A main focus of work at the Hanford Nuclear Waste site in Eastern Washington includes crews doing everything possible to move radioactive sludge from 1940s-era single-shell underground storage tanks into more modern double-shell tanks, hopefully eliminating leaks into the soil near the Columbia River.

That plan has met its most serious hiccup yet: the likelihood of a double-shell tank now leaking.

We already knew that tank AY-102 had a problem with its inner wall, leaking waste into the 2.5-ft-wide open gap between the walls in 2012. But now we learn the outer wall isn’t so safe, either.

But the leak isn’t certain. Here’s what we do know: Dept. of Energy tests of water in a leak-detection pit near the tank showed increased levels of contamination. That likely means AY-102 has issues, but there could be a “legacy” leak that has made its way into the test area. Engineers will figure it out next.

Using additional sampling and video inspection methods, Hanford officials expect an answer on the source of the leak at some point this week.

But if early fears hold up and a double-shell tank, this one housing over 850,000 gallons of waste, has solvency issues, that only means more—and possibly unstoppable—issues for the Hanford site, a place already struggling to clean up, even with over a $2 billion annual budget.

Gov. Jay Inslee, who met with the new U.S. Energy Secretary, Ernest Moniz, just hours before finding out about the leak in a phone call last week, says he was already concerned about leaks in tanks, even before the new development.

“We will be insisting on an acceleration of remediation of all the tanks, not just AY-102,” Inslee says in a news release, continuing that DOE has a legal obligation to clean up Hanford and remove or treat waste.

At Hanford, crews have been spending over a decade trying to clean out the 149 old single-shell tanks—some of which are leaking—of 56 million gallons of waste and pumping the 28 newer double-shell tanks full of waste until a long-term storage solution can get online. That solution, a plant that will turn the sludge into vitrified glass, has been mired in budget and design issues, now projected to cost over $13 billion. In construction now, but without a final design, it won’t be fully online until at least 2022. That’s if all goes well, of course, not a common theme at Hanford.

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