The U.S. Department of Energy is launching a federal investigation into a demolition site at the Hanford nuclear reservation where radioactive waste has been spreading in unexplained ways.

Called the Plutonium Finishing Plant, it’s a massive factory building that the government is trying to tear down. But since last year, 42 demolition workers have been found to have radioactive contamination in their bodies, dozens of cars were contaminated and more windblown specks of radioactive waste were found near a public highway.

The demo project has been idle since the winter — even though the project is a year behind its “slab on grade” deadline. The Washington state Department of Ecology and EPA have called for work to stop until officials can prove contamination won’t spread further.

Now, an arm of the U.S. Department of Energy is looking into the whole thing.

In a recent letter, the department informed the contractor in charge of the demolition, CH2M Hill, it is requesting documents and will be coming to town to interview workers.

The DOE continues to work on shoring up a large debris pile that is thought to be the source of much of this escaped material. It’s also doing a “root cause evaluation” and studying what can be done to safely complete the demolition.

The Plutonium Finishing Plant was a large factory at Hanford that turned liquids containing plutonium into solid plutonium “buttons” during the Cold War.