Bloomberg: U.S. power companies may face billions of dollars a year in new costs after last week’s coal- sludge spill in east Tennessee if the accident results in regulating their wastes as toxic. The accident that unleashed a billion-gallon outpouring from a Tennessee Valley Authority power plant on Dec. 22 may revive efforts in Washington to tighten rules on so-called fly ash that’s laden with heavy metals, and other waste from coal- fired generators. The proposals stalled during the eight …