 quality, as it can become more brackish with increased sulfate levels.
- disruption of ecosystems and loss of stream and wetland functions.
- shock waves on the surface.
According to the Center for Public Integrity's study of southwestern Pennsylvania, the following damages have occurred:
- Due to subsidence, homes suffer shattered foundations, crooked roofs, and cracked plaster. As of September, 2008, 1,819 property owners had reported longwall damages since the state of Pennsylvania began documenting such complaints.
- Longwall is permanently lowering the area’s water table and draining its aquifers; state regulators have reported damages to 23 stretches over 97 miles of mined streams.
There is still the possibility of coal mining accidents, as roofs can collapse, and the process of longwall mining stirs up harmful coal dust and explosive methane, thought to be the cause of the explosion at Massey Energy's Upper Big Branch Mine in April 2010, which killed 29 miners.
How much land is disturbed by longwall mining?
Estimate for 2009: 13,235 acres
Background and calculations:
Longwall mining, a form of underground mining designed to completely remove underground coal seams, results in land subsidence over large areas. As documented by reports describing subsidence impacts in Pennsylvania and elsewhere, longwall mining produces serious impacts to buildings, surface water supplies, aquifers. In 2009, longwall mining accounted for 166.4 million tons of coal, or 50% of U.S. underground coal production. This included 101.2 million tons in Appalachia, 12.2 million tons in the Illinois basin, and 53.1 million tons in the West. According to the Energy Information Administration, longwall mine seam heights average 71 inches in Appalachia, 86 inches in the Illinois Basin, and 127 inches in the West. Assuming 1800 tons of recoverable coal per acre foot, the amount of surface area affected by longwall mining in 2009 was 13,235 acres.
TABLE 4: Longwall coal production, area disturbed, and land intensity by region (2009)
|Region||Production (million tons)||Average seam (inches)||Acres annually disturbed||Acres per million tons|
Sources: "Underground production by state and mining method, 2009," Energy Information Administration; "Longwall Mining," Table 4: Average Mining Height of Longwall Units, by State and Region, Energy Information Administration, DOE/EIA-TR-0588, March 1995. Note: Appalachia includes Alabama, Eastern Kentucky, Maryland, Ohio, Pennsylvania, Virginia, and West Virginia. Illinois Basin includes Illinois and Wesetrn Kentucky. West includes Colorado, New Mexico, Utah, and Wyoming.
Global longwall production
World coal production in 2009 is estimated at 5,990 million metric tons (5,348 million short tons) for hard coal and 913 million metric tons (815 million short tons) for brown or lignite coal. Worldwide, approximately half of coal production is produced via longwall mining, mainly due to the high proportion of Chinese mining performed using longwall methods. In China, underground mining accounted for 85.9% of total production in 2008. There are more than 20 underground coal mining methods in China, almost exclusively longwall. Applied to estimated 2009 production of 3,210 million short tons, the total amount of coal produced via longwall mining in China is 2,757 million short tons. In 2008, China's 268 national strategic mines operated 1,545 longwall faces and 4,808 development faces. Of these, 88.3% are mechanized.
Other countries with major amounts of longwall mining include:
- United States: The United States operates 49 longwalls producing over 175 million metric tons (156 million short tons) per year.
- Australia: China has 29 operating longwall faces producing 47.5 million tonnes (42.4 million short tons)
Longwall mining in Illinois
Mining companies are buying up land in Illinois from struggling farmers for longwall mining. In Litchfield, IL, Cline Mining Corp. began buying land, prepping the ground for mining but leaving it unusable. Removing the slabs after mining can lead to sinking on the surface, with som