Full story here on MSNBC.com:
DENVER - More than 1 billion gallons of contaminated water -- enough to fill 1,500 Olympic-sized swimming pools -- is trapped in a tunnel in the mountains above the historic town of Leadville and threatening to blow.
Lake County Commissioners have declared a local state of emergency for fear that this winter's above-average snowpack will melt and cause a catastrophic tidal wave.
The water is backed up in abandoned mine shafts and a 2.1-mile drainage tunnel that is partially collapsed, creating the pooling of water contaminated with heavy metals.
County officials have been nervously monitoring the rising water pressure inside the mine shafts for about two years. An explosion could inundate Leadville and contaminate the Arkansas River.
Lots more info in the link above. Ignoring the catastrophic physical damage such a volume of water could do to a town (and the future shape of the river channel) Heavy metal runoff from mines is one of the most severe forms of pollution. This volume of contaminant could possibly "kill" the Arkansas River. Let's hope they find a way to release the pressure gently and get this taken care of before it's too late.