JEFFERSON COUNTY, Colo. — A plan to allow the public onto the outskirts of a former nuclear weapons plant that’s now a wildlife refuge ran into another court challenge Tuesday.

Environmental and community activists filed suit in federal court saying Rocky Flats National Wildlife Refuge outside Denver is too dangerous because of the potential presence of plutonium and other hazardous materials.

The lawsuit says the U.S. Fish and Wildlife Service did not complete a required analysis of environmental risks.

The lawsuit also claims the agency did not examine contamination on about one square mile recently added to the refuge.

The Fish and Wildlife Service said in a statement it does not comment on pending lawsuits, but the agency said it would not open the refuge to the public if it was unsafe.

The activists’ previous suit was dismissed in September when a judge said it was premature.

In March, the Fish and Wildlife Service formally announced plans to build trails and a visitors center at the refuge and open them to the public, prompting the groups to sue again.

The refuge encompasses 8 square miles that served as a buffer zone around the weapons plant. The plant site itself is off-limits to the public.

Sitting on a windy mesa west of Denver, Rocky Flats manufactured plutonium triggers for nuclear warheads until it closed in 1989 because of safety and environmental concerns.

It became a refuge in 2007 after a $7 billion cleanup.

The lawsuit was filed by Rocky Mountain Peace and Justice Center, Candelas Glows, Rocky Flats Right to Know, Rocky Flats Neighborhood Association and Environmental Information Network.

Last week, the Denver Public Schools board barred school-sanctioned field trips to refuge, saying it is too much of a risk.

School boards and administrators have imposed similar bans in the Boulder Valley, St. Vrain Valley, Adams 12 Five Star, Adams 14, Westminster and Jefferson County school districts.