Drainage (AMD)
problem metals such as iron, aluminum, manganese, and low pH levels from abandoned coal mines and other poor mining practices predating mining laws and regulations.
Causes: Acid mine drainage is caused by polluted water flowing from, or caused by, deep mining, surface mining, or left over coal refuse piles (commonly referred to as gob piles). This drainage is usually orange in color and may be acidic or alkaline with high levels of dissolved metals. AMD can lower water quality and impair aquatic life.
Pyrite, an iron sulfide mineral, is frequently found in coal mine refuse piles and underground coal mines. When water and air come in contact with acidic material such as pyrite, there is a chemical reaction. It produces iron hydroxide and sulfuric acid, which contaminates surface and sub-surface waters. This contamination is known as acid mine drainage.
pyrite (in coal) + oxygen + water = iron hydroxide + sulfuric acid +
aluminum +manganese + sulfate = Acid Mine Drainage
Acid mine drainage often occurs in the down-dips of underground coal mines. AMD forms in the void space where the coal was exploited long ago. In the abandoned coal mines there are coal pillars supporting the roof of the mine and waste coal that was left behind. This coal contains the pyretic materials needed to make sulfuric acid once exposed to air and water. Air enters the mine due to the void space left during mining and through fractures in the overburden. Water also enters the mine through fractures and subsidence features. Subsidence features form when the ‘rooms’ of a coal mine collapse leaving moderate to large depressions in the earth. Rainwater and surface stream water funnels down through these holes and collects in the collapsed mines providing the needed air and water for the AMD reaction to occur. Then the AMD drains down-dip through the mine until it reaches an old portal (a mine opening) and then drains into the surrounding streams. In some cases the portals to the mines were closed off and the mine water collects until the water pressure busts a hole up to the surface where the overlying rock is weak or very thin. This mine water then drains to the surrounding stream.
Effects: AMD from mining, both surface and underground, discharge to surface waters and leaches into the groundwater system. In surface waters, AMD results in low pH and elevated metals concentration (i.e. iron, aluminum, and manganese). This degrades habitat allowing the survival of only the most pollution tolerant aquatic species. In groundwater, high mineralization from AMD renders the water supply source unpotable. A complete review of surface water quality effects resulting from acid mine drainage is provided within the AMDAT plan In addition, sediment from unreclaimed surface mines aggrades the stream channels causing a loss of habitat and increases flood frequency. The extent of sedimentation within this watershed needs to be quantified.
Wildlife habitat within the Huff Run Watershed has been severely impacted by previous surface mining activities, both reclaimed and unreclaimed. Indigenous terrestrial species have been subjected to the loss of significant amounts of habitat as a result. Reclaimed areas, although providing some cover, have been converted from forested to grasslands, creating an alternate prairie like habitat which is not its original form. Significant positive impacts on local populations of wildlife could be achieved if reclamation and reforestation projects would be implemented. Restoring unreclaimed areas to their approximate original contour and establishing vegetation would provide wildlife habitat. In addition, reforestation of reclaimed grasslands would provide much needed quality habitat for wildlife indigenous to the region’s forested areas.
The environmental quality of the forested areas has been severely impacted by the unreclaimed surface mines and discarded tailings from deep mines. The unreclaimed areas have open highwalls, pit impoundment, exposed gob and spoil ridges. Many of the exposed gob and spoil ridges lack vegetation due to acid soil conditions and/or inadequate topsoil. These areas can be reclaimed to the approximate original contour and planted in trees and grasses enhancing wildlife habitat. In some areas vegetation has reestablished overly successful populations of opportunistic plant species. Here, species such as wild grape inhibit the growth of a diverse woodland plant community.
page on AMD.
USGS AMD information
Office of Surface Mining AMD info
