ROCKY FLATS, Colo. ― Plutonium, named for the Roman god of the underworld and the dwarf planet at the edge of the solar system, is one of the world’s most dangerous elements. Inhaling just one particle will bombard internal organs, particularly the lungs and liver, with harmful alpha radiation for decades. For the most part, it isn’t naturally occurring. But until just over a decade ago, it was plentiful in this 5,000-acre patch of rolling hills and grasslands.

From 1952 to 1989, this picturesque sanctuary was home to a factory that produced plutonium triggers for nuclear weapons ― a lot of them. Nearly all of the approximately 70,000 nuclear weapons produced in the United States include a part made at Rocky Flats.

It was designated as a Superfund site in the early 1990s, and the radioactive materials have been removed. It’s scheduled to open to the public for the first time next summer.

But rather than welcoming the prospect of thousands of new acres for recreation, some Coloradans are suing to stop it.

Looking north from Rocky Flats’ northern border.

Five environmental groups and community organizations filed a lawsuit in May to prevent the U.S. Fish and Wildlife Service from moving forward with plans to build a visitors center, hiking trails and other recreational infrastructure on the site, saying the government hasn’t scrutinized the property closely enough to begin construction. The suit argues that it’s difficult to prove a site is “clean enough” after removing 40 years’ worth of nuclear waste ― and, what’s more, that USFWS hasn’t met its legal obligation in demonstrating that cleanliness to the public.

“You have highly contaminated plutonium-laced soil that’s down deep that is going to eventually migrate to the surface and be blown into the region. It’s a concern,” said Randall Weiner, a Boulder-based lawyer representing the plaintiffs in the case. “At a minimum the agency should be looking at issues like that… before they open the refuge to the public.”

Rocky Flats on June 9, 1989, three days after FBI agents raided the Department of Energy site.

The Rocky Flats Plant had a long record of environmental blunders, aided by a Cold War-era government eager for more nuclear weapons at any cost.

“Things were blatantly unsafe. There were blatant violations of procedure,” Jacque Brever, a nuclear technician at the plant, recalled for a book on Rocky Flats published in 2004. “It was the height of the nuclear weapons production era… Everything was compromised for the sake of nuclear weapons production.”

Brever had approached the FBI as a whistleblower on the plant’s violations. She said her fellow workers thanked her by contaminating her protective equipment with radioactive material. She ultimately developed thyroid cancer and died in 2015.

In 1957 and 1969, out-of-control fires at the factory nearly resulted in catastrophe. Both fires sent plumes of radioactive waste into the air, contaminating miles of land downwind. Officials never notified the public of the first fire ― only acknowledging it more than a decade after the fact, when scientists from the nearby University of Colorado tested land near Rocky Flats and noted that the plutonium contamination was “the highest ever measured near an urban area, including the city of Nagasaki.”

A fire at the Dow Chemical Co. Rocky Flats plant Sunday released a small amount of radioactive plutonium contamination, a plant spokesman said. He said the fire broke out in a production building. The cause of the blaze was not known.

View from inside an input-output station at Rocky Flats in 1988.

The plant was particularly prone to fires ― more than 200 occurred over the course of 40 years ― as weapons-grade plutonium can spontaneously combust. Those fires, along with inadequate storage procedures and regular day-to-day operations, also released uranium, beryllium, tritium and carbon tetrachloride, a carcinogenic cleaning solvent, into the area.

And not in trace amounts, either. Under the oversight of Dow Chemical and, later, Rockwell International, plant operators lost track of more than 2,600 pounds of plutonium and other radioactive material, as documented in later lawsuits and a Government Accountability Office assessment. In 1990, a full 62 pounds’ worth of plutonium was found distributed in the vents and piping of one building at the plant ― reportedly enough to manufacture six or seven nuclear bombs. Dow and Rockwell argued that just because they couldn’t find the unaccounted-for material didn’t mean they’d disposed of it improperly.

The facility left behind more than 8,000 different chemicals, many of which leached into the soil. One outdoor area alone housed around 5,000 30- and 50-gallon steel drums of plutonium and uranium-contaminated waste. These corroding drums leaked an estimated 5,000 gallons of contaminated waste oil.

The west gate of the Rocky Flats Plant on Dec. 31, 1989.

On the morning of June 6, 1989, more than 70 armed agents from the FBI, the Environmental Protection Agency and the Department of Justice stormed Rocky Flats as part of “Operation Desert Glow.”

Jon Lipsky, a retired FBI agent who led the raid, told HuffPost they used a ruse to get inside the highly secured facility.

“A week before, the ‘Earth First’ environmental group tried to take down a nuclear power plant in Arizona,” Lipsky recalled. “So we used that to call for a security briefing.”

Once inside, the FBI revealed there was no briefing. Instead, they said, a federal judge in Denver had signed a warrant that morning to allow them to search the complex. It was the first time in U.S. history that one federal agency raided another.

Lipsky’s primary target was Building 771.

Library of Congress

One of 800 structures on the site, Building 771 was built in the early 1950s as a plutonium foundry, for metallurgical research and recovering plutonium from other scrap metal. Work there occurred around the clock, three shifts a day, for nearly four decades, processing as much as 1,100 pounds of plutonium per month.

At the heart of the building was an incinerator. The FBI believed Rocky Flats’ corporate manager at the time, Rockwell International, was using this incinerator to illegally burn hazardous waste ― and that the Department of Energy, which ultimately oversaw operations at the plant, was ignoring it.

A view of the incinerator in Rocky Flats Building 771 in 1988.

A report commissioned in 1992 to help guide cleanup efforts attempted to track down and document every recorded safety incident in the building’s history. The resulting paper is 32 pages long and includes everything from the mundane (“Employee playing volleyball. Sprained ankle”) to the alarming (“Flowmeter ruptured, operator sprayed with contaminated caustic and steam”).

Decades later, cleanup crews would nickname the most radioactive section of Building 771 the “infinity room,” because the radiation there exceeded their Geiger counters’ ability to measure it ― causing them to warn instead of an “infinite” amount of radiation.

Ultimately, the raid led to a four-year federal grand jury hearing, which indicted Rockwell and eight individuals for their environmental crimes. Then-U.S. Attorney…