Idaho plans to fine the federal government $3,600 a day for missing a deadline to remove 900,000 gallons of liquid nuclear waste from tanks at a southeast Idaho nuclear facility, state officials said.

The state Department of Environmental Quality said it rejected a request for another extension from the U.S. Department of Energy to go past the Dec. 31 deadline to remove the radioactive waste at the Idaho National Laboratory.

Idaho officials tell the Post Register that three 50-year-old tanks are no longer supposed to be used for storage under federal laws governing hazardous waste.

"Although DOE has had many years to complete this milestone, DOE has failed to initiate and complete treatment of the liquid wastes in the tanks or construct new tanks," said DEQ's Hazardous Waste Compliance Manager Natalie Clough in a letter Tuesday to Richard Provencher, manager of DOE's Idaho Operations Office. "Completion of this work is a priority of the (DEQ), and further delays are of critical concern."

The state said fines will increase to $6,000 a day if the waste isn't gone by July 1.

Department of Energy spokeswoman Danielle Miller said the agency is reviewing the notice of violation it received. She declined to make additional comments.

The 890-square-mile nuclear facility in southeastern Idaho is known as the place where nuclear energy generated electricity for the first time, in 1951. During the Cold War, the site also became home to millions of tons of nuclear waste generated at sites in other states.

The facility sits atop the Eastern Snake Plain Aquifer, and state officials going back decades have expressed concern about potential contamination.

Clough said the aging tanks containing the liquid nuclear waste don't meet current regulatory standards, such as a secondary containment system. But Clough said there's no immediate concern about the tanks leaking.

The Department of Energy built a facility called the Integrated Waste Treatment Unit to turn the liquid waste into a powder. But the facility has continued to run into problems trying to get beyond the testing phase. In December, though, officials said operators had better test results. But it's still unknown when the liquid waste might be removed from the tanks.

"We've always been very clear that meeting these treatment goals is a state of Idaho priority," Clough said.