The area mining method is commonly used to mine coal in the flat to moderately rolling terrain found principally in the Western and Midwestern States. In this method, the overburden is excavated down to a coal seam and then the mining area is enlarged horizontally to expose and remove the coal.
In the West, coal seams are commonly 10 to 20 feet thick, with up to 100-foot seams in the Powder River Basin of Wyoming; in the Midwest coal seams are typically 3 to 7 feet thick and 75 to 100 feet below the surface. The life of some mines in the West may be more than 50 years. Because many area mines are extremely large and operate in places with few if any residents or neighboring businesses, enormous equipment can be used in removing overburden and reconstructing the land.
The area mining operation in the illustration is on land that was formerly used for farming. As can be seen, the agricultural use is being reestablished immediately following reclamation. The mining is proceeding across the land toward the left side of the area. The initial excavation was made far enough away from the stream along the right edge of the area to prevent damage to the stream.
The coal under most of the area has been removed, and reclamation has been completed on some of the land. For example, some of the cattle in the foreground and those in the feedlot behind the silo are grazing on reclaimed land that was previously mined by this operation.
On the far left of the illustration, the topsoil from the unmined area is being removed by scrapers, transported across the area of active mining, and immediately spread on the land on the right that is being reclaimed. (Reclamation of the land as soon as practical is called contemporaneous reclamation. It’s required by the Surface Mining Law.) A large stockpile of topsoil in the center background of the operation, removed from the initial mining cut, has a grass cover to prevent erosion and will be spread over the last mined area to be reclaimed.
After blasting, the loosened overburden is removed by dragline and is dumped onto an adjoining previously mined area in one motion. In some mining operations, overburden is removed with power shovels, bulldozers, or scrapers rather than with draglines.
The exposed coal seam can be seen where the overburden has been removed. The coal is removed with power shovels and loaded into large trucks, which carry the coal to the preparation plant (behind the dragline). After the coal goes through the plant, it is loaded into railroad cars, possibly for transportation to an electric generating plant, or to a port loading facility for export.
The ridges formed by the dragline as it dumps the overburden are regraded with bulldozers. Then topsoil is spread to provide a finished surface similar to the surface before mining. The land is then tilled using traditional farming methods and, as shown, crop- and pasture land are reestablished. After reclamation is completed, the productivity of the land will be similar to its productivity before the mining operation began, possibly higher.
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