Acid mine drainage

Acid mine drainage (AMD) refers to the outflow of acidic water from (usually) abandoned mines. Metal sulfides, often pyrite, newly exposed to air and water are broken down into metal ions and sulfuric acid by colonies of bacteria and archaea. These microbes, called extremophiles for their ability to survive in harsh conditions, occur naturally in the rock, but limited water and air supplies usually keep their numbers low. In some AMD systems temperatures reach 120 degrees Fahrenheit and the pH can be as low as -2.

About half of the coal mine discharges in Pennsylvania are acidic, with pH <5. Generally, limestone or other calcareous strata that could neutralize acid are lacking or deficient at sites that produce acidic mine drainage. Although abandoned underground mines produce most of the AMD, some recently mined and reclaimed surface mines have produced AMD and have degraded local ground-water and surface-water resources. Acidic water produced at active mines must be neutralized to achieve pH 6-9 before discharge from a mine site to a stream is permitted.

See also

• Mining
• Environmental Protection Agency
• Clean Water Act

External links

• Pictures of yellow boy (http://www.mines.edu/fs_home/jhoran/ch126/yellow.htm)
• USGS Mine Drainage (http://geology.er.usgs.gov/eastern/environment/drainage.html)
• Coal-Mine-Drainage Projects in Pennsylvania (http://pa.water.usgs.gov/projects/amd/)
• AMRClearinghouse.org (http://www.amrclearinghouse.org/Sub/AMDbasics/ZZoverview.htm)
• Environmental Mining Council of British Columbia (http://www.miningwatch.org/emcbc/publications/amd_water.htm)

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