The Environmental Protection Agency’s Office of Inspector General will audit the agency’s review of a permit for PolyMet’s proposed copper-nickel mine near Hoyt Lakes — set to be the first of its kind in Minnesota — to determine if the Clean Water Act and other regulations were followed.

Khadija Walker, the Office of Inspector General’s acting director, said in a letter Wednesday to Cathy Stepp, the EPA’s Region 5 administrator, that an audit of PolyMet’s national pollutant discharge elimination system, or NPDES, permit would take place after receiving a hotline complaint.

“The (Office of Inspector General’s) objective is to determine whether the EPA followed appropriate Clean Water Act and NPDES regulations to review the PolyMet permit approved by Minnesota and issued in 2018,” Walker wrote.

The letter was sent the same day documents detailing EPA concerns on PolyMet’s draft permit were released.

The documents show the EPA was concerned an earlier draft permit for the mine would not meet the standards set in the Clean Water Act unless the Minnesota Pollution Control Agency made substantial changes to the permit because the draft permits lacked water-quality-based effluent limitations — standards that ensure bodies of water receiving discharged water are not polluted.

The MPCA issued that water pollution permit and air permits to PolyMet later in 2018 after reviewing those comments and concerns and sending a revised draft permit back to the EPA in October 2018. The EPA made no additional comments on the revised permits before the MPCA awarded the final permit to PolyMet.

In a statement Thursday, an MPCA spokesperson maintained the process was rigorous and that the appropriate changes were made prior to granting PolyMet its permit.

Responding to criticism of the EPA’s concerns, EPA spokesperson Michael Abboud said in an emailed statement to the News Tribune Thursday evening that the agency was confident in the changes the MPCA made to the permit before it was issued.

“EPA provided the comments and recommendations our regional staff compiled on the proposed PolyMet mine in Minnesota,” Abboud said. “These comments and recommendations were discussed with the Minnesota Department of Natural Resources, PolyMet Mining Company, and other interested stakeholders. As a result the permit was changed to reflect many of EPA’s recommendations.”