Washington Closure Hanford has awarded what it expects to be its final subcontract for the completion of its cleanup work at Hanford's N Reactor.

TerranearPMC, a small Texas business with an office in Kennewick, has been given a subcontract worth $5.6 million to clean up the remaining waste sites near N Reactor.

Already, the 113 support buildings and other facilities for N Reactor have come down and the reactor has been "cocooned," or put in temporary storage. The reactor, which once produced electricity for the commercial market and plutonium for the nation's weapons program, has been torn down to its most radioactive portions, sealed up and reroofed to let radiation decay to safer levels over 70 years.

"Washington Closure has done a great job of removing the structures and highly contaminated facilities at the N Reactor area," Rob Cantwell, director of Washington Closure's field remediation program, said in a statement. "Now we begin the final phase of cleaning up the remaining pipelines and soil contamination."

The work is critical to protecting groundwater and the nearby Columbia River, he said.

Terranear will pull out pipes and dig up contaminated soil, and then package material for shipment to the Environmental Restoration Disposal Facility, a lined landfill for low-level radioactive and hazardous chemical waste in central Hanford.

The other eight plutonium-production reactors at Hanford used coal for backup power. But N Reactor, the newest of the nine reactors, used gasoline, oil and diesel instead for backup power.

"The majority of work remaining includes the removal of pipelines and the cleanup of petroleum that was spilled during reactor operations," said Mark Buckmaster, Washington Closure project manager for field remediation at N Reactor, in a statement.

Other piping, including for steam and for sewers, also will be removed.

Terranear is expected to complete work on the three square miles around N Reactor by December 2013. All that should remain is continuing cleanup of groundwater.

Terranear is expected to remove about 275,000 tons of contaminated material. Washington Closure already has removed 875,000 tons of contaminated material, including building rubble, from the N Reactor area.