State regulators said Wednesday they have penalized an iron ore operation in northern Minnesota for fouling wetlands.

ArcelorMittal, which operates an iron ore mining and processing facility in Virginia, sends mining waste through a pipeline to a storage basin to keep pollutants out of the environment.

But the Minnesota Pollution Control Agency said that system failed three times sometime between May 2013 and April 2014. Mining waste mixed with water and road debris made its way into 15.3 acres of wetlands, roughly the size of 11 football fields.

MPCA officials said the company hadn't inspected and maintained the pipeline and tailings basin properly and was slow to report the spills. ArcelorMittal has paid a $58,000 state penalty and was also fined $272,000 dollars by the U.S. Environmental Protection Agency.

Cleanup continues at the site, but state officials said in a news release that it isn't clear yet if the wetlands can be restored.

Environmental groups cite such incidents as reason to require in-depth studies for new or expanded mining projects. For example, some groups have asked a state court to require an environmental impact statement for Northshore Mining's proposed expansion near Babbitt. Environmental groups are also scrutinizing the tailings basin and waste plans for the proposed PolyMet copper-nickel mine.