Until the time of World War I, coal mining in Ohio was conducted almost exclusively underground and largely by manual labor.

These underground mining operations gained access to coal seams by vertical mine shafts of up to 200 feet deep, by horizontal mine entries (drift entries) cut into hillsides at the coal elevation, or by sloping tunnels angling downward from the ground surface. Early underground mines were small, discontinuous, and poorly mapped.

To maximize coal production, roof support was usually minimal. Further, coal pillars were often removed upon abandonment of the mines, making them highly prone to later subsidence.

With the advent of large, efficient excavating equipment, new drilling techniques, and newly developed explosives in the mining industry around World War II large earthmoving operations became possible. Surface mining operations thus became an economic alternative to underground mining. Surface mining involves excavation of all of the rock and soil (overburden) above the desired coal seam, exposing the coal seam at the surface. The excavated rock and soil, known as “mine spoil,” is placed in piles away from the excavation site. The exposed coal is removed in a way that includes as little non-coal rock as possible.

A very efficient recovery system of underground coal mining, known as longwall mining, was introduced into Ohio due to the development of automated mining equipment. The technique involves total removal of large blocks of coal which allows the overburden to collapse or subside in a controlled and predictable manner. This technique has significantly increased productivity and reduced costs so that underground mining can remain competitive with surface mining. It has the added benefit of allowing mitigation of subsidence impacts to occur while the mining company is still operating in the vicinity, rather than years after mining is complete.