That's 1.06 billion gallons, 100 times the Exxon Valdez spill, and this stuff is pouring into two feeder tributaries of the Tennessee river. The Tennessee, in turn, is a drinking water source for Chattanooga, west Tennessee, and the states of Kentucky & Alabama.
Clean coal, indeed.
Coal ash has high levels of mercury, arsenic and lead, and is more radioactive than spent nuclear waste (Scientific American, thanx for that happy little nugget of info), thanks to the two major radioactive impurities found in coal, uranium and thorium. When the coal is burned, anything that is NOT combustible is stored in concentrated form in the ash. Then the ash is very carefully piled up in enormous mounds inside earthen dams that are sort of affected by stuff like, well, rain, and so on. Yes, there had been warnings about this particular cell and it's ability to hold in the contents.
There are always warnings that officials decide not to act upon, and hope for the best. This is known as laissez-faire.
Now, this is not the first time this has happened. And it probably won't be the last. The question is, where is the government in regulating this stuff: how it should be contained, how much can be in one place at one time, etc.? Apparently this particular sludge pond was a record-breaker. The kind of thing where the tour guide goes on about how "this here coal ash repository is three times the size of the next smallest one, and there ain't one bigger'n this'un."
Great - a "toxic-waste Titanic."