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Impacts of mine drainage on aquatic life, water uses, and man-made structures

Jane Earle and Thomas Callaghan
Department of Environmental Protection
Harrisburg, PA 17105

"...The influx of untreated acid mine drainage into streams can severely degrade both habitat and water quality often producing an environment devoid of most aquatic life and unfit for desired uses. The severity and extent of damage depends upon a variety of factors including the frequency, volume, and chemistry of the drainage, and the size and buffering capacity of the receiving stream", (Kimmel, 1983).

Drainage from underground coal mines, surface mines, and coal refuse piles is the oldest and most chronic industrial pollution problem in the Appalachian Coal Region. In 1995, 2425 miles (3902 km) of stream in Pennsylvania did not meet EPA-mandated in-stream water quality standards due to over a century of mineral extraction (PA DEP, 1996). The unfavorable repercussions of coal mine drainage in the northern Appalachian Coal Region have been documented in the literature for over a century. It is believed that the first reference to what we now call acid mine drainage in North America was made by Gabriel Thomas, who in 1698 reported: "...And I have reason to believe that there are good coals, also, for I observed the runs of water which have the same color as that which proceeds from the mines in Wales..."

Pyrite in coal and overlying strata, when exposed to air and water, oxidizes, producing iron and sulfuric acid. Ferric iron, when discharged to surface water, hydrolyzes to produce hydrated iron oxide and more acidity. The acid lowers the pH of the water, making it corrosive and unable to support many forms of aquatic life. Acid formation is most serious in areas of moderate rainfall where rapid oxidation and solution of exposed minerals can occur. Indeed, of the 19,308 km of United States streams reported degraded by acid mine drainage in 1970, 16,920 km or 88 percent were located east of the Mississippi River in the Appalachian coal fields of Pennsylvania, West Virginia, Ohio, eastern Kentucky, Tennessee, Maryland, and Alabama (Warner, 1970). Various impacts range in severity from isolated nuisance type problems to severe water quality impacts affecting large volumes of groundwater and miles of watercourse. Impacted uses include agricultural (irrigation and livestock), industrial, and potability of water supplies along with recreational uses, scenic resource appreciation, and aquatic organism habitat. The aggressive nature of mine drainage may also result in corrosion and encrustation problems with respect to such man-made structures as pipes, well screens, dams, bridges, water intakes, and pumps. The compromising of well casings (water supply or oil and gas wells) can be extremely troublesome because it can then allow the migration and co-mingling of water from one aquifer with another, often leading to inter- and intra- aquifer contamination (Merritt and Emrich, 1970). Acidic mine drainage in particular can also be toxic to vegetation when recharging to the shallow groundwater system and soil water zones.

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