Hanford Tanks

In this July 9, 2014, photo, a sign informs visitors of prohibited items on the Hanford Nuclear Reservation near Richland, Washington. At least 20 workers were medically evaluated after several of them reported headaches after working near an area where waste from a leaking tank was being transferred, U.S. Energy Department officials said.

(The Associated Press)

RICHLAND, Wash. -- Officials say 20 workers at the Hanford Nuclear Reservation have sought medical attention in the past two days after working near an area where waste from a leaking tank was being transferred.

KVEW-TV reports that 13 of the workers reported having various symptoms after smelling suspicious odors. Officials say seven more sought a medical evaluation as a precaution.

Nineteen of the workers have been cleared to return to work while one was still being evaluated Friday afternoon.

Industrial hygiene workers gathered air samples and analyzed data, which they say found chemical concentrations well below regulatory standards. Chemical vapors are generated in the radioactive and chemical waste stored in the underground tanks.

Earlier this month, officials revealed that a tank known as AY-102 had leaked several thousand gallons of radioactive waste from its primary tank. Last week, officials said they were trying to determine whether a second giant underground tank was also leaking.

The sprawling site near Richland, Washington, was constructed during World War II to make plutonium, a key ingredient in nuclear weapons. Workers at the site are now engaged in cleaning up the leftover waste at a cost of more than $2 billion a year, The Tri-City Herald reported.

The most dangerous wastes are stored in 177 underground tanks, most of them old, single-walled tanks, some of which have leaked. The double-walled tanks were presumed to be much safer.

The latest estimate to finish the cleanup of Hanford is $107.7 billion and the work will take until 2060.

-- The Associated Press