Environmental Engineering Reference
In-Depth Information
plants. A large coal-fi red power plant can generate about 1 gigawatt of
electricity if operated continuously, that is, with no shutdowns for main-
tenance—enough to power 1,200 homes in the Northeast but fewer
homes in the South, where air conditioning is common.
It currently is the lowest-cost source of energy, at just 3 cents per
kilowatt-hour. Coal is literally cheaper than dirt, about a penny or two
a pound. Topsoil costs more than that. But if coal's heavy environmental
costs such as pollution and health losses are added, the cost rises to 10
or 15 cents per kilowatt-hour, making it one of the most expensive
sources of power.
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Mining
Thirty-one percent of America's coal is mined at the surface and 9
percent underground. Because of the extensive use of computer-regulated
automation, coal mining today is more productive than in the past, and
mining personnel must be highly skilled and well trained in the use of
complex, state-of-the-art instruments and equipment. Many jobs require
four-year college degrees. The increase in technology has signifi cantly
decreased the mining workforce from 335,000 coal miners working at
7,200 mines fi fty years ago to 105,000 miners working in fewer than
2,000 mines today. The decrease in mine numbers and miners does not
indicate a declining industry: coal production doubled between 1965 and
2005.
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The Department of Energy forecasts that coal use will increase
at the expense of oil during the next two decades.
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Surface Mining
Coal is mined at the surface if the seam is less than
about 180 feet below the surface. However, if the coal seam is very
thick, economical surface mining may extend to a depth of 300 feet.
A particularly noxious surface mining practice in Appalachia is moun-
taintop mining, a process used when near-surface coal seams are thin
but numerous. (About 14 percent of the coal used to generate elec-
tricity is obtained by mountaintop mining.) Enormous bulldozers and
draglines scrape away mountain tops to expose the coal seams, and
the coal is then trucked away. The leftover dirt and rock are dumped
into adjacent valleys and streams. This method leaves ridge and hill-
tops as fl attened plateaus and is highly controversial because it covers
streams and disrupts ecosystems. Mountaintop mining has clipped the
tops off 500 mountains and buried 2,000 miles of streams (fi gure
6.7). Environmentalists regard this as domestic terrorism by home-
grown terrorists.
