The story of coal ash keeps going nowhere. Unfortunately, the same can’t be said about coal ash.

Coal is the dirtiest fossil fuel we’ve got. BTU to BTU, we get more pollution from coal than from petroleum and way more than from natural gas. Most of the pollution goes up in smoke, so to speak. It’s emitted as gas (carbon dioxide, mercury, sulfur dioxide and nitrogen oxides) or as fine particles that find their way up through the smokestack and into the atmosphere. (See related story: “Largest U.S. Coal Ash Pond to Close, But Future Rules Still Undecided.”)

But coal has another form of waste — it’s the stuff that’s left behind after the coal has been burned. This