Coal mining began over 200 years ago in Pennsylvania. Today, there are more than 1 million homes that sit above abandoned mines. Because of this, Pennsylvania has one of the largest abandoned mine problems in the country.
According to the Department of Environmental Protection (DEP), mine subsidence is “defined as movement of the ground surface as a result of readjustments of the overburden due to collapse or failure of underground mine workings.” Mine subsidence usually presents itself on the surface in the form of either sinkholes or troughs. These impacts usually take many years to present themselves.
Sinkholes are generally only associated with abandoned mine workings, particularly shallow room-and-pillar mines where there is less than 50 feet between the coal seam and the surface. Room-and-pillar mining involves cutting into the coal seam in square or rectangular blocks, which are the pillars. The pillars support the ground above the seam. The openings between the pillars are the rooms. Sinkhole subsidence typically occurs when the mine roof collapses into a room of the room-and-pillar mine causing the overlying ground to cave in. This caving in creates a depression in the ground surface. Deeper mines often fill in when they collapse, and the subsidence never makes it to the surface. Today, shallow mines are not generally allowed. Mines now have to be at least 100 feet below the ground surface and/or any structures. More shallow mines may be authorized by the DEP only if the coal company has a subsidence control plan that shows that the mine will be stable.
Troughs can occur over active or abandoned mines. What triggers a subsidence trough is very different from a sinkhole, even though the resulting impacts to the surface may be similar. Troughs usually occur when the mine pillars “punch” into the mine floor or roof which causes the above ground to sag downward.
The state is responsible for “shoring up mine subsidence” caused by abandoned coal mines. Under the authority of the federal Surface Mining Control and Reclamation Act of 1977 (SMCRA), the PA Bureau of Abandoned Mine Reclamation is responsible for taking care of subsidence problems among other issues caused by mining. The SMCRA calls for a federal tax on coal mining, which is distributed among the states to help pay for abandoned mine reclamation. This tax is set to expire in seven years. Before the tax expires, Pennsylvania will receive between $750 million and $770 million of those tax dollars for mine reclamation. Statewide, though, it is estimated that it would cost $4.7 billion to fix all of the known problems with abandoned coal mines. This amount does not include emergency projects, such as when a subsidence causes a road to sink.
The state, however, is not responsible for damage caused to private property. Many people are not prepared for mine subsidence. Of the more than 1 million homeowners who are sitting on top of abandoned mines in Pennsylvania, only about 6 percent have subsidence insurance. Most of those who do have insurance are in Southwestern Pennsylvania. Mine Subsidence Insurance through the Commonwealth of Pennsylvania is $57.50 per year for $100,000 worth of coverage up to $500,000. Standard homeowner’s insurance does not cover damage caused by subsidence.