In Kentucky, the Pennsylvanian Breathitt Formation, Hazard No. 7 coal seam was exposed in drift mouths, mine benches, and auger holes drilled during pre-reclamation-law underground and contour mining. Vapor from the LC fire reported in 2006, presumably started by spontaneous combustion, was visible and smelled at a nearby shopping center and environs, while burning threatened the stability of a public-water-supply tank. Ignited in 2006 by a forest fire, the RM fire is thought to currently be burning in abandoned-mining tunnels beneath Kentucky Route 80, a scenario for dangerous subsidence.
In Mulga, gob piles contain waste rock and coal from mining the Pennsylvanian Pottsville Formation underground. The gob has repeatedly ignited since the 1980s as a consequence of lightening strikes and people burning refuse on the piles. Cut-off trenches encircling the gob and burial beneath 0.5-1 m of compacted soil has extinguished some of the fires.
The Mulga Gob Fire can be smelled for several miles and has resulted in respiratory complaints, streams with a pH of 2-3, and an increase in the number of automobile accidents due to early-morning smoke combining with fog to reduce driving visibility.
Gas analyses revealed 47 compounds including the toxins toluene and xylene; greenhouse gases methane and carbon dioxide; and the potential ozone-forming gases ethene, ethane, propene, and propane, all emitted from gas vents (165-385oC) into the atmosphere. Surficial deposits include creosote, sulfur, and ammonia compounds, all potential soil and water pollutants.