Puget Sound Energy owns and operates a coal-fired power plant out of Billings, Montana, that the Sierra Club calls "the dirtiest coal plant in the West." The Colstrip Plant meets EPA emission standards and PSE touts its green-energy portfolio, with plans to triple its renewable energy supply by 2020. How does coal fit into that equation? And with coal plants generating 42 percent of America's electricity, how much impact would closing one plant have? We take a look with PSE's Andy Wappler and Anne Hedges of the Montana Environmental Information Center.