Hanford employees began work to remove radioactive sludge from a storage facility near the Columbia River and move it to a location near the center of the Hanford site, the U.S. Department of Energy announced Wednesday.

The 35 cubic yards of sludge are a mixture of tiny fuel corrosion particles, metal fragments, and dirt. It’s the result of deteriorating fuel rods that were exposed to radiation and is some of the most hazardous material at Hanford, according to the Department of Energy.

The sludge is currently stored in a facility about 400 yards from the Columbia River.

Workers will first pump the sludge to an adjacent building where they will package and prepare the material to be transported to the middle of the Hanford site. The work is expected to last until 2019.

WATCH: Hanford workers begin sludge removal

The new storage facility has safety features including secondary containment basins, leak detectors, and vents.

The move away from the Columbia River and to a safer storage facility is to reduce risk, according to Doug Shoop, manager of the Department of Energy’s Richland Operations Office.

Hanford’s contractor, CH2M HILL Plateau Remediation Company, says workers spent years developing the sludge removal system and took extensive preparations before the work began.