Environmental groups have filed a legal complaint against Midwest Generation, claiming the utility's coal ash ponds are leaching pollution into groundwater.

The Environmental Integrity Project and the Environmental Law & Policy Center filed the complaint Wednesday with the Illinois Pollution Control Board on behalf of several environmental groups.

It claims coal ash ponds at Midwest Generation power plants in Pekin, Waukegan, Romeoville and Joliet are leaching toxic pollutants such as arsenic, selenium and boron into groundwater in violation of state pollution laws. It's asking the board to order the company to stop open dumping of coal ash and to clean up contaminated groundwater.

Midwest Generation says the complaint doesn't appear to raise new issues and the company will defend itself against groups trying any avenue to shut down coal-fired plants.