OAK RIDGE, Tenn. (AP) — A U.S. Department of Energy contractor says radioactivity levels have dropped at an Oak Ridge sewage treatment plant in the past two years.

The Knoxville News Sentinel (http://bit.ly/1TSyxgy ) says levels of radioactivity at Rarity Ridge Wastewater Treatment Plant have fallen by 90 percent as 90,000 gallons of radioactive sludge were removed to a treatment facility in Washington state.

Spokeswoman Anne Smith of URS-CH2M Oak Ridge says the contractor recently completed its 18th shipment of radioactive sludge to the Washington state facility.

Radioactive technetium-99 inflitrated 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. Officials have said the radioactivity doesn't pose a threat to workers at the sewage treatment plant.