|Contaminant Issues - Acid Mine
Seepage from an historical
mine tailing deposition areas. Whitewood
Valley, South Dakota. USFWS photo by Joy Gober and Scott Larson.
played an important economic role throughout the history of the United States. After the
precious metals were depleted, many mines were abandoned without any environmental
consideration. Today heavy metals remain in the tailings piles and in the abandoned mines.
Groundwater exiting the abandoned mine portal can eventually enter nearby streams and
contribute high concentrations of heavy metals such as copper, lead, zinc, and mercury.
Precipitation percolating through mine tailings can react with rocks containing sulfur,
leaches out heavy metals and significantly lowers the pH of the water. Water draining from
these tailings piles is referred to as acid mine drainage. The acidity of the water plus
the high metal concentrations can be deadly to animals and plants inhabiting the receiving
streams. Additionally, acid mine drainage coats stream bottoms with iron hydroxide, giving
the subtrates in impacted streams an orange color.
Because acid mine drainage can destroy a stream's aquatic community for miles, many of
the old mining sites are being reclaimed. Reclamation can include plugging old mine addits
and removal, isolation, or burial of tailings piles. Streams are sometimes rerouted to
avoid contact with tailings piles. New technologies include passive treatment systems that
use microscopic organisms to bind metals to a removable substrate.
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