Introduction - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 8

rock, and most of that coal is shipped raw without extensive processing.
Consequently, coal waste impoundments are rarely used in the West. In the
Eastern coalfields, however, the majority of the coal from underground mines is
processed before sale. Of the 1.1 billion tons of coal mined in the United States
per year, about 600-650 million tons are processed to varying degrees.
Typically 350-400 million tons are handled in wet-processing systems that, on
average, produce 70-90 million tons of fine refuse in a slurry. (C.Raleigh, CQ
Inc., personal communication, 2001). Much of that material is stored in coal
waste impoundments.
Disposal methods for coarse and fine coal refuse developed along separate
lines. Even before the days of modern coal preparation plants, laborers picked
rock from the run-of-mine coal and discarded it in refuse piles. Sometimes
coarse refuse was returned to the mine, but more commonly it was deposited on
the surface.
When fine coal cleaning came into widespread use, it became necessary to
deal with the refuse. One way is to pump the slurry into an impoundment and
allow the particles to settle. Another is to concentrate or dewater the slurry and/
or to mix it with coarse refuse or other additives (e.g., lime, sodium silicate,
elastomeric polymers, resinous adhesives) to provide stability (Osborne, 1988),
and then dispose of it in a landfill or impoundment.
DISPOSAL OF FINE REFUSE IN IMPOUNDMENTS
To impound fine coal slurry, embankments are constructed with
compacted coarse coal refuse material. Prior to an accident in 1972, the Buffalo
Creek disaster ( Sidebar 1.3 ), little consideration was given to control of water
entering an impoundment from a preparation plant or as runoff from the
watershed above. Indeed, the coarse coal refuse used for embankment
construction provides a filter to limit impacts to the quality of the water entering
nearby streams (D'Appolonia Consulting Engineers, 1975). In most
impoundments, the embankment is constructed of coarse coal refuse, according
to a design that is approved by regulatory authorities (see Chapter 2 ).
In the mountainous Appalachian region, the coarse refuse embankments
are usually constructed across a valley, enclosing a basin that holds the coal
refuse. In flatter Midwestern terrain, bermed and incised impoundments may be
constructed. They typically have a larger surface area and are shallower. The
slurry is pumped into the impoundment, where the fine particles in the slurry
settle by gravity beneath a pool of clear water. In many impoundments, this
clear water is pumped back to the coal processing plant and is reused.