Acid mine drainage
Acid mine drainage (AMD) refers to the flow of acidified waters resulting from mining operations and the waste they generate, leading to significant environmental pollution. This process occurs when minerals, particularly pyrite (iron sulfide), are exposed during mining activities. Rainwater or surface water interacts with these minerals, resulting in the formation of sulfuric acid, which can leach into nearby groundwater and surface water bodies, causing widespread contamination. The acidic waters dissolve heavy metals and other toxic substances, such as lead and arsenic, further degrading water quality and harming aquatic ecosystems.
AMD is particularly concerning as it affects not only the immediate environment around mining sites but can also impact distant water bodies, leading to ecological devastation. The consequences include the loss of biodiversity, changes in nutrient cycling, and severe toxicity for water-dwelling organisms, such as fish and plankton. Additionally, human health risks arise from contaminated drinking water sources, with some individuals experiencing serious health issues, including skin cancer from arsenic exposure. Major sites of AMD pollution, such as Tar Creek in Oklahoma and the Butte and Anaconda areas in Montana, highlight the extensive damage caused by this phenomenon, prompting significant governmental cleanup efforts. Understanding AMD is crucial for environmental protection and the sustainable management of mining activities.
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Acid mine drainage
DEFINITION: The flow of acidified waters from mining operations and mine wastes
Acid mine drainage can pollute groundwater, surface water, and soils, producing adverse effects on plants and animals.
During mining, rock is broken and crushed, exposing fresh rock surfaces and minerals. Pyrite, or iron sulfide, is a common mineral encountered in metallic ore deposits. Rainwater, groundwater, or surface water that runs over the pyrite leaches out sulfur, which reacts with the water and oxygen to form sulfuric acid. In addition, if pyrite is present in the mining waste materials that are discarded at a mine site, some species of bacteria can directly oxidize the sulfur in the waste rock and tailings, forming sulfuric acid. In either case, the resulting sulfuric acid may run into groundwater and streams downhill from the mine or mine tailings.
Acid mine drainage (AMD) pollutes groundwater and adjacent streams and may eventually seep into other streams, lakes, and reservoirs to pollute the surface water. Groundwater problems are particularly troublesome because the of polluted groundwater is very difficult and expensive. Furthermore, AMD dissolves other minerals and heavy metals from surrounding rocks, producing lead, arsenic, mercury, and cyanide, which further degrade the water quality. Through this process, AMD has contributed to the pollution of many lakes.
AMD can be devastating to the surrounding ecosystem. Physical changes and damage to the land, soil, and water from AMD directly and indirectly affect the biological environment. Mine water immediately adjacent to mines that are rich in sulfide minerals may be as much as 100,000 to 1,000,000 times more acidic than normal stream water. AMD water poisons and leaches nutrients from the soil so that few, if any, plants can survive. Animals that eat those plants, as well as microorganisms in the leached soils, may also die. AMD is also lethal for many water-dwelling animals, including plankton, fish, and snails. Furthermore, people can be poisoned by drinking water that has been contaminated with heavy metals produced by AMD, and some people have developed skin cancer as a result of drinking groundwater contaminated with arsenic generated by AMD leaching.
Alterations in groundwater and surface-water availability and quality caused by AMD have also had indirect impacts on the environment by causing changes in nutrient cycling, total biomass, species diversity, and ecosystem stability. Additionally, the deposition of iron as a slimy orange precipitate produces an unsightly coating on rocks and shorelines.
AMD was so severe in the Tar Creek area of Oklahoma that the US Environmental Protection Agency designated the area as the nation’s foremost hazardous waste site in 1982. The largest complex of sites in the United States was produced by the mines and smelters in Butte and Anaconda, Montana, with much of the pollution attributed to direct and indirect effects of AMD. AMD is also a widespread problem in many fields in the eastern United States. In 2013, Earthworks, a nonprofit environmental organization, issued a report, based on its review of extensive government documents, revealing the size and scope of the problems created because of AMD. The forty hard-rock mines studied are projected to contaminate between 17 and 27 billion gallons of water. The Environmental Protection Agency (EPA) has spent more than $210 billion cleaning up the damage caused by acid runoff from the Summitville Mine, Colorado, alone.
Bibliography
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Gestring, Bonnie, and Lisa Sumi. “Polluting the Future: How Mining Companies Are Polluting Our Nation’s Waters in Perpetuity. Earthworks. Earthworks, 1 May 2013. PDF file.
"How Does Mine Drainage Occur?" U.S. Geological Survey, www.usgs.gov/faqs/how-does-mine-drainage-occur. Accessed 15 July 2024.
Jacobs, James A., Jay H. Lehr, and Stephen M. Testa. Acid Mine Drainage, Rock Drainage, and Acid Sulfate Soils: Causes, Assessment, Prediction, Prevention, and Remediation. Hoboken: Wiley, 2014. Print.
“Watershed Contamination from Hard Rock Mining.” USGS. United States Geological Survey, 6 May 2014. Web. 29 Jan. 2015.
Younger, Paul L., Steven A. Banwart, and Robert S. Hedin. Mine Water: Hydrology, Pollution, Remediation. Norwell: Kluwer Academic, 2002. Print.