Federal contractors plan to install another level of containment over the tunnel that caved in at the Hanford nuclear site on May 9. The tunnel was used to store old, highly radioactive equipment from a facility that dates back to the Cold War.

As soon as the wind dies down, contractors are going to cover the oldest underground tunnel at Hanford’s PUREX plant—a facility that processed plutonium for nuclear bombs—with a plastic covering. They’re going to anchor it in place with big concrete blocks on both sides.

The idea is to keep any radioactive contamination at the site. They don’t want things to dust up. The plastic might help keep the rainwater out of the eight-feet soil layer above the old tunnel. And that could decrease the load and maybe make the tunnel structure more stable.