Mining processes result in large amounts of toxic waste, which need to be disposed of or stored. In developing counties, due to lax regulations, large amounts of mine tailings are simply sent into rivers, resulting in considerable ecological damage and contamination or human water supplies. In the United States, mines have faced progressively stricter regulations meant to reduce the spread of toxic mine byproducts. Older abandoned mines often have exposed tailing piles that are poorly contained. Particulate mine tailings can be carried by wind to contaminate broad areas, including waterways. Modern mines utilize a variety of containment methods, including pond storage, which minimize but do not completely eliminate the spread of toxins into water sources. While mining regulations have become stricter, mining technologies result in higher productivity, leading to larger amounts of mining waste.
Mines invariably contaminate surface and ground water, even when mines have containment systems in place. Chemicals such as sulfer, arsenic, mercury and cyanide seep into ground water during mining operations, or get washed away by rainwater, collecting in rivers, lakes and aquifers. Many abandoned mines leave toxic waste dumps that leach chemicals and heavy metals for decades, much of which ends up in water sources. Acid mine drainage frequently occurs with coal mines, polluting waterways and destroying terrestrial habitats in large areas surrounding the mines.
Some mining methods, such as strip mining and mountaintop removal, remove large areas of surface vegetation and rock, often depositing the material in nearby land depressions. The depressions are usually water drainages. These mining practices can destroy local riparian systems -- the ecosystems along water systems or bodies of water -- resulting in diversion of water to other locations. These processes also effectively contain waste, causing local water source contamination from acid mine drainage.
Many mining operations utilize large volumes of water, diverting local water resources away from other uses. Disposal methods for waste water are highly variable and depend to a large degree on local regulations. In many developing countries, waste water containing toxic chemicals can be discharged directly into the water supply. In the United States, waste water permitting is generally handled on the state level, resulting in different standards depending on the locality. Because mining lobbies and environmental groups are constantly advocating on opposite sides of the issue, mining waste and water quality regulations also vary significantly over time.