Washington agreed this week that the Department of Energy had met the 2010 consent decree requirements for emptying one more tank of radioactive waste.
That brought DOE closer to meeting the consent decree deadline to empty the 16 single-shell tanks in the group called C Tank Farm by Tuesday, the end of the federal fiscal year.
But three leak-prone, single-shell tanks remained out of compliance as the deadline passed. DOE had warned the state that it was at serious risk of missing the deadline.
The 13th and latest tank to meet requirements of the consent decree is Tank C-112, which has about 13,000 gallons of waste remaining after Hanford workers removed about 91,000 gallons.
The goal is to have no more than 2,700 gallons of waste remaining, which is about 1 inch of waste if it were spread across the bottom of the 530,000-gallon tank.
But the consent decree allows the state Department of Ecology to waive that requirement if three technologies have been used to their limit to remove waste in a single tank.
The waste is left from the past production of plutonium for the nation's nuclear weapons program. It is being moved from 149 leak-prone single-shell tanks into double-shell tanks for storage until it can be treated for disposal.
Washington said in a letter Monday to DOE that it had agreed two waste retrieval technologies had removed as much waste as possible in Tank C-112 and that a third technology would have limited effectiveness and would not substantially reduce the risk of the waste.
The first technology used was a telescoping sluicing system that sprayed liquid on waste to break it up and move it toward a central pump in the tank. Then, DOE contractor Washington River Protection Solutions tried soaking the waste with water and a caustic solution to remove the hard layer at the bottom.
The third proposed technology would have been another soak, but with a different chemical.
The state agreed DOE could forgo that, but DOE still must analyze samples of the remaining waste and assess the risk posed by the remaining waste.
Further retrieval may yet be required based on those results, it said. Retrieval equipment cannot be removed from Tank C-112 without state approval.
The state also wants DOE and its contractor to continue to improve technology for emptying the enclosed, underground tank.
Waste had been broken into sandlike particles in Tank C-112, but the particles could not be moved to the pump inlet and pumped out of the tank, the state said. That process will need to be improved for other tanks.
Last year DOE used a remote-controlled device, the Foldtrack, to finish emptying one of the C Farm tanks. That also was an option favored for Tank C-112, but the company that makes it has gone out of business, according to the state. DOE needs to replace that capability, the state said.
The 800-pound machine could extend to 12 feet long to fit through the narrow risers that provide the only access to the underground tanks. But once it was lowered onto the floor of the tank, it folded up to form a remote-control bulldozer with water jets.
With Tank C-112 waste retrieval complete for the purposes of the consent decree, DOE now has 14 of 149 single shell tanks retrieved, all but one of those in the C Tank Farm.
Hanford workers have removed almost 1.5 million gallons of waste from the tanks in the C Tank Farm and almost 1 million gallons from tanks in the S Tank Farm.
The 2010 consent decree also includes requirements for building and starting to operate the Hanford vitrification plant to treat up to 56 million gallons of Hanford tank waste. DOE has warned the state that all the remaining consent decree deadlines for the plant may be missed.
A 30-day window in which either DOE or the state may ask the federal court to intervene in the consent decree expires Oct. 5.
-- Annette Cary: 509-582-1533; email@example.com; Twitter: @HanfordNews