> Approximately one month after the spill, the Puerco River had regained normal levels of salinity, acidity, and radioactivity at low flow levels, with contaminants being detectable only after heavy rains.

Natural uranium is mildly radioactive, but it was a uranium mine. The radioactivity was there before they started. They managed to move it around some. The damage was at least as much attributable to the chemical contaminants which would be present in any similar mining incident regardless of what they were mining.

Saying that it was worse than Three Mile Island is a low bar. Three Mile Island wasn't exactly Chernobyl.