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