Acid Mine DrainageFor hundreds, if not thousands of years, humans have been extracting metals and stones, and with the advent of more advanced technology and greater needs , the demand for these resources continues to grow. Although these resources benefit our lives in many ways, the effects of mining can be detrimental, and one of these effects is the subject of this essay, acid mine drainage (AMD). The causes of AMD will be discussed, as well as some of the physical and biological problems associated with it. Certain prevention and sanitation treatments will also be considered. Acid mine drainage refers to water (leachate, drainage or seepage) that has come into contact with oxidized rocks or overburden containing sulfides (coal, zinc, copper, lead). (Keller, 2000; USGS; USEPA, 2002). A common sulphide is pyrite, or iron disulphide (FeS2), and throughout this essay it will be pyrite which will be the main sulphide considered. Acid mine drainage is not a new phenomenon; early mining techniques used gravity to prevent water accumulation, leading to water pollution with acid, iron, sulfur, and aluminum (USEPA, 2002). It is most commonly associated with coal mining, particularly soft coal, a coal with a high sulfur content. Pyrite present in coal seams will be accessible after surface mining when the overlying surfaces are removed or in deep mines which will allow oxygen to access the previously inaccessible pyrite-bearing coal (DEP 1 , 1997). Once pyrite is exposed to air and water, sulfuric acid and iron hydroxide form, creating acidic runoff (DEP 1, 1997; 2 2002). When water comes into contact with pyrite, the chemical reactions that take place cause the water's pH to increase which will dissolve the heavy metals that remain in solution. However, when pH levels reach a certain level, iron can then precipitate, coating the sediments with characteristic yellow, red, or orange colorations (DEP 2, 2002; USGS; USEPA, 2002). The rate of progression of AMD is also influenced by the presence of certain bacteria (Doyle; USGS). AMD that has dissolved heavy metals such as copper, lead and mercury can contaminate ground and surface water. Mines located above the water table are particularly threatened (Keller, 2000; DEP 2, 2002). Sources of polluted water can be surface water that seeps into the mine, shallow groundwater that passes through the mine, or any water that comes into contact with tailings produced by the mines..