Problem: Coal Mining in the Lower Allegheny
The Allegheny Watershed has had a long history with coal mining within its boundaries. In particular, the Lower Allegheny is located in the center of a large field of high-volatile bituminous coal, as seen in figure below. It is this coal reserve that actually helped initiate development in the region during the industrial revolution. Coal mining activities continued into the twentieth century and are ongoing as surface mining (Pennsylvania Environmental Council, 2011).
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| (Pennsylvania Environmental Council, 2011). |
In surface mines, large, earth moving vehicles are set to move soil and rocks layer by layer in order to reach the coal seam. This activity disturbs landscapes, habitats, and soil quality as the earth’s surface is displaced (Pennsylvania Environmental Council, 2011).
The main concern for coal mining, for both underground and surface mines, is a byproduct of the mining activities known as acid mine drainage (AMD). This consequence of coal mining is caused by a natural oxidation process of iron sulfide containing materials, mainly pyrite. The pyrite, located both within the coal seam and surrounding rock materials, such as shale and sandstone, becomes exposed to the air during mining. When it rains or when water is used in the mining process, the pyrite becomes oxidized and forms new, water soluble chemicals known as ferrous sulfate, ferric sulfate, ferric hydroxide, and sulfuric acid. These chemicals can runoff into nearby streams as well as percolate into the groundwater where secondary reactions may occur with surrounding rock and mine spoil. These secondary reactions release minerals from the rock in high concentrations, including aluminum, zinc, and manganese, as well as iron oxide and aluminum oxide precipitates, further exacerbating the presence of acidic water (United States of America, 2000).
There is a natural threshold in which acid can be neutralized with sufficient alkalinity, so in some cases, AMD could be short-lived. However, when the threshold is surpassed, AMD begins to take a toll on the streams and rivers it flows into. Acid has the potential to greatly reduce the river’s pH, sometimes as low as pH 3.0. At these pH levels, large-scale fish kills are possible, such as occurred 1906 below the Kiskiminetas River within the Allegheny Watershed. In addition to increased acidity, precipitates, usually orange or yellow in color, sink to the stream bed, completely covering benthic habitats causing toxicity for algaes, fish, and invertebrates through ingestion. Besides affecting food supplies, precipitates can also clog the gills of invertebrates and fish, smothering them (United States of America, 2000).
Solutions
Reclaiming mine sites can be costly. For instance, much of acid mine drainage in the Allegheny originates from abandoned mine shafts that may not be properly closed, if closed at all. In 2000, the estimated costs of AMD clean up at these abandoned mine shafts were at $5 billion. Reclaiming all abandoned mine-land sites in Pennsylvania were estimated at $15 billion. This is because must be neutralized and chemicals are needed to do so. Furthermore AMD is still produced even after the mining has stopped because of the exposure of the sulfide containing rocks. Under the Surface Mining Control and Reclamation Act of 1977 as well as the Clean Water Act of 1972, mine operators are required to regulate their mining discharges through permits of allowable discharge levels. Should AMD occur, then the operators are responsible to create and implement a treatment plan to neutralize the acid and/or precipitate the dangerous metal ions. Table __ shows a list of 6 common chemical compounds used in AMD treatment.
Common Name | Chemical Name | Formula | Neutralization Efficiency |
Limestone | Calcium carbonate | CaCO3 | 30% |
Hydrated Lime | Calcium hydroxide | Ca(OH)2 | 90% |
Pebble Quicklime | Calcium oxide | CaO | 90% |
Soda Ash | Sodium carbonate | Na2CO3 | 60% |
Caustic Soda (solid) | Sodium hydroxide | NaOH | 100% |
20% Liquid Caustic | Sodium hydroxide | NaOH | 100% |
50% Liquid Caustic | Sodium hydroxide | NaOH | 100% |
Ammonia | Anhydrous ammonia | NH3 | 100% |
(Skousen et al., 1996)
Reclamation efforts are federally funded and distributed to states with approved reclamation plans through mining taxes at 31.5 cents per ton of surface mined coal, 15 cents per ton of underground mined coal, and 10 cents per ton of lignite. Pennsylvania’s Mine Reclamation plan has addresses watersheds and prioritizes watersheds through potential of water quality improvement, other funding sources, loss or contamination of domestic water supplies, and public health and safety. Goals for water treatment include AMD abatement, water supply/pipe replacement to ensure potable drinking water, and minimizing physical mine hazards (Pennsylvania Department of Environmental Protection, 2000).)
Recommendation 1:
In order to reclaim abandoned mine sites, reclamation plans, perhaps at the subwatershed level, must be established and submitted for funding. Outside funding sources should also be applied for.
Recommendation 2:
Planting of native herbaceous and tree species on surface mine sites could help reestablish the lost soil structure as well as improve the landscape.
