RICHLAND, Wash. -

A Hanford contractor has identified two possible sources of fumes that have sickened 18 workers over the past two weeks at tank farms holding radioactive and chemical wastes.

The contractor, Washington River Protection Solutions, said Thursday an investigation found a cut in insulation at a pump and liquid in unused equipment.

The Tri-City Herald reports the cut has been sealed and the old equipment has been cordoned off.

All the workers who reported symptoms have been cleared to return to work, including four who were sent to Kadlec Regional Medical Center in Richland.

The symptoms include sore throats, headaches, coughing, burning eyes, nose bleeds, a metallic taste, dizziness and an accelerated heart rate.

Hanford tanks hold 56 million gallons of waste from nuclear weapons production.