Hanford crews are laying 1.8 acres of modified asphalt this week over a tank farm where five underground tanks are suspected of leaking radioactive and hazardous chemical waste.
It may look like a parking lot -- one larger than a football field and dotted by monitoring stations and risers from underground tanks. But its goal is to keep contaminated soil in the tank farm dry.
"We don't want the situation to get worse," said Dan Parker, project manager of the work for Washington River Protection Solutions. "The barrier will keep rain water and snow melt from entering the soil and carrying contamination towards ground water."
The barrier, being paid for with economic stimulus money, will be the second one built at the Hanford tank farms, where 53 million gallons of waste are stored in groups of underground tanks called "farms." The waste is left from the past production of plutonium for the nation's nuclear weapons program.
The barrier under construction now is going over the TY Tank Farm, where six single-shell tanks were built in 1951. Each tank has a capacity of 750,000 gallons.
As much liquid waste as possible has been pumped out of the tanks into newer double-shell tanks and they are not believed to be leaking now. But past leaks or spills at the tank farm are believed to have contributed to an estimated 1 million gallons of waste that have contaminated soil.
The first barrier constructed over T Tank Farm, which is Hanford's oldest group of tanks, is performing as expected, according to the Department of Energy's tank farm contractor. With the barrier in place for two years, monitors show soil beneath the barrier is drying, said spokesman Mike Berriochoa.
The T Farm barrier was constructed of polyurea plastic similar to the substance used to line pickup beds.
But at the TY Tank Farm, a modified asphalt barrier is being tried following discussions among Washington River Protection Solutions, DOE and the Washington State Department of Ecology, which is the regulator on the project.
The TY Tank Farm is better suited to the heavier weight of the asphalt. It is flatter than the T Tank Farm, so less dirt must be piled over the tanks to create an even and slightly sloped surface to prevent water from collecting on the cap.
The asphalt, which is laid in a 4-inch-thick sheet, has been modified with a polymer to produce a material that is waterproof, weathers without cracking and compacts better than conventional asphalt.
Precipitation collected on the TY Tank Farm barrier will be piped to a nearby lined basin. The water will be distributed by a piping system in the bottom of the basin and then sucked up by native grasses planted on top of the basin.
"It acts like a flower pot in a water dish," Parker said.
Fowler General Construction of Richland has a contract of nearly $3 million for the construction. Work began in February to install monitoring instruments for the barrier and the barrier should be completed by the end of September to meet a proposed legally binding deadline negotiated by DOE and its regulators.
DOE could install up to six of the barriers, with the design of the next barrier done by June.
"For environmental protection, it is a really good step," Parker said.
The barriers are a temporary measure authorized by the legally binding Tri-Party Agreement, but their protection could be needed for decades.
DOE still must decide how to clean up or otherwise permanently protect the public and environment from remains of the spills after the tanks are emptied of waste.