Coal, Coal Mines, and Mine Subsidence
What do the names Essen, Summer Hill, Nixon, Harrison, and Mansfield have in common? Answer: They are all names of coal mines under Mt. Lebanon that were run by the Pittsburgh Coal Company in the early 1900’s. Mining in Allegheny County began in 1759 when British soldiers mined coal from the Pittsburgh bed at the base of Mount Washington. Since then, millions of tons of bituminous coal have been mined from under much of the county, including Mt. Lebanon. The most prolific coal seam is called the Pittsburgh Coal, which averages 5 to 8 feet thick, but locally may be up to 12 feet thick. In particular, an area just south of Painters Run has abnormally thick coal that was deposited in a depression in the ancient coal swamp. The miners called this area the ‘Panhandle Trench.’ The Pittsburgh Coal outcrops locally (see figure) along Painters Run, near Jim Jenkins garden center; along the hillside near Route 50 from Heidelberg to Bridgeville; and along Route 88 north of Castle Shannon. Many of these areas had mine openings and railroads to move the coal. An old railroad grade may still be seen along Painters Run Road.
Today, all of the mines under Mt. Lebanon are abandoned. This provides the potential for a mine subsidence. When collapse occurs, structural damage may result to buildings on the surface. The potential damage zone may extend outward from the actual mine collapse zone because the rock support structure is weakened. One of the greatest factors determining the risk of damage from mine collapse is the height of the rock above the mine, the overburden. If the overburden is less than 100 feet, the risk of subsidence is high. If the overburden is greater than 200 feet, the risk is low.
The accompanying figure shows the overburdens in the Mt. Lebanon area. It is meant to be a guide only. In general, most of Mt. Lebanon has overburdens greater than 200 feet. However, there are several areas that are at high risk of mine subsidence damage. One area is along Painters Run Road and along the southern part of Cedar Boulevard. Here, overburdens are generally less than 100 feet. Another area is along Route 88, north of Castle Shannon, where overburdens are less than 100 feet. Finally, the valleys containing Scrubgrass Road and Greentree Road in Scott Township have low overburdens.
The Pennsylvania Department of Environmental Protection in McMurry (724-941-7100) can evaluate your property and determine if mine subsidence insurance is warranted.