a long-planned federal burn in March on 701 acres at Rocky Flats, once a Cold War bomb trigger factory, where plutonium contamination created an environmental disaster.

After a $7 billion cleanup, completed in 2005, Rocky Flats became a 4,000-acre national wildlife refuge, which still remains closed to the public.

Worried residents contend the controlled burn to improve grasslands for elk and raptors could have a deadly impact on people by releasing plutonium into the air.

Federal authorities at a meeting this week tried to reassure residents the burn is safe and essential to restore ecological health of tallgrass prairie and protect proliferating homes in a massive new Candelas housing development.

The fire is part of a wide controlled-fire effort by federal and state land managers, gaining momentum this winter, to rejuvenate forests and reduce the risk of catastrophic wildfires.

The Colorado Department of Public Health and Environment has given the green light to the proposed Rocky Flats burn, issuing a required air permit.

“The national refuge system would never have taken this land if there was a risk. All the lands we manage at Rocky Flats have no use restraints; they studied fire and fire was deemed an acceptable use,” said Dave Lucas, refuge manager for the U.S. Fish and Wildlife Service.

“The Flats evolved with fire. It used to burn. It is going to burn. We’re trying to treat that area of the refuge before they finish building those houses. It will make it safer to fight wildfires in that area on our terms. We want to do it before those houses get done.”

Federal and state officials at a public meeting this week assured residents that soil sampling shows plutonium levels at the refuge are safe, no higher than “background” plutonium found elsewhere in metro Denver.

Soil tests by federal contractors in the proposed burn area were done between 1992 and 2004, CDPHE spokesman Mark Salley said, and the “risk of spreading contamination from burning in this portion of the refuge is essentially no different from burning anywhere else along the Front Range.”

But residents are unswayed in west metro suburbs — including Arvada, Superior, Westminster and Northglenn — some saying they don’t trust the government data. They’ve petitioned Fish and Wildlife to prevent the burn. They planned to meet Thursday with lawyers to discuss options.

“Plutonium is attached to the soil out there,” said Mickey Harlow, 73, an Arvada resident who has lived five miles east of Rocky Flats for 30 years, one of four people on her block diagnosed with cancer.

“It’s too risky to be burning there. Is it appropriate to burn on radionuclides-contaminated sites? There are other ways of controlling weeds.”

A controlled burn to protect new housing “would release plutonium particles,” said LeRoy Moore, 83, a longtime activist with the Rocky Mountain Peace and Justice group. “Wherever the wind takes it, that’s where it will go. It’s unpredictable what the wind will do here in Colorado. It could pick up plutonium and carry it all the way across Denver, as it has done in the past.

“So they’re taking a chance of exposing people if they burn. … If plutonium is released, it would be in the form of tiny particles suspended in the air. These could be inhaled. Even a single particle could destroy someone’s health.”

The 14-member Rocky Flats Stewardship Council of west metro leaders representing 900,000 metro residents has asked Fish and Wildlife to cancel the burn. This opposition is based not on risk but on public perception and concern, executive director David Abelson said.

“You should not treat this refuge like other refuges,” Abelson said. “There’s a lot of community interest and concern that warrants a nontraditional approach to land-management issues.”

Federal officials said they haven’t made a final decision. While they see controlled fire as the best option, they’ll evaluate other possibilities such as mowing or deploying goats.

But the risk of plutonium inhalation is so low that even firefighters making sure the burn does not spread beyond 701 acres would not need special protective equipment, Lucas said.

“We know we need to do something,” he said. “We’re not going to dismiss folks’ feelings. We’re trying to make the right decision.”

Bruce Finley: 303-954-1700, bfinley@denverpost.com or twitter.com/finleybruce