USGS Frequently Asked Questions
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Question:
How does mine drainage occur?
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Answer: Mine drainage is formed when pyrite, an iron sulfide, is exposed and reacts with air and water to form sulfuric acid and dissolved iron. Some or all of this iron can precipitate to form the red, orange, or yellow sediments in the bottom of streams containing mine drainage. The acid runoff further dissolves heavy metals such as copper, lead, mercury into ground or surface water. The rate and degree by which acid-mine drainage proceeds can be increased by the action of certain bacteria.
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Source of this FAQ:
http://geology.er.usgs.gov/eastern/environment/drainage.html
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U.S. Department of the Interior |
U.S. Geological Survey