Acid mine drainage
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Acid mine drainage is water containing sulfur-bearing minerals produced from mining activities. The drainage is formed by a chemical reaction between water and rocks containing pyrite, a sulfur-bearing mineral in rocks exposed during ore or coal mining. The water is typically acidic because water flowing through or over sulfur-bearing minerals react to produce acidic aqueous solutions.[1][2]
Acid mine drainage is considered nonpoint source pollution, which is pollution from several separated sources, such as precipitation, atmospheric deposition, and land runoff. As such, the drainage is regulated by the federal government through mine site cleanup projects. In addition, mining operators adopt treatment measures to reduce the acidity of drainage water.[3]
Background
Rocks containing pyrite, an iron sulfide, are sometimes exposed to air during ore or coal mining, which increases the exposed surface area of sulfur-bearing rocks. The exposed pyrite reacts with water and oxygen to produce dissolved iron and sulfuric acid. The iron then forms yellow, red, or orange sediments in water in mine drainage (the outflow of water from metal or coal mines). The drainage can make its way from underground mines to surface water or groundwater. This occurs mainly in mines that were improperly restored to pre-mining conditions. The most common environmental effects of acid mine drainage are water contamination, infrastructure corrosion, and disruption of aquatic life, such as fish.[4][5]
Measuring for drainage
Private companies and government agencies attempt to predict the amount of acidic drainage in a proposed mine site. Though uncertainty exists on the precise amount of drainage in a mine given the variables involved in drainage generation and the continuing refinement of measurements, scientists can detect the quantity and presence of acid-forming and acid-neutralizing minerals within the geological formations to be mined. This involves drilling to collect samples for analysis about the amount of sulfur present and the potential for acid formation. The amount of acid-forming minerals can be contrasted with the amount of acid-neutralizing minerals to determine which geologic materials are more likely to generate acidic drainage during mining.[5]
Treatment
Treating acid mine drainage take two forms: active and passive. Active treatments include reducing the acidity of the drainage from inside the mine itself. These treatments include chemically neutralizing the water's acidity with a neutralizing agent, such as limestone, soda ash, ammonia, and hydrated lime. Some mines contain ponds used to remove iron, manganese, and other chemicals from the drainage before it is discharged through a pumping system. Given generally high capital and operational costs each year and the constant supervision required for active treatments, many sites adopt passive treatment measures.[6][7][8]
Passive treatment systems use biological and chemical processes to decrease metal concentrations and thus the acidity of mine drainage. The most common passive technologies are aerobic wetlands, limestone drains, and reducing and alkalinity-producing systems (RAPS). Aerobic wetlands are used to treat less acidic mine water while limestone drains are used to treat more acidic water. RAPS are used to direct water flow through organic materials and into limestone. This results in sulfate reduction and hence greater alkalinity (alkalinity refers to the capacity of an aqueous solution to neutralize acids.[9]
Regulation
Federal reclamation program
In 1977, Congress enacted the Surface Mining Control and Reclamation Act, which established the federal Abandoned Mine Land Reclamation Program. The program focuses on restoring abandoned or insufficiently reclaimed mine land affected by coal mining operations. Reclamation projects are designed to treat polluted surface water and groundwater, close entrances to underground mines, drain water-filled pits, remove sediments from streams, limit damage from landslides, and more. Under the program, states and American Indian tribes can develop reclamation plans, which may be submitted to the federal government to gain federal funding for state or tribe-designed reclamation projects.[10]
Superfund
In 1980, Congress passed the Comprehensive Environmental Response, Compensation and Liability Act, which gave the U.S. Environmental Protection Agency (EPA) power to regulate hazardous substances at contaminated waste sites, including abandoned mines, nationwide. The act also permitted the EPA to judge individuals or companies liable for contamination and force these parties to pay for site cleanup. CERCLA imposes a fine of $25,000 per day for failure to comply with any CERCLA order. If the EPA makes an agreement with responsible parties cleanup work, the agency may also apply penalties if the responsible party does not adhere to the agreement's requirements.[11][12]
The act also established the Superfund program, a federal system listing contaminated sites listed by priority and level of waste contamination. The Superfund program is also known as the National Priorities List. The EPA is required to update the National Priorities List once every year, and sites near the top of the list receive the most attention. Once Superfund was established, the EPA and state agencies began adding some abandoned mines as cleanup sites. As of April 2016, there were 113 proposed and officially listed abandoned mines on the National Priorities List of Superfund sites.[13][11][12]
See also
Footnotes
- ↑ Reclamation Research Group, "Acid Mine Drainage and Effects on Fish Health and Ecology: A Review," June 2008
- ↑ U.S. Environmental Protection Agency, "What is Acid Mine Drainage," accessed May 15, 2016
- ↑ U.S. Environmental Protection Agency, "Abandoned mine drainage," accessed December 22, 2016
- ↑ Trout Unlimited, "Abandoned Mine Drainage," accessed December 22, 2016
- ↑ 5.0 5.1 U.S. Fish and Wildlife Service, "Acid Mine Drainage and Effects on Fish Health and Ecology: A Review," June 2008
- ↑ Lehigh University, "Active treatment of Acid Mine Drainage: techniques and costs," accessed December 22, 2016
- ↑ Science Learn, "Treatments for acid mine drainage," accessed December 22, 2016
- ↑ Australian Centre for Minerals Extension and Research, "A Summary of Passive and Active Treatment Technologies for Acid and Metalliferous Drainage (AMD)," accessed December 22, 2016
- ↑ U.S. Department of Energy, "The Passive Treatment of Coal Mine Drainage," accessed December 22, 2016
- ↑ Federal Register, "Abandoned Mine Land Reclamation Program; Limited Liability for Noncoal Reclamation by Certified States and Indian Tribes," February 5, 2015
- ↑ 11.0 11.1 U.S. Environmental Protection Agency, "Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)," accessed February 17, 2015
- ↑ 12.0 12.1 Congressional Research Service, "Comprehensive Environmental Response, Compensation, and Liability Act: A Summary of Superfund Cleanup Authorities and Related Provisions of the Act," June 14, 2012
- ↑ U.S. Environmental Protection Agency, "Abandoned Mine Lands: Site Information," accessed December 22, 2016
