Covering the ground with a durable plastic or asphalt barrier is one possible option to stop the spread of radioactive waste leaking from Hanford's underground tanks, said Jane Hedges, manager of the Department of Ecology's nuclear waste program.
Other options being considered are a second round of pumping of as much liquid waste out of single-shell tanks or possibly using new technology to get liquid and solid wastes out of the tanks and to treat it, Hedges said. She spoke Thursday in Olympia at a work session hearing of the Washington State Senate Energy, Environment and Telecommunications Committee.
The committee said it wanted the information to understand what the Legislature could do to address the problems.
In the past an estimated 1 million gallons of radioactive waste have leaked or spilled from as many as 67 of Hanford's single-shell tanks or their piping systems. Some have held radioactive waste since World War II.
When the last of the pumpable liquids were removed from the tanks in 2004, the Department of Energy believed all 149 single-shell tanks at Hanford temporarily were stabilized and that none were leaking. A new look at data on the level of waste in the tanks showed that was not the case, and the state announced this month that six of the tanks are leaking.
The waste left in the tanks now is sludge the consistency of peanut butter, with liquid trapped among solid particles, Hedges said.
Trying to pump more of the liquid out might be a possibility, she said. Just as liquid separates from organic peanut butter over time, some of the tank liquid might have become more accessible with time.
However, the tanks do not have pumps in place, and the Department of Energy would need a place to put the waste.
Single-shell tanks are being emptied into 28 newer double-shell tanks, but they are almost full, she said. In addition, a leak was confirmed this fall within the shells of the oldest double-shell tank.
She did not specify what new technologies might be available to empty single-shell tanks and treat the waste. However, Energy Secretary Steven Chu organized teams of experts to look at efficiently treating the waste before the leaks were discovered.
Among options the teams are looking at is "preconditioning" waste from some of the tanks to allow it to bypass the delay-plagued Pretreatment Facility at the vitrification plant under construction at Hanford. The plant is being built to turn up to 56 million gallons of radioactive waste into a stable glass form for disposal.
The first step at the plant is to separate waste into low-activity and high-level radioactive waste streams for separate treatment. By adding facilities in the tank farms, high-level waste might be able to be separated from some of the waste, allowing it to be treated at the vitrification plant before the Pretreatment Facility is operating.
One of Chu's teams also is looking at the possibility of sending some of the waste to the Waste Isolation Pilot Plant in the New Mexico desert, the nation's repository for transuranic waste, which typically is waste contaminated with plutonium. The waste would not need to be glassified at the vitrification plant if it were sent to New Mexico.
Adding more barriers above leaky tanks is the least complicated of the options Hedges listed.
Two of the barriers were built earlier at Hanford to prevent rain and snowmelt from driving contamination deeper into the soil toward groundwater. That contamination was left from earlier tank spills or leaks.
"It has worked very, very well," Hedges said. The barriers have markedly decreased the amount of water infiltrating the ground near the tanks, she said.
One of the barriers partially covers Tank T-111, one of the tanks believed to be leaking. The 70,000-square-foot cap was built in 2008 to cover soil contamination from a spill of 115,000 gallons of waste in 1973 from Tank T-106. It's made of the type of plastic used to line pickup truck beds.
A second cap was built in 2010 to cover about 80,500 square feet, or about 1.8 acres, over the TY Tank Farm. One of the six tanks there also is suspected of being a current leaker.