MINNEAPOLIS — A leaked email shows that a senior official sought to keep the public from knowing federal Environmental Protection Agency staffers’ concerns about the pollution risks of a planned PolyMet copper-nickel mine in northeastern Minnesota, critics of the project contend.

In a March 2018 email that Shannon Lotthammer, who was then assistant commissioner of the Minnesota Pollution Control Agency, sent to EPA regional Chief of Staff Kurt Thiedel, she asked that EPA staffers not file written comments during the state’s public comment period on the mine’s water quality permit. This kept EPA staffers’ concerns about the proposed project out of the public record, the Star Tribune reported Wednesday.

“We have asked that EPA Region 5 not send a written comment letter during the public comment period and instead follow the steps outlined in the MOA, and wait until we have reviewed and responded to public comments and made associated changes,” Lotthammer wrote in the email, which was released Tuesday by the union that represents employees of the EPA’s Chicago office, which oversees Minnesota’s enforcement of federal pollution laws. The term “MOA” refers to a memorandum of agreement the agencies signed decades ago delegating federal enforcement authority to the state.

The state approved the water quality permit in December.

Lotthammer, who is now an assistant commissioner at the state Department of Natural Resources, declined to comment about the email when contacted by the newspaper. But MPCA spokesman Darin Broton downplayed its significance, saying the two agencies spoke frequently about PolyMet’s water permit, and that the MPCA “made substantive changes” to the permit based on those conversations. He called the process “rigorous” and “professional.”

Documents that the EPA tried to keep confidential before releasing them last week show that its staffers criticized how the MPCA drafted the permit and concluded that the permit would violate federal law because it lacked pollution limits based on the state’s water quality standards. Instead of filing the documents into the public comment record, EPA staffers read the comments to MPCA staffers over the telephone.

The EPA’s inspector general’s office said last week that in response to a hotline complaint, it had opened an investigation into whether EPA officials properly followed the appropriate regulations during the permit review process. It asked Region 5 Administrator Cathy Stepp for documents from all staff and management related to the permit, including the written comments for the permit.

U.S. Rep. Betty McCollum, who has been critical of the EPA for failing to submit formal written comments and who chairs a subcommittee with jurisdiction over the EPA, faulted both agencies for a lack of transparency.