Acid mine drainage is considered one of mining’s most serious threats to water resources. A mine draining acid can devastate rivers, streams, and aquatic life for hundreds, and under the “right” conditions, thousands of years.
How does Acid Mine Drainage take form?
In hard rock mines, the target ore (like nickel, copper, platinum, etc) is often rich in sulfide minerals. When the mining process exposes the sulfides to water and air, together they react to form sulfuric acid. This acid can dissolve other harmful metals and metalloids (like arsenic) from the surrounding rock. Acid mine drainage can be released anywhere on the mine where sulfides are exposed to air and water — including waste rock piles, tailings, open pits, underground tunnels, and leach pads.
Acid mine drainage can have severe impacts on fish, animals and plants. Many impacted streams have a pH of 4 or lower — similar to battery acid.
Acid mine drainage is especially harmful because it can occur indefinitely — long after mining has ended. A literature review on acid mine drainage concluded that “no hard rock surface mines exist today that can demonstrate that acid mine drainage can be stopped once it occurs on a large scale.”
Throusands of old mines sites or old mining tailings across North America may require water treatment for hundreds to thousands of years, or “in perpetuity” as a result of acid mine drainage or metals leaching.
Water treatment can be a significant economic burden to the public if a company files for bankruptcy or refuses to cover water treatment costs.
For example, acid runoff from the Summitville Mine in Colorado killed all biological life in a 17-mile stretch of the Alamosa River. The site was designated a federal Superfund site, and the EPA has spent over $210 million on clean-up.