MADISON, Wis. (AP) — The state Department of Natural Resources is investigating contaminated soil near the Bad River Band of Lake Superior Reservation in far northern Wisconsin.

DNR officials said Enbridge Inc. reported a contractor had encountered soil suspected to be contaminated along the company’s Line 5 pipeline south of Ashland about a mile west of the reservation.

Enbridge officials said they couldn’t find a leak in the pipeline and believe the contamination was from a past discharge, according to the DNR. Agency staff have visited the site several times and haven’t detected any additional petroleum odors or soil staining, department officials said.

Enbridge spokeswoman Juli Kellner said “only a trace amount of product” was found during scheduled system maintenance. She said the line was shut down as a precaution.

Line 5 runs from Superior to Sarnia, Ontario, crossing about 12 miles of the Bad River’s reservation. Enbridge is looking to reroute 41 miles of the pipeline south of the reservation after the tribe sued in 2019 to have the section crossing its lands removed.

The DNR is currently finalizing an environmental impact statement for the project. The agency’s draft environmental impact statement drew intense criticism from environmental groups, tribal members and activists who argued it didn’t adequately evaluate impacts, including the risk of spills.