A 25-year project to suck up a cancer-causing chemical from the soil in central Hanford has ended in success.
“It’s one of the longest running cleanup projects on the Hanford Site,” said Karen Wiemelt, vice president of soil and groundwater cleanup for Hanford contractor CH2M Hill Plateau Remediation Co.
Nearly 90 tons of carbon tetrachloride were removed from soil as deep as 200 feet below the ground in central Hanford.
The chemical was used in the process to recover plutonium from liquid waste at the Plutonium Finishing Plant from 1955-73, according to DOE. Carbon tetrachloride is more commonly known for its past use as a dry cleaning solvent.
Over the years at Hanford, hundreds of thousands of gallons of the solvent were discharged into the soil near the Plutonium Finishing Plant.
They left three-quarters of a square mile of soil contaminated, with some of it reaching the groundwater more than 200 feet below the ground’s surface. There, it spread to contaminate abut 5 square miles of groundwater.
The 200 West Pump and Treat Facility that opened in 2012 is removing carbon tetrachloride, among other chemicals from contaminated groundwater, and then reinjecting clean water back into the ground.
Removing the carbon tetrachloride from the soil prevented more of it from reaching the groundwater, which helps protect the Columbia River, Wiemelt said. Groundwater in central Hanford moves toward the river.
Hanford officials turned to technology already used in the petroleum industry, soil vapor extraction, to clean the soil. Similar systems have been used to remove gasoline from the soil surrounding leaking underground storage tanks at gas stations.
But as the technology was investigated for Hanford use in the early 1990s, it had never been used on such a large project, Hanford officials said at the time.
At Hanford, a large vacuum pump was attached to monitoring wells near the Plutonium Finishing Plant.
The vacuum created an air flow in the soil, causing the heavy liquid to evaporate and the vapor to be drawn through the soil and into a well with openings along its sides.
As it went up the well, it was collected on activated carbon. In recent years the contaminated filters have been disposed of at a lined landfill in central Hanford.
About 60 percent to 70 percent of the carbon tetrachloride removed was collected in the first five years of operating the extraction system, Wiemelt said. Results were best in hot weather when carbon tetrachloride most easily converted to a vapor.
The system was shut down periodically in later years of the project to see if residual contamination would return.
The final shutdown was in 2012, when carbon tetrachloride was in concentrations too low for the system to be effective and appeared to meet legal cleanup standards.
But DOE and contractors continued to monitor the soil for the next several years, proving to the Environmental Protection Agency, the regulator on the project, that the chemical was removed from the entire area.
Total project costs were not immediately available, but from 2002-15 about $9.6 million was spent, a relative bargain at a site that spends more than $2 billion a year on cleanup.
“EPA was very pleased with how effective this early action was in addressing contamination,” said Emerald Laija, an EPA environmental scientist.
The project, which required persistence by workers, has been another important step in protecting Hanford groundwater and the Columbia River, said Michael Cline, director of the Department of Energy soil and groundwater division at Hanford.