Acid mine drainage

Toxic metal mine tailings
Acid leaching from mining residues
Worldwide, acid mine drainage is considered the most serious environmental problem in the mining sector. Acid mine drainage occurs when the sulphides contained in mine tailings are exposed to oxygen and water to become sulphuric acid. The result pollutes the watershed causing considerable damage to the environment and imposing expensive solutions on mining companies as well as governments.
Mining produces 15 billion tonnes of residues each year, adding to the material produced for hundreds of years.
Aggravated by 
(G) Very specific problems