Filling mines with the residues of coal combustion is a viable way to dispose of these materials, provided they are placed so as to avoid adverse health and environmental effects, says a new congressionally mandated report from the National Academies' National Research Council. The residues left after coal is burned to generate power -- often referred to as coal ash -- consist of noncombustible coal matter and material trapped by pollution control devices. Enforceable federal standards are needed to guide the placement of coal ash in mines to minimize health and environmental risks, the report says.
Coal combustion in the United States leaves behind enough residue to fill 1 million railroad coal cars each year, and the volume continues to grow along with rising energy demands and improved pollution-control measures. Most of this ash is disposed of in landfills and surface impoundments, but it is increasingly being used in mine reclamation. In addition, about 38 percent of the residues are currently used to make cement, wall board, and other products. The report encourages the continued use of some residues in industrial applications as a way to reduce the amount requiring disposal.
"Because the amount of coal combustion residues is large and increasing, we should pursue productive uses for them," said Perry Hagenstein, chair of the committee that wrote the report and president of the Institute for Forest Analysis, Planning, and Policy, Wayland, Mass. "When such uses are not feasible, putting residues in mines as part of reclamation provides an alternative to landfills and surface impoundments, although potential health and environmental risks must be addressed."
Returning coal combustion residues to mines has certain advantages, the committee said. For example, the residues provide filler for mine reclamation efforts that restore land use conditions at a site, and putting these residues in mines lessens the need for new landfills. The residues may also neutralize acid mine drainage, lessening the potential for some contaminants from mines to enter the environment.
Little is known about the potential for minefilling to adversely impact groundwater and surface water, particularly over long time periods. Because information from minefilling sites is limited, the committee assessed potential risks by examining data on adverse environmental effects from surface impoundments and landfill sites. The data indicate that adverse environmental impacts can occur when coal ash containing toxic chemicals has contact with water or when the residues are not properly covered. The report recommends that minefills be designed so that movement of water through residues is minimized.
To aid understanding of risks and limit the potential for adverse effects, the committee recommends improved characterization of coal combustion residues before they are placed into mines. This would involve understanding the composition of the residues and testing the potential for hazardous chemicals to leach into the environment under all possible conditions in the target mine, particularly with respect to various pH levels. Mine sites also must be well-characterized, which includes developing a clear understanding of groundwater flow patterns.
The report also recommends a more robust program to monitor mine sites where coal residues have been placed. Currently monitoring involves testing water in wells placed around the mine sites. However, the number and placement of wells is generally inadequate, according to the committee. It suggested taking several factors into account -- such as rates of groundwater flow and estimated risks from contamination -- to place wells in a manner that yields early data on potential water contamination.
Under the federal Surface Mining Control and Reclamation Act, states are generally responsible for broadly regulating the management of coal combustion residues during mine reclamation. While general enough to cover putting residues in mines, SMCRA does not specifically regulate the practice, leading some states to say they lack the power for more explicit regulation. The report says that development of enforceable federal standards would give the states such authority, while allowing sufficient flexibility for adapting requirements to local conditions. Only through enforceable standards can minimum levels of protection be guaranteed nationally, the committee added.
The study was sponsored by the U.S. Environmental Protection Agency. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter. A committee roster follows.
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