I have recently become interested in this...
Last weekend, I was exploring a drainage in the cherokee nf, when I came across a sign in the upper elevations explaining that the stream had been contaminated by acid run-off from iron pyrite, and to be careful when consuming the water.
I was discussing this with Bryce Gibson (some may remember him from the anglers trading co in western plaza in knoxville), and he told me that he remembered a stream near Alum Cave being classified as a dead stream because of a similar sulfate release. He said he thought it had to do with road construction, but he wasn't for sure.
I didn't have my ph meter with me, but next time I go back to the area, I will be sure to take a reading for the upper and lower elevations.
I'd like to do a little more research on the topic...does anyone have any good sites to reference with further information on other streams affected or the amount of water it takes to dilute the acid?