RICHLAND, Wash. — Removing radioactive waste from underground tanks at the nation’s most contaminated nuclear site has proved to be technologically vexing for years, and recent word that six tanks are leaking has only added pressure to efforts to empty them.
A proposal to ship some of that waste to New Mexico to ultimately stem the leaks earned approval from Washington Governor Jay Inslee, who called it the right step for south-central Washington’s Hanford Nuclear Reservation, the state, and the nation.
The proposal requires approval from the two states, and Congress still must approve funding — likely pushing any shipments of waste two to four years into the future. But Inslee said he will press lawmakers to fully pay for the proposal, saying ‘‘every single dollar of it is justified.’’
Federal officials on Wednesday announced a plan to ship some million gallons of radioactive waste from Hanford for disposal in a massive repository — called the Waste Isolation Pilot Plant — near Carlsbad, N.M., where radioactive materials are buried in rooms excavated in vast salt beds nearly a half-mile underground.
The waste near Carlsbad includes such items as clothing, tools, and other debris.
The Hanford site sent the equivalent of about 25,000 drums of such so-called transuranic waste, which is radioactive but less deadly than the worst, high-level waste, to the site between 2000 and 2011.
The latest proposal would target transuranic waste in underground tanks that hold a toxic, radioactive stew of liquids, sludge, and solids, but it would address only a fraction of the 56 million gallons of total waste in the tanks.
The proposal quickly met with criticism from a New Mexico environmental group that said the state permit allowing the government to bury waste at the plant would not allow for these shipments from Hanford.
Senator Tom Udall, a New Mexico Democrat, said the site specifically prohibits such waste from Hanford and any proposal to modify permit language in this case would need ‘‘strong justification and public input.’’
“With regard to Hanford waste, I urge all parties involved to exhibit caution and scientific integrity to ensure that DOE is abiding by the law and that the waste classifications are justified,’’ Udall said in a statement.
Dave Huizenga, head of the Energy Department’s environmental management program, said the transfer would not impact the safe operations of the New Mexico facility.
‘‘This alternative, if selected for implementation in a record of decision, could enable the department to reduce potential health and environmental risk in Washington state,’’ said Huizenga.
Don Hancock, of the Albuquerque-based watchdog group Southwest Research and Information Center, which opposes the transfer to New Mexico, said this is not the first time the Energy Department has proposed bringing more waste to the plant near Carlsbad.
‘‘This is a bad, old idea that’s been uniformly rejected on a bipartisan basis by politicians when it came up in the past, and it’s been strongly opposed by citizen groups like mine and others,’’ Hancock said. ‘‘It’s also clear that it’s illegal.’’
Disposal operations near Carlsbad began in March 1999. Since then, more than 85,000 cubic meters of waste have been shipped to it from a dozen sites across the country.
Any additional waste from Hanford would have to be analyzed to ensure it could be stored at the site because a permit issued by the New Mexico Environment Department dictates what kinds of waste and the volumes that can be stored there.
Deb Gill, a spokeswoman for the site, said the facility does not anticipate any problems with its existing capacity as permitted under law.
Officials estimate that some 7,000 to 40,000 drums of waste would be trucked to New Mexico, depending on how the waste is treated and its final form.
South-central Washington’s Hanford Nuclear Reservation has 177 underground tanks, which hold toxic and radioactive waste left from decades of plutonium production for the country’s nuclear weapons arsenal. The tanks have long surpassed their intended 20-year span.
Federal officials have identified six leaking tanks. Five of them contain transuranic waste and are among the tanks being targeted under the plan.
The Energy Department has said the leaking tanks could be releasing as much as 1,000 gallons a year. Officials said the leaks pose no immediate threat.