Environmentalists and community activists are trying to persuade a judge that the public might not be safe on a Colorado wildlife refuge that used to be a buffer zone around a nuclear weapons plant.

The judge scheduled a hearing in Denver federal court Tuesday on whether to grant a preliminary injunction barring the U.S. Fish and Wildlife Service from opening Rocky Flats National Wildlife Refuge to the public this summer. The refuge is just west of Denver.

The activists filed a lawsuit claiming the agency didn’t adequately study the safety of the site. They want the judge to keep the refuge closed until the lawsuit is decided.

The government says the site is safe.

A plant at the center of the site manufactured nuclear bombs components. The government spent $7 billion cleaning it up.