|State/Province||Major coal-producing region||Number of mines||Production millions of tons||Total employment||Reverse base millions of tons||Exports percentage|
|Montana||Fort Union North Central Powder River||8||41.00||708||48,815||75|
|New Mexico||Raton Mesa||1||1.25||40|
|North Dakota||Fort Union||6||29.58||657||9,470||0|
|Wyoming||Powder River Bighorn||20||20||266.58||2,777||25,971||90|
The Great Plains' coal resources occur in nine major regions, but the bulk of resources and production occurs in the five coal regions of the Northern Great Plains and Prairie Provinces. These five regions, which contain lowrank subbituminous and lignite coals of late Cretaceous to early Tertiary age, are the Great Plains Coal Region of Alberta; the Fort Union Coal Region of western North Dakota, eastern Montana, southern Saskatchewan, and southwestern Manitoba; the North Central Coal Region of north-central Montana; and the Powder River and Big Horn Coal Regions of northern Wyoming and southeastern Montana. Major coal deposits in the Southern and Central Plains include the high-sulfur bituminous coals of eastern Kansas (the Western Interior Coal Region) and north-central Texas (the Southwestern Coal Region), the low-sulfur bituminous coking coal of northeastern New Mexico and southeastern Colorado (the Raton Mesa Coal Region), and the subbituminous coals in the Denver Coal Region of northeastern Colorado and southeastern Wyoming.
Coal has provided a local source of fuel for Great Plains farms, ranches, towns, railroads, and industries from early European American settlement into the modern era. By the end of World War II, production in the Plains had peaked at just a few percent of the more than 600 million tons mined in the United States and Canada. Production bottomed out in the late 1950s and early 1960s, reflecting increasing displacement of coal by oil and gas. Beginning in the late 1960s, however, a growing demand for electrical power, concerns over oil and natural gas supply, and the demand for coals low in sulfur and ash to meet government emissions standards initiated a period of explosive growth in the coal industry. Much of this growth occurred in the Northern Plains and Prairie Provinces in the form of more than twenty new mines, several with adjacent power plants.
Area mining, a type of surface mining used where coal seams are relatively horizontal and the surface terrain is nearly level, accounts for nearly all mining in the Great Plains. Area mining utilizes draglines to remove overburden, and the coal is then removed using power shovels and loaders. As each strip of overburden is removed, it is deposited as a spoil ridge in the area from which coal has already been excavated. Individual dragline cuts may be 100 to 200 feet wide and extend for thousands of feet. Several square miles may be excavated over the life of a mine.
Land productivity and water availability and quality are particularly significant issues in the semiarid range and farmlands of the Northern Great Plains, and mining companies are required to reclaim mined land. To ensure land productivity in mined areas, top-soil and subsoil are removed by scrapers and stockpiled prior to mining. Following mining, the spoil ridges are shaped in a manner reflecting the premining topography, the soil is replaced, and the sites are revegetated. The recontoured spoil density, initially about 25 percent greater than the original material, decreases over time to about 20 percent of the original material. Differential subsidence, with the potential for ponding, salinization, and disrupted cultivation, can be addressed in large part through materials placement and grading practices.
In the premining landscape, reducing conditions prevail at depths greater than thirty feet, but excavation brings these materials into contact with oxygen. As a result, recharge through spoil banks and newly reclaimed areas produces groundwater characterized by elevated concentrations of dissolved solids, elevated concentrations of sodium and sulfate, and increased alkalinity. In most areas, carbonates and hydroxides provide a high natural buffering capacity that precludes significant acid mine drainage. Surface and groundwater quality improves with time, but the disruption of groundwater flow resulting from the removal of the coal and the aquifers in the overburden cannot be fully remedied within the mined area.
In 1997 Great Plains coal production stood at 375 million tons from forty-eight mines, accounting for nearly 33 percent of the combined U.S.-Canadian output. The 337 million tons produced from the thirty-four mines in Wyoming, North Dakota, and Montana accounted for 78 percent of U.S. low-rank production, 31 percent of total U.S. production, and nearly 90 percent of total Great Plains production. The 36.5 million tons from the ten mines in the Prairie Provinces accounted for 42 percent of total Canadian production and 10 percent of total Great Plains production. New Mexico and Kansas contribute the remaining 1.6 million tons, or 0.4 percent, of Plains production. Mines in Montana and Wyoming are producing at only three-quarters of capacity. Most of the subbituminous coal mined in Wyoming and Montana is shipped out of state for use in coal-fired power plants. In contrast, the lignite of North Dakota and Saskatchewan is mainly utilized by mine-mouth power facilities.
In the Great Plains, 99 percent of coal production is from surface mines. The 85 billion tons in demonstrated surface-minable reserves in the Northern Plains states of the United States, including the 19 billion.ton reserve of the Wyodak seam in the Powder River Coal Region, are su.cient to last for nearly 250 years at current production levels and represent nearly half of the demonstrated surface mine reserves of the United States. Employment at Plains surface mines stood at approximately 7,200 workers in 1997. Productivity levels (tons of coal per miner per hour) for surface mines in 1997 in Wyoming (35.4), Montana (23.6), and North Dakota (17.8) were well above the U.S. surface mine average of 9.5, reflecting economies of scale and relatively low overburden to coal thickness ratios. Coal severance taxes are levied in all states with Plains-based coal production.
The Powder River Coal Region of northeastern Wyoming and southwestern Montana contains North America's thickest and most extensive low-sulfur coal seams, including the seventy-foot-thick Wyodak seam, and the region's 269 million–ton production accounts for 70 percent of Plains production and 23 percent of combined U.S.-Canadian production. Most of the coal is transported out of state, with over half going to just six states in 1997 (Texas, Missouri, Illinois, Oklahoma, Wisconsin, and Iowa). Most Powder River region coal is produced from federal lands.
Great Plains coal resources have also figured in unconventional types of coal-based energy and commodities. Since 1983 lignite from the Beulah-Zap seam in the Fort Union Coal Region has been the feedstock for the large-scale production of substitute natural gas at the Great Plains Coal Gasification Plant near Beulah, North Dakota. The Powder River and Raton Mesa Coal Regions are significant areas of coalbed methane exploration and development. Between 1972 and 1988, a variety of federal and private entities conducted field tests in Wyoming, including tests at two sites in the Powder River Coal Region, designed to evaluate the technical and environmental feasibility of underground coal gasification in low-rank coals. Weathered low-rank coal, known as Leonardite, has been used as an additive in drilling fluids and as a soil amendment. Coal combustion by-products such as fly ash and bottom ash have been used for concrete, engineered fills, aggregate, soil stabilization, and ceramics.
Daniel J. Daly University of North Dakota
Energy Information Administration. Coal Industry Annual 1997: U.S. Department of Energy. Energy Information Administration, December 1998.
Keystone Coal Industry Manual. Chicago: Intertec Publishing Company, 1998.
Wood, G. H., Jr., and W. V. Bour. Coal Map of North America. Washington DC: U.S. Geological Survey, 1998.