You can erase the pencil tanks at the Hanford Nuclear Waste Site in southeastern Washington.

More than 50 pencil tank assemblies—some two stories tall—contaminated with chemical and radiological hazards are now fully removed from Hanford’s Plutonium Finishing Plant.

The tanks, which received the moniker because of their long and narrow shape, were a key portion of final cleanup of the finishing plant. During production days, the pencil tanks reclaimed plutonium from scrap metal.

“The safe removal of the pencil tanks is important progress in cleaning out and demolishing the Plutonium Finishing Plant, which reduces risk on the Hanford Site,” Tom Teynor, federal project director for the plant, said in a statement. “We have a deadline of cleaning out and demolishing all of the buildings that make up the Plutonium Finishing Plant by the end of September 2016.”

The removal of the pencil tanks—there were 52 total assemblies comprised of 196 pencil tank units—started in 2008 when the U.S. Dept. of Energy contractor CH2M Hill started tackling the tanks that range anywhere in size from 3 ft to 22 ft long. Each tank reaches a point at the end, designed to prevent the buildup of plutonium, which could have led to dangerous situations during production.

According to Dept. of Energy information, the tanks were arranged vertically on walls inside a concrete canyon located in the Plutonium Reclamation Facility, adjacent to the Plutonium Finishing Plant. To move the pencil tanks inside the highly contaminated canyon, crews used a remotely operated crane. Use of remote operations eliminated the risk of exposing works to potentially high levels of radiation and minimized the need for manned entries into the canyon.

The crane moved pencil tanks from their operational location into a glove box in a maintenance cell of the facility where workers in protective equipment manually cut the tank into sections for disposal. A specially designed port in the canyon allowed crews to transfer the smaller pieces of the tanks for treatment and disposal.

“The talented crews worked safely and compliantly removing these pencil tanks,” Mike Swartz, vice president of the Plutonium Finishing Plant Closure Project, said in a statement. “Completing this task allows us to move into other areas of the facility that we need to prepare for demolition.”

That next stage will send workers into the canyon to remove sections of contaminated ventilation ducting and piping, steps needed to prepare the Plutonium Finishing Plant for final demolition.

Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.