We offer a guide to help the public and local officials further understand potential problems associated with previously mined areas.
Acid Mine Drainage
Acid mine drainage is the most severe and well-recognized environmental problem related to coal mining and can impact surface waters, including lakes, ponds, creeks, and even entire watersheds. AMD is water typically with a pH less than 4 that drains from mine workings and from mine spoils, and coal refuse (called acid rock drainage). The low pH is due to the formation of acid resulting from the oxidation of sulfide minerals (e.g., pyrite) in the host rock as it is exposed to air and water during mining. The acidic water solubilizes moderate to high concentrations of metals from the rock and sulfate. When a watershed has been heavily mined, AMD can constitute the majority of water in the receiving surface waters. These water bodies can have pH values between 2.0 and 5.0 and contain hundreds of milligrams per liter (mg/L) of acidity and dissolved iron. Water bodies impacted this severely are usually devoid of fish and other aquatic organisms. Only a very limited number of animal and plant species can survive under these conditions. Hundreds of projects have been performed in an attempt to evaluate and reclaim some of these watersheds and return them to healthy aquatic habitats. Remediating AMD in a watershed can be extremely difficult. Many times there is no at-source AMD abatement technique that is feasible or cost-effective. In these cases, treatment of the AMD is sometimes the only alternative for improving water quality and aquatic habitats in the receiving water bodies.
Erosion of mine spoils and coal refuse caused by stormwater runoff can be a problem, especially in the eastern and central United States where severe rainstorms can occur. Erosion occurs because the piles of mine spoils and coal refuse are often loose, unconsolidated, steep-sloped, and un-vegetated. Transported sediments enter surrounding drainage channels, creeks, streams, and reservoirs, and clogged stream channels can subsequently cause flooding. Heavy sediment loads can coat streambeds and have a profound impact on fish and other aquatic animals.
Open dumping or “midnight dumping” is the illegal disposal of municipal and industrial wastes and is common at abandoned mine sites. People looking to avoid the costs or inconvenience of legal dumping often dispose of their wastes in an abandoned pit or mine shaft causing additional contamination concerns.
Old air shafts or vertical entries of underground mines may result in falls, especially when located in woods, partially covered, and not readily visible. These shafts and open workings can be hundreds of feet deep. If not sealed, drift entrances into underground mines can also pose serious risks as old timbers and roof rock of these drifts can be very unstable and subject to collapse. Hunters and hikers sometimes seek refuge from bad weather in these entrances, and children may enter simply to hide or play.
Subsidence of the ground surface occurs when it slowly sinks or collapses into underground mine openings below. Underground mines may have vertical shafts, slopes, drift openings, mine workings (including haulage ways, water and drainage tunnels), and other passageways excavated from the subsurface that may cause subsidence. Buildings and other structures constructed on land undergoing active subsidence can crack, shift, tilt, and split. Damage to buildings can be so severe that they must be abandoned and demolished.