Alternatives for Future Coal Waste Disposal - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 143

Controlled placement is used where underground workings are accessible.
This method has a number of inherent advantages over blind flushing. First, the
engineer can verify the accuracy of the maps, inspect the condition of the
openings, and better estimate the available space. Second, and possibly more
important, bulkheads can be constructed to control the direction and extent of
flow. Finally, collection and reuse of the water is more practicable.
Once areas have been identified and properly confined, controlled flushing
can proceed similarly to blind flushing. However, in controlled flushing, the
slurry can be delivered to the underground opening by a pipeline that enters the
mine through a borehole or other opening and then extends laterally through the
mine to the desired location. This allows the operator to begin filling the most
remote part of the mine and then to withdraw the pipeline in stages as the voids
are filled and sealed. The advantages of this method are greater certainty of the
location of the slurry, better utilization of available space, and better reuse of
the water needed to transport the refuse. This method also protects against
subsidence. One of the main concerns is the safety of workers in the mine
receiving the slurry and in any adjacent, down-dip mines.
The committee concludes that although there are alternatives to disposing
of coal waste in impoundments, no specific alternative can be recommended in
all cases. Acceptable alternatives are highly dependent upon regional and site-
specific conditions. Also, the alternatives that have been identified are in
varying stages of technological development and implementation. One of the
factors limiting implementation to this point has been the cost associated with
the various alternatives. Additional research is needed to develop these
alternatives further and to evaluate the economics of these processes. The
committee recommends that a screening study be conducted that (1)
establishes ranges of costs applicable to alternative disposal options, (2)
identifies best candidates for demonstration of alternative technologies for
coal waste impoundments, and (3) identifies specific technologies for which
research is warranted. Input from MSHA and OSM regarding regulatory
issues will be valuable to such a study.
REMINING SLURRY IMPOUNDMENTS
While coal waste impoundments have generally been viewed as permanent
disposal sites, there may be situations in which impoundments can be a resource
( Sidebar 7.6 ). In the past, recovery of fine coal was not as efficient, resulting in
many older slurry impoundments containing significant