Clean-up depended on the amount of and type of ash on tracks. Washing it down was the method recommended by the Ecology people at the time. The goal was to minimize the contact with it, and to not whip up the lighter ash into the air where people would breath it. Washing down actually worked the best, you can still find the stuff in eastern Washington from time to time---someone will dig a hole and you can see the white layer of the stuff. Ritzville was one of the hardest hit and had to wet down and scoop up the stuff and truck it out of town. They used to have mountains of the stuff piled up north of town. (Most of the ash at Ritzville was a heavier stuff that wasn't easy to deal with.) The weather service was able to track the ash plume all the way around the world at least once. A professor of enviromental science at University of Washington told me just the other day that Mt. St. Helens' blast produced more global warming gases with that one blast (actually small in volcanic terms) than man kind has produced to date. Kinda makes you think with all the volcanos going off (that we know about, not to mention the ones under the ocean) how much of an impact humans really have.