Methane Emissions from Abandoned Coal Mines
IES was recently involved in a stray gas case in Kentucky where air with elevated methane and carbon dioxide concentrations migrated into residential homes.
Methane concentrations exceeded the lower explosive limit (LEL) and represented a threat to nearby residents.
IES determined from stable isotopes and careful mapping of nearby mined lands that the stray “air” came from an abandoned deep coal mine.
The coal mine was dug below the water table but was kept dry by water pumps during operation. The pumps were shut off when the mine was abandoned, and the mine then flooded with groundwater.
Flooding created a hydraulic piston-like action that forced the coal mine atmospheric air and coal bed methane into water wells and basements.
Abandoned Coal Mine Emissions
According to the United States Environmental Protection Agency (USEPA), abandoned mine methane (AMM) is responsible for 5 to 10 percent of US methane emissions associated with coal mining. Surface mines vent little methane after abandonment. But, deep underground mines continue to vent methane until the mine floods.
The USEPA tracks over 1,000 abandoned deep coal mines; however, the exact number of abandoned deep coal mines is unknown. Estimates range from 46,000 to over 500,000 mines.
Some operators voluntarily manage methane emissions because it is good business. In some states, government regulations require methane management at operating coal mines but little is being done to seal legacy deep coal mines as a way to reduce overall greenhouse gas emissions, which can continue for many years later—a yet unquantified part of methane emissions to the atmosphere.
For more information about natural methane in groundwater and the environment we have published the following Briefings:
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