Andy Knott | St. Louis Public Radio

Andy Knott

Ameren's 2,400-megawatt plant near Labadie, Missouri, is the state's largest coal-fired power plant. It produces an average of 550,000 tons of coal ash each year.
Véronique LaCapra | St. Louis Public Radio

A federal judge on Monday ordered Ameren Missouri to install devices at its power plants in Festus and Labadie to remove harmful air pollutants. 

U.S. District Judge Rodney Sippel ruled that Ameren has 90 days to apply for a Clean Air Act permit from the Missouri Department of Natural Resources to install scrubbers at the Rush Island Energy Center in Festus.