Run-off from mines and stockpiles pose a threat to drinking water sources due to the release of salts, metals, and acid drainage. Removal of salts and metals from water resources is difficult and very costly. Metals may adhere to soil particles, making them virtually impossible to remove.
Coal and metal strip mines are a source of water contamination due to the release of metals and acid. Sulfuric acid is formed when sulfides, such as pyrite are exposed to air and water. This is called acid mine drainage. As the sulfuric acid percolates through surrounding rock, metals are dissolved and released into the water stream. Gold, copper, and uranium mines can pose a serious threat to surface and groundwater with the release of toxic metals, such as copper, and radioisotopes. Reclamation of these waters are a serious challenge. Some mines produce such large flows of acidic metallic water that they have been designated by the Environmental Protection Agency (EPA) as Superfund sites.
Rural water supplies in the vicinities of mines may be at risk for contamination. Public water supplies are monitored and maximum contaminant levels (MCLs) have been established for certain metals and acid concentration (pH) in drinking water. Private water supplies in rural areas are not monitored and it is up to the owner or consumer to test and treat their water.
Ground water contamination from stockpiles is due to unprotected storage of substances which may leach into soil or run-off into streams during precipitation or irrigation. This includes de-icing salts at highway maintenance lots, reclaimed metal stockpiles, coal, metallic ores, phosphates, and gypsum (1). Highway salts are made from sodium or calcium chloride, sand, and anti-caking additives such as ferric ferrocyanide and sodium ferrocyanide. Coal and metallic ores may cause acidic drainage. Acidic leachate can dissolve metals and ores releasing more contaminants into the waste stream.
Tailings are low grades of mining ore that are disposed of on the land surface and often in mining waste ponds(1). Because they are unlined, these ponds can be a source of acids or metals, which are carried in run-off or leachate.
Spoil consists of mining debris and waste. A major source of acid-mine drainage is iron-sulfide-rich spoil associated with coal mining, and spoil from metal sulfide mines, such as copper and gold mining operations (1).
1. EPA Handbook: Groundwater. Vol. 1: Ground
Water and Contamination. September 1990. USEPA Office of Research
and Development, Washington DC.
This page was prepared by T.L.
Pedersen , UCD EXTOXNET FAQ Team.