coal mines. Wyoming—the largest coal-producing state in the country—has no coal preparation plants, largely because the subbituminous Powder River Basin coal is low in ash. However, PRB coal has a high level of inherent moisture (~30 percent), which has stimulated some interest in thermal dewatering of the coal to increase its heating value and reduce its transportation costs (see Box 4.2).


The conditions that will be encountered in future coal mines will undoubtedly be different from those of today—the more easily mined coal has already been extracted. As shallower coal is depleted and seams with greater amounts of overburden6 are mined, surface mining will become more expensive because stripping ratios7 will increase and multiple benches8 will be needed. This will increase the number of unit operations and the associated cost. In underground mining, the mines of the future will have to access seams that are deeper, thinner, or thicker, often with higher gas content and potentially with greater ground-control issues. Overlying or underlying seams may have been mined, or it may be necessary to mine multiple seams simultaneously to meet increased production requirements. These more difficult mining situations will have an effect on economic decisions related to mine profitability, on the health and safety of mine workers as they encounter more challenging or different mining requirements, on the technical ability to mine, and on the management of waste materials generated by mining.

Small mines (i.e., with annual production less than 2 million tons), which currently produce more than 25 percent of coal in the United States, play an important role in ensuring adequate coal supply because they have historically started and ceased production as demand and prices fluctuate. They also play a critical role in fully utilizing national coal resources, particularly those resources that may not be mined by larger operations.9 The population of small coal mines has been decreasing and is projected to continue to decline. However, small mines will continue to exist, and the technical and societal issues they will face in the future should be considered in agency plans.

Miner Health and Safety

Although statistics show substantially improved health and safety conditions in mines in recent years—with continuous decreases in both the incidence and


Overburden is the overlying rock and soil that must be removed to gain access to a coal seam to be mined.


The ratio of overburden thickness to coal thickness; may also be measured by weight or volume.


If overburden exceeds a certain thickness, equipment size requires that the overburden is removed in more than one pass leaving a flat bench for equipment access between each pass.


Larger mining companies will only mine when sufficient coal reserves are available to sustain the considerable capital investment required for advanced mining equipment and technologies.

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