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Acid mine drainage,
sometimes referred to as AMD, results when the mineral pyrite (FeS2)
is exposed to air and water, resulting in the formation of sulfuric acid
and iron hydroxide. Pyrite is commonly present in coal seams and in the
rock layers overlying coal seams. AMD formation occurs during surface
mining when the overlying rocks are broken and removed to get at the coal.
It can also occur in deep mines which allow the entry of oxygen to
pyrite-bearing coal seams.
The products of AMD formation, acidity and iron, can devastate water
resources by lowering the pH and coating stream bottoms with iron
hydroxide, forming orange-colored soil common in areas with abandoned mine
drainage. Many areas also contain naturally occurring limestone (CaCO3)
deposits which neutralizes acidity. To determine whether or not a mine
will create acidic drainage, a watershed must be analyzed to determine how
much pyrite and neutralizers are in the rocks which will be disturbed by
mining. Systech
enhanced WARMF to simulate AMD as nonpoint source
load. A kinetic expression was used to simulate pyrite oxidation as
a function of oxygen in the soil voids. The by-products of pyrite
oxidation were calculated according to its mass action equations.
Chemical equilibrium was used to account for the speciation of ferrous and
ferric irons and precipitation of metal hydroxides. The modified
WARMF was applied to the Cheat River of West Virginia and Chartiers Creek
watershed of Pennsylvania. The calibrated models were used by USEPA
to calculate TMDLs. These TMDLs have since been approved
for their respective states. Check our journal
articles, conference publications, and
reports
sections for more information. |
AMD site in West Virginia
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