On both a state and national scale, mine openings and tunnels are the most frequently encountered AML problems. When many older underground mines were abandoned, the entries into them were not adequately sealed. Unstable or open portals and shafts on the ground surface can be very hazardous. Dangers within the mines include poisonous or explosive gases, oxygen deficiencies, flooded sections, unstable roofs, hard-to-see vertical shafts, venomous insects, poisonous snakes and disorienting mazes of mine workings. These problems are compounded by total darkness within underground mines.
Abandoned mines are nothing like naturally formed caves which are attractive to recreational and professional explorers, and should never be mistaken for caves. Old mines and shafts conceal a multitude of potentially lethal hazards. Each year, a number of people are killed or injured nationally in abandoned mines. The safest thing to do is to stay completely out of them.
Spoil banks from surface mines, coal waste piles, and natural slopes at abandoned mines sometimes become unstable. The most common causes of landslides include the following: steep slopes; saturation of slopes by water from underground mines, surface mine pits, or natural aquifers; and the inherent instability of the disturbed materials. Landslides can damage roads and buildings, and can block paths of streams, causing upstream flooding.
Highwalls are created during surface mining as sides of hills are removed to expose coal seams. Rock faces resembling cliffs remain at the point where the mining excavation ceased. Before stricter reclamation laws were passed, miners were not required to backfill mine spoil against highwalls. Thus, there are many miles of highwall remaining in Ohio. Typically, they range in height from 20 feet to 100 feet. The degree to which they pose a danger to the public is determined by proximity to human dwellings or activities and to public roads; stability; and heights and angles.
Erosion and sedimentation from AML lands often cause flooding problems by clogging stream channels and culverts. Extensive amounts of reclamation have been done to eliminate AML sediment sources in southern and eastern Ohio.
Acid Mine Drainage (AMD)
Rock layers associated with the coal seam sometimes contain iron sulfide minerals, with pyrite the most common. Sulfur-bearing materials exposed to air and water during mining react with oxygen and water to form dilute solutions of sulfuric acid which may also contain a number of other dissolved minerals. This contaminated water, referred to as acid mine drainage (AMD), often seeps from underground mines and sometimes from surface mined areas. AMD is a significant environmental problem associated with abandoned mined lands and is often very difficult to control. Over 1300 miles of Ohio streams are impacted by AMD.
Ohio has an AMD set-aside program that authorizes up to ten percent of its annual AML allocation to be placed in an interest bearing fund which is used to conduct AMD abatement projects in targeted watersheds.
More than two billion tons of coal have been removed from underground mines in Ohio since the 1800's. In the early days, many mines were never surveyed. Thus, no maps exist to describe the extent of abandoned underground mines. Geologists estimate that up to 600,000 acres are underlain by 4,600 abandoned underground mines in the 30 coal producing counties in Ohio.
Mine subsidence is also a common problem caused by abandoned underground mines. Projects are often undertaken to fill in and stabilize the mines most likely to cause subsidence damage.
When buildings are constructed above mines, major damage to walls and foundations can occur if the mine subsides. Most insurance policies do not automatically cover mine subsidence damage to your home. See Mine Subsidence Insurance.