The single most damaging aspect of coal mining in relation to the Susquehanna River environmentally is acid mine drainage. The majority of acid mine drainage occurs from drainage discharge from a large network of abandoned underground mining tunnels.
Most deep mines are below the level of the local water table.
When in operation, pumping was necessary to keep water out of these mines. Once abandoned, these mines became flooded up to the level of the water table. With the absence of now excavated coal veins, the natural hydrological system of the water table in these areas have been disrupted, allowing for the unnatural favoring shift in the equilibrium of the lands geochemistry. Iron Pyrite is an abundant mineral present in most areas where coal veins are present. Once this and other minerals are exposed to water, the above reaction readily takes place.