“Until a few years ago, we were discussing whether it would happen at all, as a kind of low-probability, high-impact risk,” Rahmstorf told CNN. “And now it looks a lot more likely than just a few years ago that this will happen. Now people are starting to close in on when it will happen.”
Its not fallout, but groundwater contamination from poorly stored and buried, leaking nuclear waste, left over from the Hanford plant that produced much of the fissile material for the Manhattan Project and another decade or two of the early US nuclear weapons industry.
To the best of my knowledge, Eastern WA was never had a test area for actual nuclear explosions producing fallout.