From what I gathered from the article as well as the one linked to on it. It seems logically natural.
They kept on saying high levels for an "undisturbed area.
Yellowstone is probably one of the MOST disturbed parts of North America. It's constantly volcanic with numerous earthquakes. Not to mention
completely BLOWING UP every 600,000 years or so

.
Seems normal to me.
[Edited on 27-10-2003 by Fry2]