All mining activities create considerable waste, including acid runoff and chemical byproducts of refining. Coal mines are particularly prone to acid runoff. When large amounts of rainwater enters functioning or abandoned mines, the water becomes acidic and contaminated with heavy metals. The Environmental Protection Agency estimates that 40 percent of western U.S. watershed have been contaminated by mine waste. In the United States, the mining industry is the top toxic polluter. The problems are frequently more pronounced in under-regulated developing countries, where mining companies can be free to pollute with impunity. Water pollution from mines has been known to decimate aquatic life, and seriously impact bird and mammal populations. Water sources used by humans have also been contaminated, posing serious risks to human health.
Mining and land-based drilling significantly alter landscapes and wildlife habitat. The process often disturb thousands of acres of land directly surrounding extraction operations. Peripheral infrastructure also alters habitats, including roads, worker residences and industrial complexes. Open pit mines and mountaintop removal techniques remove all surface fauna and topsoil to reach metals and minerals below. in the best-case scenario, mining and drilling companies perform reclamation work to rehabilitate damaged ecosystem. While the United States often required reclamation, most developing countries do not, resulting in badly degraded landscapes and abandoned facilities that continue to leach pollution long after operations have ceased.
The process of drilling has numerous impacts on ecosystems and wildlife. Any off-shore drilling operation is preceded by seismic exploration, which is known to disorient whales and lead to mass beachings. Oil and natural gas drilling produce numerous byproducts that are often released into the environment, such as brine waste water containing heavy metals, and produced water in oil drilling, which can contain numerous toxic chemicals. Drilling companies in the U.S. are required to dispose of waste byproducts according to specific environmental laws. One disposal method uses deep injection wells to store the waste, potentially polluting ground water. Oil spills on land and at sea present another hazardous environmental impact.
With the massive oil spill in the Gulf of Mexico in 2010, the environmental consequences of off-shore drilling became a major focus for the entire world. The Deepwater Horizon spill lasted for over three months, releasing millions of barrels of oil into the sea. The oil destroyed ocean habitat, killed wildlife and contaminated coastal ecosystems. The clean-up operation used the controversial dispersant Corexit to break up the oil. Approximately two million gallons of Corexit were dumped into the Gulf, with unknown consequences.