Minnesota regulators have fined Hibbing Public Utilities for exceeding its air permit's emission requirements for nearly four years.

In a news release Friday, the Minnesota Pollution Control Agency said the coal- and wood-fired steam plant in Hibbing had exceed the requirements from 2017 to 2020, resulting in a $26,947 fine.

"The violations stemmed from the boilers operating below the limits they were designed for. This causes inefficient combustion which results in excess pollution, which has been an ongoing problem with the coal-burning boilers," the MPCA said in the release. "The agreement requires the facility to submit monthly reports to the MPCA on deviations from permitted emissions and to take steps to use more natural gas in the facility and reduce its dependence on coal."

Luke Peterson, the general manager of Hibbing Public Utilities, did not respond to the News Tribune's request for comment Friday morning.

The cogenerating plant, owned by the Hibbing Public Utilities Commission, provides steam heat for downtown Hibbing buildings. and electricity for its service area.