Acid Mine DrainageFor hundreds, even thousands of years, humans have mined metals and stones, and with the advent of more advanced technology and greater needs, the demand for these resources continues to grow. While these resources benefit our lives in many ways, the effects of mining can be harmful, and one such effect is the topic of this essay, acid mine drainage (AMD). The causes of AMD will be discussed, along with some of the physical and biological problems associated with it. Some prevention and remediation treatments will also be taken into consideration. Acid mine drainage refers to water (leachate, drainage or seepage) that has come into contact with oxidized rock or overburden containing sulfurous material (coal, zinc, copper, lead). (Keller, 2000; USGS; USEPA, 2002). A common sulfide is pyrite, or iron disulfide (FeS2), and pyrite will be the primary sulfide considered in this essay. Acid mine drainage is not a new phenomenon, early mining techniques used gravity to avoid water stagnation, resulting in water pollution from acid, iron, sulfur and aluminum (USEPA, 2002). It is most commonly associated with coal mining, particularly soft coal, coal that has a high sulfur content. Pyrite present in coal seams will be accessible after surface mining when overlying surfaces are removed or in deep mines that allow oxygen access to previously inaccessible pyrite-bearing coal (DEP 1, 1997). After pyrite is exposed to air and water, sulfuric acid and iron hydroxide are formed, creating acidic runoff (DEP 1, 1997; 2 2002). When water comes into contact with pyrite, the chemical reactions that take place cause the water to raise the pH which will dissolve the heavy metals that remain in solution. However, when pH levels reach a certain level, iron can precipitate, coating sediments with characteristic yellow, red, or orange colors (DEP 2, 2002; USGS; USEPA, 2002). The rate at which AMD progresses 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 at risk (Keller, 2000; DEP 2, 2002). Water sources that become polluted can be surface water that permeates into the mine, shallow groundwater that flows through the mine, or any water that comes into contact with waste produced by the mines.