So, if you don't think the EPA should be cleaning up the mines that leak into Colorado's rivers & public lands, then who do you think should be held responsible to clean it up?

Private companies. That way if something like this happens, then they can be held responsible, and the people who are affected can sue.

How do you think they should clean it up?

For starters, why not remove the water from the top down, instead of blowing a hole toward the bottom of where the contaminated water has collected? This isn't rocket science, it's removing water from somewhere without spilling it. It can be done.

With many of the companies who ran the mines long gone/out of business, where is the funding for them to clean it up going to come from?

From the local governments, of course. You sure as shit don't destroy an area so you can secure funding. What kind of idiot would suggest something like that? Maybe a government worker that's trying to secure funding for his job and can't be punished?

Genuinely curious to hear your solution since you seem to believe there's a legit problem in the government taking the responsibility to clean up contaminated sites.

The problem is you have entities like the EPA that can and WILL destroy local ecosystems to secure funding. If the government paid a private entity to secure the area, then that entity would have incentive not to fuck everything up, since they can be held accountable by market forces. Is this seriously that difficult to comprehend? Incentive always matters. Here we have a perfect example of the government creating its own incentive to destroy people's homes in order to steal more money from the taxpayers so their jobs can be secured. It's predatory, and its despicable, and somehow the government has convinced the lot of you that they are the good guys. I wish I could say I was astonished, but this happens time and time again, and people never seem to get a fucking clue.