Understanding Coal Ash and the New Final Rule—Part 1
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The makeup of coal ash: Coal ash is essentially the byproduct of the combustion of coal at power plants that contains contaminants like mercury, cadmium, and arsenic associated with cancer and various other serious human health effects. Coal ash is disposed of in wet form in large surface impoundments and in dry form in landfills, and the EPA says there are several different types of materials produced in the processes, including:
- Fly Ash is produced from burning finely ground coal in a boiler and is a very fine, powdery material composed mostly of silica;
- Bottom Ash is made up of the coarse angular ash particles that are too large to be carried up the smoke stacks, and this ash remains in the bottom of the coal furnace;
- Boiler Slag is molten bottom ash from slag tap and cyclone type furnaces that turns into smooth glassy pellets after cooling with water; and
- Flue Gas Desulfurization Material (FGD) is the material leftover from the process of reducing sulfur dioxide emissions from a coal-fired boiler. It can be a wet calcium sulfite or calcium sulfate sludge or a dry, powered mixture of sulfites and sulfates.
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The volume of U.S. coal ash produced and disposed of annually. According to the EPA, coal ash “is one of the largest industrial waste streams generated in the United States. In 2012, more than 470 coal-fired electric utilities burned over 800 million tons of coal, generating approximately 110 million tons of CCRs in 47 states and Puerto Rico.” In addition, the EPA says, “In 2012, approximately 40 percent of the CCRs generated were beneficially used, with the remaining 60 percent disposed in surface impoundments and landfills. Of that 60 percent, approximately 80 percent was disposed in on-site disposal units.” More than 310 active on-site landfills now receive coal ash with the average size of more than 120 acres and an average depth of over 40 feet. An additional 735-plus active on-site surface impoundments that average more than 50 acres in size with an average depth of 20 feet are also in use.
The impetus for the new rule: Although coal ash has been a product of electricity generation for decades, a 2008 coal ash spill in Kingston, Tennessee, brought the problem of safe management to the national forefront. According to the EPA, the incident occurred at the Tennessee Valley Authority (TVA) power plant when an ash disposal cell failed, releasing “an estimated 5.4 million cubic yards of fly ash to the Emory and Clinch Rivers and surrounding areas. The release extended over approximately 300 acres outside the ash storage area.” When released, the EPA says the initial “wave” of water and ash “destroyed three homes, disrupted electrical power, ruptured a natural gas line in a neighborhood located adjacent to the plant, covered a railway and roadways in the area, and necessitated the evacuation of a nearby neighborhood.”
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How the EPA evaluated coal ash storage and disposal nationwide. EPA’s Coal Ash Surface Impoundment Integrity Assessment Program assessed all of the nation’s aboveground coal ash surface impoundments, which was more than 500 units at more than 200 power plants. By its conclusion in 2012, the program was “one of the largest targeted field assessments ever conducted by EPA.”
The structural integrity reports produced were “completed by contractors who are experts in the area of dam integrity … and are signed and stamped by a professional engineer.” Each coal impoundment report provided a hazard potential rating of less than low, low, significant, or high, which the EPA says was “not related to the stability of the impoundments but to the potential for harm should the impoundment fail, and the EPA requested operators “implement the recommendations in the reports and provide plans for taking action.”