AIKEN, S.C. – The Savannah River Site (SRS) has made significant progress in cleaning up contaminated groundwater from legacy nuclear operations near two chemical separations facilities.
F Canyon closed after its mission was completed in 2002, and H Canyon is still active. For decades, operations in both canyons generated low-level radioactive waste solutions that were disposed in pond-like pools of water known as seepage basins. Although the last of those basins was backfilled, capped, and closed in 1991, 33 years of use had resulted in contamination of groundwater beneath each basin.
SRS employs a phased groundwater cleanup approach with innovative remedial technologies. They include underground barrier walls that redirect and channel groundwater flow toward base injection zones that make the groundwater less acidic and reduce the migration of contaminants.
“The groundwater under the basins is acidic from nitric acid present in the waste solutions,” said Jeffrey Thibault, engineering and remediation support for SRS management and operations contractor Savannah River Nuclear Solutions (SRNS). “The acidic property of the water allows some contaminants to remain dissolved and slowly migrate with the groundwater. Our system uses a wall to direct the water into open spaces, called gates, where a base solution is injected into the water to increase the pH and slow down the movement of the contaminants.”
Installed in 2004, this system marked a shift towards a more passive, cost-effective system that provided improved remedial effectiveness without creating radioactive waste that had to be managed and disposed. Previously, EM had built two water treatment units to clean the contaminated groundwater, extracting and treating it before injecting the cleaned water back into the ground. But this method was costly, and it produced radioactive waste sludge that was expensive to dispose.
The environmentally harmless base solution in the current system includes clean water from the site’s drinking water system and baking soda. A system of pumps, sensors, and piping, mounted on a small metal skid platform, blends the mixture with more water in precise proportions prior to delivering the solution through underground pipes to a network of 24 injection wells near F Canyon. A similar system is located near H Canyon.
The wells are turned on when treatment is needed to neutralize the acidic water. Once enough of the solution has been injected, the wells are turned off for a period of 12 to 18 months, until sampling data shows treatment is required again.
Since SRNS became the SRS management and operations contractor in 2008, 126.4 million gallons of base solution have been injected into the groundwater near F Canyon and 46.3 million gallons have been added near H Canyon.
Thibault noted that the passive remedial system is economically and environmentally friendly, restoring the pH of the groundwater to more natural conditions and letting nature essentially take care of itself.
“We’ve seen great results from this method,” Thibault said. “It’s effectively a passive system, meaning we only run it every few months, when testing shows that the acidity is increasing in the soil again,” he said. “Restoring the neutral pH of groundwater at F and H areas reduces the migration of hazardous and radioactive metal contaminants in the groundwater and acts to protect a nearby stream.”
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