The 75-year-old tank, called B-109, at Hanford Nuclear Reservation is estimated to be leaking 3.5 gallons per day, or approximately 1,300 gallons per year of radioactive material. The tank holds around 123,000 gallons of radioactive waste dating back to when atomic bombs were being built throughout the Manhattan Project. 

The Hanford Nuclear Reservation is a decommissioned nuclear production facility operated by the federal government on the Columbia River in Benton County. The facility is about a four-hour drive east of Portland. 

"It's a serious matter whenever a Hanford tank leaks its radioactive and dangerous chemical waste," Ecology Director Laura Watson said.