Planning Coal Slurry Refuse Impoundments - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 35

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Planning Coal Slurry Refuse Impoundments
This chapter summarizes the current engineering elements of the design,
operation, and reclamation of coal refuse impoundment systems. The chapter
addresses these elements in relation to the Appalachian coal region, where
impoundments are often located in steep valleys. It is not a comprehensive
overview of all engineering design options, but a description of the major
elements currently implemented in the planning and design of coal slurry refuse
impoundments. The engineering design process is specific to the conditions of
each particular site: What works in one circumstance may not work in another.
The position of potential fluid pathways—such as coal seams, mine
workings, and fractures—relative to an impoundment is a significant factor in
the design of new and modifications to existing coal refuse impoundment
systems in the Appalachian region. Most impoundments in Appalachia utilize
the natural topography to form the storage basin that will contain the slurry.
This is often accomplished by constructing an embankment at the mouth of a
small valley or watershed to complete the basin structure used for storage. The
stream channel at the base of the basin selected for the impoundment defines
the approximate level of local drainage. Coal seams and mines that do not crop
out above the level of the stream channel are termed below-drainage, whereas,
those that crop out along the valley wall above the stream channel are termed
above-drainage ( Figure 3.1 ). In some locations, both above- and below-drainage
coal seams (and mines) may be present.
The relative elevations of local drainage and slurry height can be critical.
For example, during the filling of the impoundment, if the slurry elevation
exceeds the level of an above-drainage coal mine, the mine could become
submerged and provide a hydraulic conduit for the slurry. In addition, below-
drainage workings can be in hydraulic connection with slurry through less
direct means, such as fractures. Both above- and below-drainage mine workings
require specific engineering considerations.