Hanford officials say unusual radiation readings that led them to declare an emergency operations alert last month came from old contamination.
Hanford officials told the Tri-City Herald they found no evidence of a new leak from a waste removal system or its transfer hoses.
They told employees on Tuesday that an investigation found insulating blankets that had been used to shield radiation on a small area had shifted. That caused radiation readings to go up during routine monitoring.
Because the abnormal reading could have been caused by a leak, workers at the C Tank Farm were evacuated overnight on Aug. 21 and workers in central Hanford and near the K Reactors were ordered to take cover indoors.
Before work restarts this week, the hot spot will be recovered.