Anne Smith, a spokeswoman for URS-CH2M Oak Ridge, said the contractor recently completed its 18th shipment of radioactive sludge — totaling 90,000 gallons — to a treatment facility in Washington state.
Sludge has been removed periodically from the Rarity Ridge Wastewater Treatment Plant to help reduce the levels of radioactive technetium-99, which infiltrated pipelines leading to the sewage plant during demolition activities at the former K-25 uranium-enrichment facility.
The technetium in the sewer system was discovered in early 2014, prompting a number of actions — although officials have said the radioactivity doesn’t pose a threat to workers at the sewage-treatment plant and hasn’t been elevated in discharges to the Clinch River.
Levels of technetium-99 in the sewage plant’s “sludge digester” have dropped from 904,000 picocuries per liter in April 2014 to 91,100 picocuries per liter in March 2016, Smith said.
A picocurie is one-trillionth of a curie, a standard measure of the intensity of radioactivity in a sample of radioactive material.
The UCOR spokeswoman said it would “speculative” to estimate how many more shipments of sludge will be needed to complete the cleanup effort and bring radioactivity levels back to normal at the city’s plant.
A return to “normal” levels will be a “collaborative decision” based on an evaluation of numerous factors related to the technetium levels, she said via email.
The sludge removed from the Oak Ridge sewage-treatment plant is shipped to a Perma-Fix waste-treatment facility in Richland, Wash. The residual material after thermal treatment is sent to a landfill in Utah for disposal.
Oak Ridge City Manager Mark Watson said there has been notable progress in the cleanup effort.
“I think the technetium has steadily gone down once that awareness came about,” he said. “They estimate that to be about a three-year cycle (to complete the cleanup).”
Watson said the project seems to be “moving along,” with the radioactive contamination continuing to decline.
He said he expects the city and DOE will sit down at some point and discuss the conclusion of the project.
A feature on Atomic City Underground allows readers to sign up for email updates and receive a notice each time new information is posted. Just put your email address in the box on the lower right of the blog’s front page and follow instructions. Thanks to all loyal readers.