Thanks EPA. Thanks a lot.

http://www.livescience.com/51820-colorado-mine-spill-river-photos.html

Pictures and info about how it occurred and what they are doing to contain the spill.

They don't say how they inadvertently breached the wall to create the spill or if they even knew it was there before it occurred.

Wikipedia has summed it up as well: 2015 Gold King Mine waste water spill

One of the interesting pieces of this story is how the EPA wanted to declare the area a Superfund site years ago so they would have money to clean up the area but the locals were against the Superfund designation.

http://www.livescience.com/51831-colorado-mine-spill-cleanup.html