InsideClimate News: Two and a half years after the costliest oil pipeline spill in U.S. history, the company responsible for the disaster is balking at digging up oil that still remains in Michigan's Kalamazoo River. The cleanup has been long and difficult because the ruptured pipeline was carrying bitumen, a heavy oil from Canada's tar sands region. Bitumen is so thick that it can't flow through pipelines until it's mixed with liquid chemicals to form diluted bitumen, or dilbit. When more than one million gallons...