Asphalt to cap Hanford tanks

KENNEWICK — Work has begun on putting an asphalt cap larger than a football field over a radioactively contaminated area of central Hanford.

It's the second cap to be placed over a portion of the Hanford nuclear reservation, where underground tanks holding millions of gallons of radioactive and hazardous chemical waste have previously leaked into the soil.

The caps are intended to prevent moisture from rain or snow runoff from seeping into the soil and driving contamination deeper or into the groundwater.

The Department of Energy and its regulators are discussing placing as many as six of the caps over portions of the tank farms, where an estimated 1 million gallons of tank waste has leaked into the soil.

They're only a temporary measure, but their protection could be needed for decades.

"It's the right thing to do to protect the environment," said Dan Parker, the Washington River Protection Solutions manager for the second cap.

The Energy Department has not made a decision on how to clean up or otherwise permanently protect the public and environment from remains of the spills after the tanks are emptied of the waste.

The latest proposal for legal deadlines under the Tri-Party Agreement calls for Hanford's 149 oldest tanks — built with single rather than double shells — to be completed by 2040.

The first cap, which covered 70,000 square feet, was built at Hanford's oldest group of tanks, T Farm. It's home to Tank T-106, which is believed to have leaked an estimated 115,000 gallons of waste in 1973.

There is just one year of data from the project, and measurements are at the low end of the scale of what can be detected. But there appears to be very little change in the moisture of the soil under the barrier, said Joseph Caggiano, a hydrologist for the state Ecology Department.

Work is under way to install monitoring instruments for the second cap, which will cover the entire TY Tank Farm in central Hanford.

Money for the project comes from the $1.96 billion in federal economic-stimulus money for Hanford cleanup work.

The TY Tank Farm includes six underground tanks built in 1951. All but one are suspected of leaking in the past.

Although they still contain sludge, the pumpable liquids have been emptied from the tanks.

The first cap, built by the previous tank-farm contractor, was constructed of polyurea plastic similar to the substance used to line pickup truck beds.

However, Washington River Protection Solutions is building the second cap out of asphalt modified to be resistant to liquid.

"We went through a new material-selection process with the Department of Energy and the Department of Ecology and determined that a modified asphalt material will work better for the TY Farm," Parker said.

Asphalt has a history of industrial use as a cap or barrier over contaminated sites, he said.