MADISON, Wis. -- State officials are saying that it will take further study to determine whether 26 maintenance projects at state-run power plants violated federal clean air rules.

State employees plan to review whether the projects at 13 coal-fired power plants complied with the U.S. Clean Air Act. The law requires plants to install modern pollution controls when they undergo major renovations.

The state Department of Administration was required to release a list of potentially problematic maintenance projects at the plants by Friday under a settlement with the Sierra Club.

The environmental group sued the state over Clean Air Act violations at a University of Wisconsin-Madison power plant. The suit uncovered potential problems elsewhere around the state.

Administration spokeswoman Linda Barth said the state will make sure that all the plants are brought into compliance. That could require the plants to implement pollution controls, use different energy sources or be replaced in coming years.