Two Richland businesses have been picked to dig a hole the size of 15 football fields and 85 feet deep at Hanford.
Sage Tec, which teamed with Federal Engineers and Constructors, won the Washington Closure Hanford subcontract to dig the hole and remove soil contaminated with chromium near Hanford's C Reactor.
The subcontract is worth up to $5.3 million.
Soil usually is dug up to about 15 feet deep and occasionally as deep as about 35 feet in the area along the Columbia River at Hanford to remove contamination, said Washington Closure spokesman Todd Nelson.
"We consulted with mining engineers to ensure that we could safely excavate a hole 85 feet deep and get equipment into and out of it," said Dean Strom, the Washington Closure project manager overseeing the work.
Sides of the hole will have to be sloped and roads will have to be built to allow equipment to be driven to the bottom.
Washington Closure expects that 500,000 tons of contaminated soil will be dug up and taken to the Environmental Restoration Disposal Facility, a lined landfill in central Hanford.
To keep up with work across the Hanford site, an expansion has been under way since near the first of the year to add two super-sized disposal cells to increase the ERDF landfill's capacity by 50 percent.
Soil just from the waste site near C Reactor will fill about 18 percent of one of the new super cells.
Some of the soil might have enough contamination that it will need to be treated by mixing it with grout before it will be accepted for disposal.
A large amount of clean soil also is expected to have to be removed to reach the contaminated soil.
"What makes this cleanup project more challenging than previous waste site cleanup efforts is the depth workers may have to dig and the amount of clean soil that will need to be removed to get to the chromium source and remove the contaminated soil," Strom said.
Chromium was added to water in Hanford reactors, including C Reactor, to prevent corrosion when the reactors were operated to produce plutonium during World War II and the Cold War.
C Reactor operated from 1952-69. The contamination near C Reactor is believed to have come from a leaky pipe and from a spigot on a tank that was left open through a weekend in the early '60s, Nelson said.
The waste site is less than a mile from the Columbia River, posing a threat of more chromium reaching the ground water and then the river. The chemical is toxic to young salmon.
Excavation is expected to begin in January and take about six months to complete.
Load out, transportation and disposal in the central Hanford landfill should begin in February and take about one year. Another subcontract will be awarded to backfill the hole.
w Annette Cary: 582-1533; email@example.com; More Hanford news at hanfordnews.com.