Treatment systems at Hanford have removed more than 680 pounds of the contaminant hexavalent chromium from groundwater near the Columbia River so far this fiscal year.
The Department of Energy's goal was to remove about 550 pounds by the end of the fiscal year Sept. 30, an objective that DOE and its contractor CH2M Hill Plateau Remediation Co. met four months early.
In fiscal 2012, more than 1,000 pounds of chromium were removed from near the river at Hanford, and in fiscal 2013, about 871 pounds of chromium were removed, beating a goal set that year of 500 pounds of chromium.
Goals are set that are lower than previous years' work because as the concentration of chromium in the plumes near the rivers decreases, it takes more effort to remove the same amount of chromium from the groundwater.
The primary concern about chromium-contaminated groundwater near the Columbia River is risk to aquatic species that live among the gravel below the water where Hanford groundwater enters the river and are particularly sensitive to chromium. They require stricter standards than those set to protect people from chromium, which can cause cancer.
Hexavalent chromium that weighs as little as a grain of sand can contaminate eight gallons of water above aquatic standards, according to CH2M Hill.
Concentrations of the chromium in the groundwater have gone down because of work to treat groundwater and an aggressive effort to dig up contaminated soil that was providing a source of pollution for the groundwater.
The largest source of chromium contamination near the Columbia River at Hanford has been removed after workers dug up contaminated soil down to groundwater 85 feet deep in the area near the former D and DR reactors along the Columbia River.
Chromium was used as a corrosion inhibitor added to the river water used to cool Hanford reactors when the reactors were producing plutonium. Some of the chromium spilled or leaked from pipes.
"Our contractor removed more chromium than forecasted this year by pulling more groundwater from the areas of highest contamination," said Briant Charboneau, director of DOE's Hanford soil and groundwater division.
New wells were added and moved to the places where contamination was high, said Jim Hanson, the DOE project lead for groundwater contamination at the K East, K West, D, DR and H Reactor areas.
Hanford has five pump and treat systems for chromium contamination near those reactors. They pump up contaminated water, clean it and then inject it back into the ground to help drive contaminated groundwater toward the extraction wells.
CH2M Hill also has improved the performance of the pump and treat systems, in no small part because of input from its operations, maintenance and engineering staff, said Bill Barrett, CH2M Hill director of operations for soil and groundwater cleanup.
DOE added two new pump and treat systems in 2010 and 2011 that use a resin to strip chromium out of the water. The resin needs to be replaced less often than the resin previously used at Hanford, which has reduced down time. The three older systems also have been switched to the new resin.
That has allowed modifications in how the older plants are run, allowing one of them to operate at 150 percent of its design, Barrett said.
The newer plants also have had minor modifications to allow the amount of water run through them for treatment to be increased, he said.
DOE and Hanford contractors have removed almost 3 tons of chromium from groundwater since treatment systems began operating in the mid-'90s.