The Office of Special Reclamation is required to treat polluted mine drainage from mine sites that have had their mining permits revoked and bonds forfeited. Polluted mine drainage may be
acidic with pH values less than the lower acceptable limit for water quality standards (< 6 on a standard pH scale) and high metal content, primarily iron, aluminum, and manganese, or
alkaline with a higher pH (>6) and high metal content, usually iron.
Acid mine drainage, generally referred to as AMD, requires alkaline addition to raise the pH. Alkalinity is generally in the form of lime products such as limestone or
hydrated lime, or other products such as sodium hydroxide, calcium hydroxide, or anhydrous ammonia.
Alkaline mine drainage, on the other hand, does not require any pH adjustments. This type of mine drainage is generally treated passively which requires ample space for
treatment. If ample space is not available, alkaline mine drainage may require chemical addition in the form of oxidizers, coagulants, or polymers which enhance the
settling of metal particulates resulting in clearer water.