Mining regulations work to prevent toxic acid drainage.
Mining can also be a destructive force in the environment. Chemical and bacterial reactions in abandoned mines can cause the formation of toxic corrosive acids that work their way into waterways where they can destroy large areas of ecosystems. Since 1978, ecological practices have been initiated to restore mines and mining areas to their original condition. Much work is left to be done.
Acid Drainage
Mining of sulfides, coal, zinc,copper, lead,gold, silver, and uranium causes sulfuric acid to form when the elements are exposed to water, air and some forms of bacteria. The acid dissolves other minerals that are toxic to life and they become part of the drainage. The acid gets into water near mines and lowers the pH, resulting in a corrosive, toxic stew that is unable to support life. When acid drainage spreads, it can destroy large amounts of ground water, making it impotable, useless for consumption and agriculture. Wildlife habitats in areas where water is polluted with acid drainage are diminished or die off completely. Even human-built aqueducts, wells and other structures can become corroded and compromised by water contaminated with acid drainage from mines.
The Scope Of The Problem
Mining regulations are in effect to prevent new sources of acid drainage from mines being worked today. Mining, however, has been going on for hundreds of years in the United States. The Bureau of Land Management estimates there are between 100,000 and 500,000 abandoned mines in the United States. Exact figures are impossible to reach because there are many small mines that are unknown. It is further estimated that between 5 to 10 percent of abandoned mines are environmentally hazardous. While work is ongoing to clean up acid mine drainage, no one solution is applicable to all mines and problems must be solved on a case-by-case basis.
Active Clean-up Techniques
Active cleaning techniques focus on cleaning affected areas and restoring pH balances to water. These techniques require ongoing work as they do not stop the leakage from the source. Wetlands are created and species of waste-eating bacteria are introduced into the areas. Lime is used to neutralize acids and raise pH balance of the water. Using these methods involve continuing efforts which can be hampered by funding and other factors. Active treatments work best when coupled with passive treatments which stem the introduction of acids and metals into the environment.
Passive Clean-up
Passive methods involve stopping drainage at the source. Specially developed grouts are injected into some mine shafts and tunnels to stem the flow of acid drainage. Mine portals can be sealed. "Wet seals" consist of seals with pipes which allow for the collection and treatment of drainage to prevent leakage of the material. Limestone channels, leach beds, and oxic limestone drains are used to neutralize acid before allowing water to escape into the environment. Limestone fills are used to fill in pits which are then restored. Each mine presents it's own obstacles and finding the appropriate solutions is a difficult and expensive undertaking.
