That's according to a new report by the U.S. Department of Energy's Office of Inspector General.
The 1,936 capsules contain radioactive cesium and strontium and are held in giant pools of water on the Hanford site, which is near Richland.
The Tri-City Herald says a severe earthquake could cause a loss of power or water in the storage facility.
The report suggests the capsules should be moved to dry storage as soon as possible.
The capsules, which are about 22 inches long, hold material with 106 million curies of radioactivity, or 32 percent of the total radioactivity at Hanford. The 13 feet of water covering them helps cool the capsules and protects workers from radiation.