Tenn. Sludge Spill Challenges 'Clean Coal' Future

Dec. 25, 2008 -- When an earthen wall holding back 525 million gallons of ash slurry gave way at the coal-fired Kingston Fossil Plant in Tennessee in the wee hours of Monday morning, the resultant flood ruined a picturesque rural landscape, inundated more than a dozen houses, and blanketed as much as 400 acres of land with potentially toxic muck.

Fortunately, no one was hurt. And initial tests by officials at the Tennessee Valley Authority suggest the Clinch and Tennessee Rivers, major sources of drinking water for the denizens of Knoxville, Tenn., escaped major contamination.

But the mud has done much more than just sully a countryside. Americans' energy consumption habits are a top-tier political issue, and as we look for new ways to curtail global warming, wean ourselves from oil, and find sources of clean energy, coal's role is still unclear.

So the accident raises a serious question: Is there such a thing as "clean coal"?

America's thirst for energy generates leaves between 122 and 129 million tons of waste from spent coal each year. Most of that is fly ash, a fine, talcum-like powder. Bottom ash, boiler slag, and sulfur-rich solids left over from scrubbers in the plants' smoke stacks all have to be disposed of, too.

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About a third of it is recycled. Ash is very good for neutralizing acidic mine tailings, making concrete, and even enriching soils for agriculture when cleaned of its heavy metal content. Sulfur compounds left over from the scrubbers are also great for making synthetic gypsum, a prime ingredient in wallboard and highway construction.

In fact, the United States Environmental Protection Agency (EPA) sees so much value in recycling "coal utilization byproducts" that they have a plan in place to reuse 50 percent of the waste by 2011.

Holding ponds for unused ash, like the 40-acre structure at Kingston that failed this week, are still common, though, as is heaping ash into landfills.

That should be safe for the environment, said Thomas Feeley, Deputy Director of the Department of Energy's National Energy Technology Laboratory Office of Coal and Power Systems.

"In our studies, which focus on mercury, we find that metals are stable in ash materials, even when they are exposed to rain and snow," he said. Even now, bulldozers are rushing to contain and scoop up the spill at Kingston, so there's a good chance that further environmental damage can be avoided.

The EPA agrees. The agency does not consider coal ash a hazardous waste, despite the fact that it contains mercury, selenium, and arsenic, among other heavy metals.