The U.S. Environmental Protection Agency has been sued by two national environmental advocacy groups for allegedly failing to ensure eight Texas coal-fired power plants are meeting approved emission standards.The Austin American-Statesman reported the suit was filed last week after the EPA missed a deadline to stop the Texas Commission on Environmental Quality from exempting the coal plants from regulations limiting particulate matter emissions.An attorney with one of the groups, the Environmental Integrity Project, said the groups have been challenging the TCEQ exemptions since 2010.“Essentially, Texas has these emission limits for particulate matter,” Clark-Leach told the American-Statesman. “Particulate matter is soot,