MADISON, Wis. -- The state Department of Natural Resources said that an aging coal-fired power plant operated by the University of Wisconsin-Madison has violated the Clean Air Act by upgrading its boilers without installing new pollution controls.

The news comes just days after the DNR warned the same plant was violating the Clean Water Act by allowing coal runoff to seep into storm sewers that drain into Lake Monona.

The DNR said in a letter dated on Wednesday that the plant committed at least three violations by failing to obtain construction permits and install pollution-reducing technology during renovation projects between 1998 and 2004.

The letter warns the university could face fines of up to $25,000 per day if the violations are not corrected.

The Sierra Club has already made similar allegations of Clean Air Act violations in a federal lawsuit as part of its strategy to pressure the state into closing the plant.

The state Building Commission ordered a study last week into whether the 50-year-old plant should be replaced.