Hartford Courant: The accidental release of a tsunami of coal ash and water just before Christmas across 300 acres and several waterways in eastern Tennessee is a timely reminder that, as a source of energy, coal has drawbacks. National policy must be based on a clear-eyed assessment of coal’s real, overarching costs. The sludge spill — at 1 billion gallons, probably the nation’s biggest — resulted from a breach in a holding pond at the Kingston Fossil Plant, a Tennessee Valley Authority generating …