Abandoned mine drainage (AMD) is a form of pollution that deposits metals into our watersheds. It can be either acidic or alkaline in nature and originates from abandoned surface mines, deep mines and from gob piles (a.k.a. bony piles).
Acid mine drainage is caused by the weathering of pyrite found on the surfaces of underground mine voids and on discarded coal refuse materials located on the surface of the ground. When the pyrite weathers, it causes water to become acidic which in turn dissolves aluminum and manganese found in the underlying soils and clays. When aluminum and manganese dissolve, they increase the content of iron and sulfates within the water causing pollution.
Alkaline mine drainage is caused by groundwater coming into contact with limestone. Once groundwater contacts the limestone, it becomes alkaline. The alkaline groundwater may then flow into underground mine voids and neutralize the mine water. Even though the mine water is neutralized, dissolved metals may still be present due to the lack of oxygen.
AMD kills stream life, destroys wildlife habitat, contaminates drinking water, spoils natural beauty and deters recreational activities and tourism opportunities.