In many rural Appalachian regions, the coal mining
industry has been a source of constant employment for several
years. Unfortunately, the mining industry has also been a source
of pollution and environmental degradation. One of the largest
pollution issues facing many mining areas today is Acid Mine
Drainage.
Nonpoint source pollution is the nation's biggest threat to water quality; Acid Mine Drainage (AMD) from abandoned mines is the largest nonpoint source pollution problem affecting streams and rivers in the Appalachian region of the United States. AMD is a major concern of both the mining industry and the general public due to its degrading effects on ground and surface water.
Acid Mine Drainage is particularly a problem in poor rural areas because of costly remediation techniques. Coal companies are not always responsible for complete remediation of mine sites and many communities are too poor to absorb the clean-up costs. In many cases, the mines are simply abandoned.
Dr. Carl Zipper, Virginia Polytechnic Institute and State University, on Acid Mine Drainage.
A study by Epps (1978) reports that in many coal mining regions, groundwater supplies sufficient for private use are mainly located in the upper few hundred feet of bedrock. Because the groundwater is located so close to the land surface, the water supply is especially susceptible to pollution from percolation.
Groundwater quality in many of these areas is fair to poor due to high levels of iron, sulfur, sodium chloride, and natural gas. Both the quality and quantity of groundwater decrease with depth, and in some areas, mining activities have depleted groundwater resources altogether. To assure adequate water supplies in the future, long-term solutions must be developed to protect the already insufficient groundwater supplies from pollution, such as AMD.
Acid Mine Drainage is also detrimental to surface waters. In many coal mining regions, surface waters are polluted by direct AMD runoff, as well as by polluted groundwater. Notice the orange and green runoff in the two pictures below. Both pictures illustrate surface water pollution by AMD. Surface waters polluted by AMD have a negative impact on aquatic populations. The impact on fisheries has been studied extensively by the EPA.
Pictures provided by Justin Babendreier, used with permission
rainageHutchinson and Ellison (1994) use the term AMD to describe leachate, seepage, or drainage that has been affected by the natural oxidation of sulfide minerals contained in rock which is exposed to air and water. The oxidation reactions responsible for the formation of AMD are often accelerated by biological activity. These reactions yield low pH water that has the potential to mobilize heavy metals that may be contained in the exposed geologic materials. AMD can have detrimental impacts on the quality of the ground or surface water into which it discharges.
When acidic water travels through the fractures and fissures of carbonate rocks, the calcium carbonate, which is insoluble in water of higher pH, is dissolved to form calcium bicarbonate, which is soluble in water. The calcium bicarbonate will then form an equilibrium with free calcium and carbonic acid. The result of this chemical reaction is hard water.
Although AMD is a natural biological process, the reaction rarely, if ever, occurs naturally. The process is often accelerated by human activities such as coal mining because mining exposes the pyrite to both water and air. When pyrite (FeS2), found in coal seams and overlying rock, is exposed to air and water, as it is during the mining process, sulfuric acid is produced. To the left is a picture illustrating AMD from an abandoned mine site. Notice the rust color which is indicative of AMD. The following oxidation and reduction reactions illustrate the breakdown of pyrite that leads to AMD:
1) FeS2 + 7/2O2 + H2O
Fe2+
+ 2SO42- + 2H+
2) Fe2+ + 1/4O2 +H+
Fe3+ + 1/2H2O
3) Fe3+ + 3H2O Fe(OH)3 +
3H+
4) FeS23+ + H2O 15Fe2+ +
2SO42- + 16H+
Sulfuric acid then dissolves heavy metals, such as lead, zinc, copper, and mercury, and allows them to enter the groundwater system. Lead and mercury are of particular concern when dissolved in groundwater because they are extremely toxic to humans.
The Department of Environmental Protection cannot issue a
permit for new coal mining where it is determined that the mining
will cause AMD. This regulation prevents new AMD development, but
unfortunately, many mines have been in operation for generations
and the permits are not required. 
In
addition, there are many abandoned sites with expired permits
which produce large amounts of AMD. Many times it is more cost
effective for companies to pay the fine imposed rather than to
remediate the problem.
The previous picture was taken at Dominion Coal Corporation Mine number 7. Notice in the picture to the left, the mining permit expired in December, 1993.
AMD can develop throughout the mining process: underground workings, waste rock dumps, open pit mine fractures, tailing deposits, ore stockpiles, etc. Unfortunately, once AMD occurs, it is virtually impossible to reverse the negative effects because of high clean-up costs and a lack of available technology.
Loopholes in the permitting
process for coal mines allow some mines to be abandoned without
remediation or fines. Unfortunately, pollution from abandoned
sites often goes untreated because many local governments do not
have the financial means to remediate the sites. The picture to
the left as well as the picture below were taken at Dominion Coal
Corp. Mine No. 7. Recall that the mining permit for this
operation expired December, 1993. In the picture to the left,
just below the white building, you can see the mine drainage
which is shown as a close-up in a previous picture.
The potential solutions to AMD only treat water at the surface to further prevent groundwater contamination. To date, there is no proven way to remediate already polluted groundwater. Traditional methods of groundwater remediation are not practical for treating water contaminated by.html">West Virginia University, in Morgantown, are currently developing alternatives to treating AMD with chemicals. Inexpensive techniques for treating AMD will help the areas where no one person or company is responsible for the pollution. Options range from wetland anoxic limestone drains to open limestone channels. Anoxic drains are very effective if the iron is predominantly in the reduced form and there is a low dissolved oxygen and aluminum content in the water. Open limestone channels are created by filling drains or stream beds with high quality limestone and have been shown to reduce the acid and metal content produced by AMD by 25-40%.
Singh (1992) attempted to treat acid mine drainage by biological sulfate reduction. Bacteria which reduce sulfate to sulfide are added to surface waters, and the following processes occur:
1) 2CH2O (bacteria) + SO42- H2S
+ 2HCO3-
2) H2S + M2+ MS + 2H+
3) HCO3- + H+ H2CO3
Equation (1) represents the reduction of sulfate to sulfide by the bacteria. The sulfide will then combine with heavy metals to produce metal sulfides as demonstrated by equation (2). These metal sulfides will then settle out of the stream. This process also produces acidity, but that is counteracted by the process in equation (3) which takes up acidity. If the bacteria produce sulfide in excess of what is needed to precipitate all the metals, acidity is still reduced according to equation (3), however since equation (2) no longer occurs, there is excess sulfide being released by the process. Sulfide is toxic to aquatic life, has a foul odor, and has the potential to oxidize back to sulfate. This process has the potential to reduce some effects of AMD, but also has the potential to create more problems.
The potential solutions to AMD only treat water at the surface to further prevent groundwater contamination. To date, there is no proven way to remediate already polluted groundwater. Traditional methods of groundwater remediation are not practical for treating water contaminated by AMD because treatment processes clean the polluted water, but do nothing to prevent further degradation. The only effective way to control pollution from AMD is to stop the process before it takes place.
In many rural areas groundwater is the major source of water for commercial and private use, water contamination is of great concern. If contaminated waters cannot be treated and pollution continues to take place, clean water supplies may be unavailable to meet increasing demands in the near future.
Student authors: Amy E. Meadows and Amanda A. Carpenter
Faculty Advisor: Daniel Gallagher, dang@vt.edu
Copyright © 1998 Daniel Gallagher
Last Modified: June 7, 1998
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