Acid Mine Drainage

Acid mine drainage is just one of the negative environmental effects that old underground mines have on the state of Pennsylvania.

The diagram below from the U.S. Geological Survey shows the distribution of coal-bearing strata in the Appalachian region study area, which includes Kentucky, Maryland, Ohio, Pennsylvania, Virginia and West Virginia.

Key to the map:

• Dots = corehole locations
• Green = low potential for acid mine drainage (AMD) from surface mining
• Yellow = intermediate AMD potential
• Red = high AMD potential

Note that significant environmental damage from AMD can occur even in areas with low AMD potential.

Source: USGS

The Hughes Bore Hole is located southwest of Altoona, Pennsylvania near the small town of Cassandra.  This is a site of serious acid mine drainage into the Little Conemaugh River.  Prepare to be totally disgusted.  (Warning: Adult language)

Acid mine drainage is a global problem.  Several thousand AMD pollution sites exist worldwide.  In the U.S., AMD from coal mines has adversely impacted over 8,000 miles of streams in Pennsylvania, West Virginia, Ohio and Maryland alone.  The problem in the western United States is less studied, but once-pristine watersheds are also now suffering from the effects of AMD.

Cleanup of abandoned mine sites is often challenging because of their remote locations.  Unfortunately, without human intervention to clean these toxic locations, AMD problems will persist for hundreds of years until the mineralized rock is leached free of sulfides and metals.

Visit Wikipedia for a list of mining sites and river systems significantly affected by AMD.

Orange is the color that usually comes to mind when someone mentions acid mine drainage (AMD).  But AMD can manifest itself in many different colors:

	ORANGE:  Orange is the most common AMD color.  The orange material is iron oxide, which is basically rust.
	YELLOW:  When the pH of AMD is raised past 3, either through contact with fresh water or neutralizing minerals, previously soluble Iron(III) ions precipitate as Iron(III) hydroxide, resulting in a yellow-orange solid colloquially known as yellow boy.
	WHITE:  If the AMD discharge is white, it has especially high concentrations of aluminum.  As the water becomes less acidic, the aluminum combines with oxygen to form solid particles that cause a “milky” appearance or white coating.
	BLACK:  If the AMD discharge is black, it has especially high concentrations of manganese.
	CLEAR:  Ironically, the worst AMD is clear because the water is so highly acidic that the minerals remain dissolved and do not precipitate away.  Water bodies that are this acidic cannot support much life.

Overburden is a term used in mining and archaeology to describe material that lies above an area of economic or scientific interest.  For example, the rock, soil and ecosystem that lies above a coal or ore seam is called overburden.  Mining companies also call this “waste,” though environmentalists might argue that it’s the overburden that actually has value.  Overburden is removed during surface mining, but it’s typically not contaminated with toxic components, and therefore may be used to restore an exhausted mining site to some semblance of its appearance before mining began.

A related term is interburden, which is the material that lies between two areas of economic interest, such as the material separating coal seams.

Tailings is the material that remains after economically valuable components have been extracted.  As mining techniques and the price of minerals increase, tailings are often reprocessed using new methods to recover additional minerals.

Adapted from Wikipedia

Acid mine drainage typically has four key characteristics (though not all drainages have all four characteristics):

• High acidity (hence the name “acid mine drainage”)
• High metal concentrations (iron is most common)
• High sulfate levels
• Excessive suspended solids (which smothers insects and other aquatic life)

Adapted from SCRIP

Acid mine drainage (AMD) is the outflow of acidic water from (usually abandoned) metal or coal mines.  AMD may also occur in other areas where the earth has been disturbed, such as construction sites, subdivisions, transportation corridors, etc.  AMD is also typical downstream from coal stocks, coal handling facilities, and coal washeries.

AMD occurs when mineral pyrite (FeS2) is exposed to air and water, resulting in the formation of sulfuric acid and iron hydroxide.

Water that comes in contact with pyrite usually turns a characteristic orange-red or yellow-orange color.  The orange material is iron oxide, which is basically rust.

Adapted from Wikipedia.