HANFORD — The Department of Energy is preparing to build Hanford’s largest water treatment system to clean up one of Hanford’s most problematic underground plumes of contaminated water.
It has signed a record of decision with it regulators, the Environmental Protection Agency and the Washington State Department of Ecology, committing to the cleanup work, DOE announced Thursday.
“Pulling this contaminated water out of the ground and treating it is critical to preventing contamination in Hanford’s central plateau from traveling toward the Columbia River,” Dave Brockman, manager of DOE’s Hanford Richland Operations Office, said in a statement.
Underneath most of the 200 West Area in central Hanford lies a 5-square-mile plume of ground water contaminated with carbon tetrachloride. Contamination from the chemical used as a solvent in plutonium processing facilities has been measured in concentrations as high as 1,000 times the amount allowed in drinking water.
In addition portions of the ground water beneath the 200 West Area also are contaminated with trichloroethylene, chromium, nitrate and radioactive technetium 99, iodine 129 and tritium.
DOE is planning to build Hanford’s largest pump and treat station at a cost of $174 million to attack the contaminants and clean the water.
The system will require drilling more than 50 wells to pump contaminated water out of the ground or return cleaned water to the ground. The new system, with multiple treatment units, will have a throughput of more than 1,600 gallons per minute. The cleaned water then can be returned to the ground.
Work on designing the new system has started, and initial estimates call for bringing the system online in two to three years.
It will replace a smaller treatment system installed in the 1990s as a stop-gap measure to prevent carbon tetrachloride from spreading. The smaller system has treated about 1 million gallons of ground water, removing about 12 tons of carbon tetrachloride.
The new system is expected to remove 95 percent of the contaminants in the plume beneath the 200 West Area within 25 years. The remaining contaminants are expected to naturally reduce over the next 100 years.
“This does represent a commitment to a long-term problem at Hanford,” said Dave Einan, EPA environmental engineer. “We’re glad to see it.”
Most of the contamination in the 200 West Area ground water is from liquid waste from processing plants, such as T Plant and the Plutonium Finishing Plant, which produced plutonium for the nation’s nuclear weapons program. The waste was poured into the soil in disposal cribs from 1945 to the early 1970s, and the more mobile contaminants reached the ground water.
An estimated 800 to 1,000 tons of carbon tetrachloride were included in the discharges, making the contaminated ground water beneath the 200 West Area, officially called the 200-ZP-1 operable unit, one of DOE’s most problematic plumes.
The plume is large and the concentration is high. But in addition, carbon tetrachloride adds complexity to the cleanup because it is heavier than water, Einan said. While some contaminants stay within the upper inches of an underground aquifer, carbon tetrachloride tends to sink, according to DOE.
“So not only is it 5 miles wide, it is also a deep contaminant,” said Geoff Tyree, DOE spokesman. “It is more difficult to go deeper into the ground water for this contaminant.”