The aftermath of burning a mountain of coal isn't pretty. It's not just the ash itself; it's also the toxic elements that have been purified by fire out of the "fossilized sunshine."

Those toxic elements come along for the ride when the coal ash spills, like it did near Kingston, Tenn., on December 22, 2008. The "Christmas coal ash spill" was the largest such disaster in U.S. history and covered more than a square kilometer of land before the roughly 4 billion liters of slurry ended up in the Emory and Clinch rivers. Those stretches of river effectively died.

The rivers are now recovering, thanks to the Tennessee Valley Authority (TVA)—a government-owned corporation that runs power plants throughout that region—which may ultimately spend more than a billion dollars to clean up its coal ash mess. Even so, a scientific survey found arsenic and other contaminants at high levels in water in the rivers sediment 18 months later.

It would seem obvious, given the scale of the clean up and its impacts, that such coal ash would be considered hazardous waste.

It is not. Instead, it is put to "beneficial use" in products such as roadbeds, cement and wallboard. It's even added to soil. And when it's not being used, some companies simply dump it back into the mines from whence it first came.

Unfortunately, the toxic metals in the ash have a tendency to interact with groundwater and percolate into drinking supplies. The only way to prevent that is to dispose of the ash in specially lined landfills to prevent such leaching—something that would be required if coal ash were deemed hazardous waste.

The U.S. Environmental Protection Agency has been mulling over whether to reclassify coal ash as hazardous waste even though its analysis of the constituents of coal ash leaves no question. But the U.S. produces more than 100 million metric tons of the stuff every year and those charged with disposing of this massive amount of waste are not disposed to face additional hurdles to finding a place to get rid of it.

And that means that coal ash continues to pile up in more than 580 sites across the country, including elsewhere in the Tennessee Valley. After all, the TVA alone generates more than 6 million metric tons of such ash every year. In fact, just one month after the Christmas coal ash spill near Kingston, the TVA spilled some 37,000 liters of coal ash slurry in Alabama near Scottsboro.

So the only question is: where will the next spill be?

Editor's Note: David Biello is the host of a forthcoming series on PBS, titled Beyond the Light Switch. The series, produced by Detroit Public Television, will explore how transformation is coming to how we use and produce electricity, impacting the environment, national security and the economy.