Abandoned mine drainage

Abandoned mine drainage (also known as AMD) is a form of water pollution involving water that has been polluted by contact with mines, typically coal mines. Although it is sometimes called "acid mine drainage", not all abandoned mine drainage is acidic.

The most common form of abandoned mine drainage is acid mine drainage, which is highly acidic water coming from mines. Abandoned mine drainage can become acidic when it is exposed to oxygen and sulfur-containing minerals such as pyrite.

Another form of abandoned mine drainage is alkaline mine drainage. This typically occurs in the presence of minerals such as calcite, limestone, or dolomite. The third form of abandoned mine drainage is metal mine drainage, which occurs when large amounts of metals such as lead contaminate mine water.

The precise chemistry of abandoned mine drainage discharges typically varies. Abandoned mine drainage typically originates in surface mines, deep mines, and "gob piles".

Abandoned mine drainage typically has high concentrations of metals and total dissolved solids.Iron is the most common metal in abandoned mine drainage, but aluminum and manganese occur as well. It may also have a high water temperature and an altered pH, though the characteristics of abandoned mine drainage depend heavily on the area's geochemistry. Other signs of abandoned mine drainage include high sulfate levels and siltation. Acid mine drainage has a pH of less than 7, while alkaline mine drainage has a pH of greater than 7.

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