Sources of Coal Mine Methane
Coal mine methane (CMM) refers to methane released from the coal and surrounding rock strata due to mining activities. In underground mines it can create an explosive hazard to coal miners so it is removed through ventilation systems. In some instances, it is necessary to supplement the ventilation with a degasification system consisting of a network of boreholes and gas pipelines. In abandoned and surface mines, methane might also escape to the atmosphere through natural fissures or other diffuse sources.
CMM is emitted from five sources:
- Degasification systems at underground coal mines (also commonly referred to as drainage systems). These systems may employ vertical and/or horizontal wells to recover methane in advance of mining activities (known as "pre-mine drainage") or after mining activities (in "gob" or "goaf" wells).
- Ventilation air from underground mines, which contains dilute concentrations of methane.
- Abandoned, or closed, mines, from which methane may seep out through vent holes or through fissures or cracks in the ground.
- Surface mines, from which methane in coal seams is directly exposed to the atmosphere.
- Fugitive emissions from post-mining operations, in which coal continues to emit methane as it is stored in piles and transported.
EPA's Greenhouse Gas Reporting Program (GHGRP) collects information from all underground coal mines that liberate 36,500,000 actual cubic feet of methane or more per year. Surface mines and abandoned mines do not report to the GHGRP. In 2019, GHGRP reporters reported 34,206,291 metric tons of carbon dioxide equivalent (CO2e). See GHGRP trends from the underground coal mines sector.
CMOP provides resources for understanding and reducing methane emission from different types of sources. Resources by CMM source type are available here: