An estimated 500 million gallons of coal-ash sludge are seeping along the I-40 Knoxville-Nashville corridor in eastern Tennessee, after an earthen wall gave way on Dec. 22 at the TVA Harriman coal-fired plant. While no casualties were reported, the coal-ash spill — the refuse left over after the plant burns the coal — should be a terrifying toxic wake-up call about the thousands of coal-fired plants and refuse-pile accidents waiting to happen across the county.

According to numerous studies, coal ash contains mercury, lead, and arsenic. And nearly 800 Olympic-size swimming pools of that toxic mix is flowing into the waterways of Tennessee now. As the Knoxville News Sentinel reported Tuesday:

Viewed from above, the scene looked like the aftermath of a tsunami, with swirls of dirtied water stretching for hundreds of acres on the land, and muddied water in the Emory River.

The Emory leads to the Clinch, which flows into the Tennessee. Workers sampled river water Monday, with results expected back today, but didn’t sample the dunelike drifts of muddy ash."

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For the millions of people downstream in Tennessee, Alabama, and Kentucky, a spill estimated to be several times bigger than the Exxon Valdez disaster in Alaska is creeping into their waterways and aquifers.

Footage of the spill can be seen here and below the fold.

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But here’s the nightmare coda: Coal ash is more toxic and radioactive than nuclear waste. According to recent studies:

… the waste produced by coal plants is actually more radioactive than that generated by their nuclear counterparts. In fact, fly ash — a by-product from burning coal for power — contains up to 100 times more radiation than nuclear waste.

According to some surveys, people living near coal-ash dumps have 900 times the national cancer rates.

Let’s hope not only that the TVA, EPA, and appropriate government agencies deal with this spill in a swift and wise manner, but also that the new Obama administration recognizes the dangers of dirty coal and accelerates its clean energy program.