Coal Mining and Pollution

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Coal is recovered from the ground either by underground or surface mining. Underground mining creates voids over many square miles. Two basically different methods are used: longwall and room-and-pillar mining. In longwall mining all coal is recovered from the mined panels; hence, subsidence occurs at the surface almost immediately and it is planned for. Room-and-pillar mining leaves about half of the coal in the ground as pillars to support the surface and prevent subsidence. However, subsidence may still occur because coal pillars or the floor strata under them fail, sometimes decades after mining (this sort of unplanned subsidence is a significant problem in major coal-producing states of the past). Subsidence causes damage to structures and interferes with the drainage of surface water; it may also impact aquifers. Coal left in the ground may catch fire, for example, through spontaneous combustion. Mine fires are difficult to control; some have burned for decades, even centuries. They can cause considerable local pollution, as well as other problems. Coal also always contains methane (CH4), most of which is released into the atmosphere during mining. On the average, the deeper a mine, the more methane it generates. Methane is a very potent greenhouse gas and contributes to global warming. Another significant environmental problem is related to underground mines that operated above the local drainage level. The mine workings collect and conduct water that oxidizes the ever-present pyrite (FeS2) in coal-bearing strata and causes acid mine drainage into the local drainage system. This is a common problem in the mountainous Appalachian coal fields where many old mines were operated at shallow depth above valley floors.

For surface mining, large machines are used to remove all rocks and/or soil above the coal bed or beds to gain access to it or them (usually at depths of less than 150 to two hundred feet). Any surface drainage and aquifers in the overburden will be severely impacted within the vicinity of the mine pit. Also, the fertility of agricultural land becomes a concern. Modern mining laws require the careful monitoring of groundwater at mines and the restoration of proper drainage and fertility to farmland, to its premining levels, through reclamation. Contaminated water (e.g., water containing suspended fine solids and/or dissolved minerals) may run off the open pit and must be treated before release into the local drainage system.

Modern mining laws seek to remedy or minimize the above-mentioned environmental and other problems related to the mining and cleaning of coal, as well as many other related concerns. See the table for a listing of the top producers of coal by state.

subsidence sinking of earth surface due to underground collapse mine workings the parts of a quarry or mine that is being excavated overburden rock and soil cleared away before mining reclamation in recycling: restoration of materials found in the waste stream to a beneficial use which may be for purposes other than the original use

LEADING COAL-

PRODUCING STATES

OF

THE

UNITED STATES

2001

Rank

State

Production

1

Wyoming

365.6

2

West Virginia

160.4

3

Kentucky

132.6

4

Pennsylvania

76.4

5

Texas

45.0

6

Montana

39.1

7

Indiana

37.1

8

Illinois

33.8

9

Colorado

33.4

10

Virginia

32.5

11

North Dakota

30.5

12

New Mexico

29.6

13

Utah

27.0

14

Ohio

25.3

15

Alabama

19.2

16

Arizona

13.4

Other states

20.4

U.S.A.

1,121.3

source: Adapted from U.S. Department of Energy.

coke carbon fuel, typically derived from bituminous coal, used in blast furnaces for the conversion of iron ore into iron coke carbon fuel, typically derived from bituminous coal, used in blast furnaces for the conversion of iron ore into iron scrubber an air pollution device that uses a spray of water or reactant or a dry process to trap pollutants in emissions

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