The Sierra Club and the Montana Environmental Information Center said on Wednesday that they plan to sue the owners of the Colstrip Steam Electric Station in Montana under the Clean Air Act. The groups allege the plant has not been updated with the required pollution control equipment.


The coal-fired plant is operated by PPL (formerly known as Pennsylvania Power and Light) and owned by Puget Sound Energy, Avista Corp., PacifiCorp, PPL Montana, NorthWestern Energy and Portland General Electric. The plant, the second largest coal-fired facility west of the Mississippi, burns more than 10 million tons of fuel per year and generates 2,200 megawatts of electricity, which is transmitted to customers in Montana, Oregon and Washington.


According to the Sierra Club, the Colstrip plant is "the dirtiest coal-burning power plant in the Western states and the eighth dirtiest nationwide." The organization says pollution from the plant threatens water supplies and causes "life-threatening diseases" and points out that the county where the plant is located has the third-highest rate of asthma in Montana. A 2010 article in Sierra magazine says the coal mined in that region of Montana is of very low quality, producing only two-thirds the amount of energy as coal mined in the Appalachian region and contains a higher level of contaminants. The article says Colstrip's coal ash ponds have leached boron into local wells at levels 13 times the legal limit.


David Hoffman, director of external affairs for PPL, told the Great Falls Tribune that the company has invested more than $100 million in pollution-control technologies over the past decade, making it what he calls "one of the cleanest plants in the country from an emissions standpoint."


Parts of the Colstrip plant have been online since 1975, with the rest starting operation in 1984 and 1986. Under the Clean Air Act, power plants of this age are grandfathered out of some tougher pollution control standards unless they are modernized. Hoffman told the Associated Press than the changes were regular maintenance and do not count as upgrades.


The Environmental Protection Agency sent PPL a letter in May ordering the company to provide additional information on the scope of its upgrades to see if it is now in violation of the Clean Air Act.


The Colstrip plant directly employs almost 400 people. According to a 2010 report from the owners of the plant, more than 3,700 jobs are made possible by the plant's existence. But according to the book "Colstrip, Montana," by photographer David T. Hanson, the town would never have been settled if not for the coal that is mined around it.


The Sierra Club and Montana Environmental Information Center plan to officially file a lawsuit in 60 days. 


Related environmental story: EPA releases map of top greenhouse gas emitters in U.S.


Environmental groups announce plan to sue over emissions at Colstrip plant in Montana
The second-oldest coal plant in the Western half of the country burns more than 10 million tons of fuel per year.