Containers filled with radioactive waste continue to stack up in the desert west of Idaho Falls.

There are nearly 20,000 steel drums filled with the transuranic waste, waiting to find a permanent resting place. The waste is in a holding pattern as a New Mexico nuclear waste repository slowly recovers from a pair of 2014 accidents.

The Waste Isolation Pilot Plant near Carlsbad, N.M. is scheduled to reopen to limited operations in December, U.S. Department of Energy officials told the Idaho National Laboratory Site Citizens Advisory Board last week.

But DOE officials said there is still much uncertainty about when Idaho will be cleared to begin shipping out its growing stockpile of waste. That’s because even when the repository known as WIPP reopens, it’s still not expected to be back at full strength for several more years as additional repairs are made. In addition, other federal facilities around the country will be hoping to send their growing waste collections all at once, too, creating a bottleneck.

“I think it’s fair to say that once does WIPP does resume operations, it will be at a much slower pace than what we were accustomed to before the shutdown,” said Brad Bugger, a supervisor at DOE’s Idaho Operations Office.

That continued uncertainty about when the waste will leave Idaho has led to new concerns that the DOE will miss another state-mandated cleanup milestone in the 1995 Settlement Agreement. The agreement said the transuranic waste — which continues to be slowly uncovered and repackaged at the desert site — needs to be gone from the state by the end of 2018.

“It’s going to be a challenge,” to meet the deadline, said Susan Burke, INL coordinator for the Idaho Department of Environmental Quality. She added that continuing to process and package the waste into drums — even if it can’t yet be shipped outside Idaho — is still safer for the environment and human health than leaving it in place.

The waste includes tools, rags, clothing, sludge and dirt — anything contaminated with a transuranic element such as plutonium. Most of it came from the now-closed Rocky Flats Plant outside Denver, where nuclear weapon components were made.

Truckloads of waste, held in wooden and fiberglass boxes and metal drums, were shipped to the site in the 1970s and ’80s, where it was dumped and covered over with dirt. For years DOE cleanup contractors have been working to carefully clean up the mess that was left behind.

In a recent interview, Idaho Attorney General Lawrence Wasden said he is keeping an eye on the approaching 2018 deadline. DOE is already out of compliance with the Settlement Agreement due to liquid waste that was supposed to be treated by 2012. The department also is in violation of a Settlement Agreement requirement to ship a running average of 2,000 cubic meters of transuranic waste out of the state each year.

“I certainly believe we have time right now if the Department of Energy is willing — and we’re trying to engage them in conversation about that 2018 deadline — that we can find a way to resolve some of that,” Wasden said. “One of those (ways to resolve the problem) would be to have a prioritization of shipments to WIPP once it is open.”