Environmental Engineering Reference
In-Depth Information
vegetation, and food species. They may require habitat enhancement and management to be of
significant value to wildlife (OSM 1979).
COAL SEAM FIRES
Fires sometimes occur in coal beds underground. When coal beds are exposed, the fire risk is
increased. Coal seam fires cause serious hazards to health, safety, and the environment, including
smoke and toxic fumes; reigniting grass, brush, or forest fires; and subsidence of surface infra-
structure such as roads, pipelines, electric lines, bridge supports, buildings, and homes. Almost all
fires in solid coal are ignited by surface fires caused by lightning or people clearing land with fire
or burning trash or brush in the presence of outcrop deposits of coal or peat. Coal seam fires may
continue to burn for decades until the fuel source is exhausted, a permanent groundwater table is
encountered, the depth of the burn becomes greater than the ground's capacity to subside and vent,
or humans intervene. Coal seam fires are particularly insidious because they continue to smolder
underground after surface fires have been extinguished, before flaring up and restarting forest and
brush fires nearby. Because they burn underground, coal seam fires are unlikely to be extinguished
by rain (Whitehouse and Mulyana 2004, 95). Coal refuse dumps are susceptible to spontaneous
combustion and represent a significant potential source of air pollution. In 1978 the Environmen-
tal Protection Agency (EPA) reported there were 250 million metric tons of burning coal refuse
in the United States, in addition to fires in abandoned mines and along outcrops of exposed coal
(Chalekode and Blackwood 1978). These fires emit various pyrolysis and combustion air pollutants
that may contribute to deterioration of air quality in the vicinity of coal-cleaning plants.
PROCESSING COAL
Coal cleaning, or washing, removes slate, clay, carbonaceous shales, pyrite, and rock aggregate
from the coal product to meet specifications of purchasers. The many processes for cleaning coal
produce toxic wastes, fugitive dust, and noise. Coal preparation plants, with associated raw coal
storage and waste disposal areas, are typically situated at the mine site and considered part of the
mine area.
When the cleaning process is completed, waste or refuse material is disposed of in solid and
liquid forms. Solid waste, or gob, is piled in spoil banks or waste piles near the preparation plant.
Because storage of waste requires large areas of land, a preferred disposal method is to return
this waste to the mine for permanent burial, isolating it from surface water and groundwater.
Gob piles can have many detrimental effects. Depending on the method used to pile and contain
the waste, the refuse may be unstable and subject to slope failures and landslides (Nunenkamp
1976). In 1972 a coal mine waste dam failed near Buffalo Creek, Virginia, releasing water and
debris that killed 125 persons. The U.S. Army Corps of Engineers inspected many similar dams
and found 50 to 60 percent to be potentially hazardous (Dvorak 1977). Runoff from gob piles
is a source of significant acid drainage (Martin 1974). Liquid waste, or slurry, contains high
proportions of suspended sediments consisting of fine coal particles, heavy metals, and other
trace elements and contaminants. Slurry is generally pumped to a series of ponds where sedi-
ments settle out by gravity and water is clarified before discharge to streams or rivers. These
ponds must be cleaned out periodically to maintain sufficient depth to be effective (Hamilton
2005, 158).
Waste material discarded at prep plants may contain over 80 percent marketable coal fines,
and more than 20 percent of the coal extracted from a mine may be lost unless a fine coal
 
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