After surface mining, workers replace the overburden, grade it, cover it with topsoil, and fertilize and seed the area. These steps help restore the biological balance of the area and prevent erosion. The land can then be used for croplands, wildlife habitats, recreation, or as sites for commercial development. Although only about 32 percent of the nation's coal can be extracted by surface mining, some 63 percent of all U.S. coal is mined using this method today. Because surface mining is typically much cheaper than underground mining.
Underground mining is used when the coal seam is buried several hundred feet below the surface.
Mine shafts may sink as much as 1,000 feet deep. With this method, much of the coal must be left behind to support the mine's roofs and walls. Sometimes as much as half the coal is left behind in large column formations to keep the mine from collapsing. A more efficient and safer underground mining method, called longwall mining, uses a specially shielded machine which allows a mined-out area to collapse in a controlled manner. After coal comes out of the ground, it typically goes on a conveyor belt to a preparation plant that is located at the mining site.