Mining debris = Rocks and earth.
Ever been around actual mines and seen how they operate? I have, and it ain't just "rocks and earth" that is the debris. Some mining operations use various chemicals in their operations. Remember the old mines that put all that toxic fluid in the CO river last year?
And, even if it is just "rocks and earth", it can have a serious impact on the surrounding area, because they pile up LOTS of rocks and nothing grows around the piles that they leave. Saw that in the abandoned gold mines in CO and MT, because my foster father was a geologist and dragged the family around to some of those sites to see if there was any gold left.
Oh, yeah. My Grandfather was a Pennsylvania coal miner...a true subterranean shaft miner. My cousin is a West Virginia coal mine engineer at a mostly surface strip-mining operation. THIS is the coal mining operation that the ascribed regulations was designed to shut down...because all that rock and earth that was moved ended up in the valleys, and invariably in those valleys there was some type of water flow that was buried. The streams were either subsumed, creating a spring, or redirected.
This is not about clean water...the water itself is just as clean as it was when it flowed over other dirt and rocks. It can disturb the flow, and even change the course of small seasonal stream beds...but a natural event like a rock slide caused by seismic tremors or erosion could do the same. And I agree that this should be discouraged as much as possible.
But an outright ban based on BS claim of clean water...it was nothing more than environmental overreach masquerading under the cover of a false emotional argument, IMO.
As to gold mines in Colorado, I've been into the working Gold Mine at Cripple Creek. The security is, as you'd imagine, pretty intense. The ore was outside in huge, shallow, plastic lined depressions, soaking in a water based cyanide solution. The cyanide solution leached the gold and other metals from low grade ore. Now there is some mine debris I wouldn't want in my water supply.
Google Maps
The black is the plastic liner, and you can see all the areas covered by ore. That little red dot is a Chevy 3500 or F-350 Super Duty...for comparison sake.
P.S. - If you get a chance to go to Cripple Creek, don't pass it up...it is truly a beautiful mining town.