|Surface Coal Mining|
Surface coal mining techniques, which account for the majority of national coal production and roughly 42 percent of West Virginia’s coal production, involve the mechanical removal of overlying native earth and rock or “overburden” to reach underlying coal seams. Surface mining can be further categorized into three basic operational methods: contour mining, area mining and mountaintop removal mining. All three forms of surface mining are generally referred to as “mountaintop mining”. Secondary extraction methods can also be employed with surface mining, usually through a process known as highwall mining. While surface mining includes a variety of methods, certain criteria used to determine the exact operation, layout and the extent and form of coal extraction are applicable to all forms of surface mining.
Included in the criteria that are transferable to all forms of surface mining are mining and reclamation considerations. Before any permit is issued under SMCRA or a state delegated program, the operator must submit a specific mining and reclamation plan for review and approval by the regulatory authority. The components of the mining and reclamation plan include a variety of issues such as initial mine development, final mine design, backfilling and regrading, achieving Approximate Original Contour or “AOC” (explained in greater detail in subsequent sections) and erosion and sediment control. Reclamation considerations, along with stripping ratios (explained in subsequent paragraph), are usually the dominant factors that dictate the form of surface mining that is used to extract a coal reserve.
In addition to permitting considerations, determining the extent to which a coal seam or block of coal seams is economically feasible for mining is an integral part of determining the method of surface mining used to extract the reserve. The typical method of assessing surface mining economics for a coal seam is a calculation of overburden (native rock and soil above a coal seam) moved per clean ton of coal produced, commonly referred to as “mining ratio”. The higher the mining ratio (or more overburden moved per clean coal ton), the higher the cost of producing coal. In situations where a given coal reserve includes more than one coal seam, the recoverable coal volume from the multiple seams is factored together to lower the overall mining ratio for the entire coal reserve. Because mining more than one seam lowers the mining ratio for a mining project and increases its economic potential, it allows for extraction of coal seams that would be uneconomic to recover by themselves.
The economic viability of a surface mining project, calculated through the mining ratio, is highly mine and coal reserve dependent. Site-specific factors such as overburden type and depth, excavation costs, coal value and overburden haulage distances and costs are all considered in the development of stripping ratios for a particular mine site and coal reserve.
The ability to construct valley fills is paramount to the economic and physical viability of a surface mining project. As explained in more detail in the following sections, all surface mining methods need valley fills for placement of excess overburden. Without the ability to construct fills, surface mining becomes physically impossible in the steep terrain of Appalachia and West Virginia.