CLAIRTON — North America’s largest coke producer has once again agreed to fix long-standing air pollution problems at its plant outside Pittsburgh.

U.S. Steel’s Clairton Coke Works has had a series of agreements with the Allegheny County Health Department dating to at least 2007, but the massive plant continues exceeding limits on air pollution. The company has paid more than $3.9 million in penalties since 2009.

A Pittsburgh newspaper reports the latest agreement allows the plant to continue operating for at least five years while it makes fixes. U.S. Steel also agreed to another $25,000 in penalties.

A Pennsylvania environmental group said in January it planned to sue over clean air violations. Penn-Future says it might seek to intervene in U.S. Steel’s latest settlement with the health department.