Workers at the Hanford nuclear reservation are starting to install a thick plastic covering over a tunnel that collapsed on May 9. That tunnel holds highly radioactive waste left over from the Cold War.

The tarp is intended to serve two purposes: Protect the environment and workers if further collapse happens, and keep rainwater out of the 8 feet of soil above the tunnel lightening the load.

Workers have been removing material like fence posts and power poles from near the tunnel in preparation for the covering. 

The federal government and its contractor are making longer term plans for the tunnels and the results are expected to be public in the next few months.

The tunnel that caved in, known as Tunnel 1, is one of two train tunnels that were built to service the PUREX plant—a factory that processed plutonium for use in atomic bombs during the Cold War. The tunnel was built in the 1950s out of concrete and creosoted train ties.

Hanford officials have said the age of the tunnel, the very wet winter and spring, the construction techniques and the materials used in the old tunnel might have contributed to its collapse.

Meanwhile, Washington Gov. Jay Inslee and Oregon Gov. Kate Brown have asked for more federal cleanup money for Hanford. States expect President Donald Trump to release a more detailed budget proposal next week.