Mining can be an extremely destructive practice that often has very negative impacts on the surrounding environment. The material that is mined for is surrounded by other ore and rock, and the mining process creates large amounts of tailings (the waste material from the ore processing phase that often contain toxins along with small amounts of heavy metals).
Waste material from mines that contain metal sulfides can lead to sulfuric acid drainage. Tailings also contain minerals and materials that can lead to dangerous runoff and water contamination when stored improperly. Some mine waste and tailing dump sites are structurally unsound and often overflow and break, allowing contaminants to spill out over the surrounding environment. In some cases, mines will have long pipes or waste canals that carry tailings to waterways for dumping.
Disposal of mine tailings is usually the single biggest environmental concern facing a hard rock metal mine, and creates very long-term environmental liabilities which future generations must manage.
Wet storage in pits or lakes requires facility maintenance and perpetual water treatment. Tailings are disposed as wet med and held in pits lined with clay or a synthetic material; existing valleys sealed off with earthen dams; natural lakes; or put back into the original mining pit.
On-land dry stack storage requires a high upfront cost and perpetual treatment and maintenance. Tailings are dried into a solid matter, transported by truck or conveyer instead of a pipeline, and are buried in a covered and lined pit.