U.S. Steel has agreed to settle a lawsuit that accused the Pittsburgh-based company of violating federal clean air laws by operating plants without its desulfurization controls for more than three months, emitting clouds of sulfurous gas into surrounding towns.

The settlement with environmental groups Clean Air Council and PennEnvironment and the Allegheny County Health Department was filed in federal court Monday for a judge to review, the groups said.

PennEnvironment and the other plaintiffs accused the steel producer of more than 12,000 violations of its air pollution permits.

They put the value of the settlement at $42 million, including $37 million worth of improvements to U.S. Steel’s pollution control and plant reliability systems at its Mon Valley Works plants.