Environmental activists and an ex-FBI agent are trying to block the long-planned opening of the Rocky Flats former nuclear weapons site for recreation, arguing that hikers and bikers could inhale deadly plutonium particles and that the government skipped a required investigation.

Their legal challenge, filed Tuesday in federal court, intensifies the latest eruption of public mistrust around one of the nation’s murkiest Cold War sites where, despite decades of studies and a $7.7 billion Super Fund cleanup, questions remain about whether plutonium levels in soil are safe for people.

Groups opposed to using the Rocky Flats National Wildlife Refuge for recreation recently enlisted public schools leaders in seven districts who have banned or require special permission for children to go there on field trips. Activists are pressing five more districts, including Aurora Public Schools, to ban visits.

Colorado Department of Public Health and Environment officials on Tuesday reiterated their assessment that Rocky Flats, on wind-whipped grasslands 16 miles northwest of Denver, no longer contains plutonium at dangerous levels. The health department and Environmental Protection Agency oversaw cleanup after FBI raids in 1989 exposed mismanagement, environmental law violations, and lying that led to closure and eventual criminal convictions.

EPA regional administrator Doug Benevento, who worked for nearly a decade as the state’s health chief on the cleanup, on Tuesday declared the refuge “safe for everyone.” He backed up the CDPHE’s assessment of the site as “suitable for unlimited use and unrestricted exposure.”

He said the latest federal review of the site, done last summer, “again affirmed the area as safe for unlimited use.”

But project opponents aren’t buying it.

“If they get away with what they are trying to do here, that will be the standard for 20 other Department of Energy sites around the country. This would have health implications for multiple generations of people who recreate on these sites. It is a gamble,” said University of Colorado emeritus biology professor Harvey Nichols, who in the 1970s measured soil and snow contamination at Rocky Flats under federal contract.

Jeff Neumann, Denver Post

Former FBI Special Agent Jon Lipsky, who led the 1989 raids, joined attorney Randall Weiner and groups — including the Rocky Mountain Peace and Justice Center, Rocky Flats Right to Know and others — after Weiner filed the lawsuit in U.S. District Court.

“That plutonium dust is all over the site. It can potentially kill people. It is a coverup,” said Lipsky, 63, who retired from the FBI in 2004.

Mistrust of the government’s handling of Rocky Flats “hasn’t died,” he said, “because they didn’t clean it up to a safe level.” The wildlife refuge soil, as well as dirt around the adjacent Candelas housing development, was never treated, he said.

Rocky Flats factory workers used plutonium to make triggers for nuclear warheads that the U.S. military wielded to deter the Soviet Union. Hundreds of workers suffered from cancer and other ailments linked to their exposure to radioactive materials. The cleanup entailed burying buildings, including some so contaminated that plutonium concentrations were deemed “infinity” because they couldn’t be measured.

Then the feds used a negotiated cleanup standard of 50 picocuries per gram of dirt to guide soil cleanup inside a 1,308-acre core area that remains fenced. Beyond that area — where refuge trails would bring hikers, horse riders and cyclists starting this summer — no soil cleanup was done.

Thousands of soil tests conducted after 1991, during the Superfund cleanup and afterward, found no “hot spots” with plutonium levels higher than 20 picocuries, state officials said, and the average plutonium level in surface dirt outside the core area at the refuge is 1.1 picocuries per gram.

The issue is whether risks to people have been reviewed as required under the National Environmental Policy Act before opening the wildlife refuge for recreation.

A federal conservation plan and environmental impact statement issued in 2004 presented plans for managing Rocky Flats as a wildlife refuge that could include public hiking trails. In 2007, the Department of Energy transferred 3,953 acres, not including core, to the U.S. Fish and Wildlife Service to establish the refuge. Fish and Wildlife on March 23 formally announced where trails would be located with 15 public entry points around the refuge.

“The Rocky Flats Refuge is safe for any use — for refuge workers, visitors and even full-time residents,” CDPHE corrective action official Carl Spreng said.

“Future users of the site, like refuge workers and visitors, face negligible risks — far less than many risks we all face daily,” he said. “Extensive sampling and careful, conservative calculations led to the conclusion that present conditions at the site are protective of human health. Opening the refuge to visitors will allow this area, once the most contaminated spot in Colorado, to be enjoyed as an asset.”

Some environmental activists contend Rocky Flats should remain off-limits for people forever.

The lawsuit questions the 50-picocuries limit, higher than plutonium limits set for cleanups at other Cold War sites, and asks a federal judge to order Fish and Wildlife to conduct a review of potential impacts should the site be opened to people this summer.

Fish and Wildlife officials declined to discuss the issue on the record.

“By making the preposterous assumption that land in the buffer zone of the old nuclear facility was transferred to USFWS in clean condition, even though it underwent no remediation, USFWS evaded its obligations under NEPA to look at alternatives to, and the environmental consequences of, placing trails where residual plutonium contamination lingers,” the 39-page complaint says.

In Boulder on Tuesday, environmental groups demanded independent scientific analysis of risks to people using trails.

“It is unacceptable to have children on land where there is plutonium,” Rocky Mountain Justice and Peace coordinator Chris Allred said.

Part of the problem in determining safety for recreation is finding spots “where plutonium may have been dumped,” Weiner said.

“We expect our federal agencies to look out for our best interests — not to hide mistakes of the past under a misplaced plan to create recreation sites,” he said.