DULUTH – The Minnesota Pollution Control Agency is investigating a drilling fluid spill that occurred on the Willow River in Aitkin County at one of Enbridge's construction sites for its new Line 3 oil pipeline.

Drilling was halted after the nontoxic spill was discovered early July 6 and "containment and cleanup activities were started," MPCA spokeswoman Cori Rude-Young said Monday, July 12.

"The MPCA has been in regular communication with the on-site, independent environmental monitors and Enbridge Energy, and we have inspected the site cleanup," she said.

The new pipeline will replace the Enbridge's current Line 3, which is deteriorating with age and can now only carry about half of its capacity. It is more than 60% completed.

The site where the spill occurred is one of several along the 340-mile route where Enbridge is undertaking horizontal directional drilling to bury its $3 billion pipeline below waterways. The drilling method involves sending a pressurized mud mixture into a tunnel beneath a stream bed before pulling the pipe through.

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Between 80 and 100 gallons of drilling mud were released, according to the MPCA.

"There were no impacts to any aquifers nor were there downstream impacts because environmental control measures were installed at this location," Enbridge spokeswoman Juli Kellner said in a statement. "The drilling operation was immediately shut down, and crews followed the procedure for managing containment and cleanup of material as specified in project permits."

The company will need clearance from the MPCA before resuming drilling at the site, which is outside of Palisade in Aitkin County.

"The drilling mud released was bentonite clay, water and a xanthan gum additive called SandMaster approved by the MPCA's 401 water quality certification," Rude-Young said. "Xanthan gum is a nontoxic, sucrose-based emulsifier more commonly used as a food additive."

Pipeline opponents seized on the spill and said the drilling mud, though approved by regulators, "is composed of fine particles which can smother aquatic life."

"Water protectors were at Willow River to prevent the very harm that was occurring," said Aitkin County resident and pipeline opponent Shanai Matteson.

Protesters have continued locking themselves to equipment, blocking construction and facing arrest across Minnesota in recent weeks. A mass gathering is planned Thursday at the Shell River Campground.

Enbridge plans to have the pipeline, which will carry 760,000 barrels of oil per day from Canada to Superior, Wis., in operation by the end of the year. It takes a partly new route to replace the existing Line 3, which is running at half capacity due to corrosion.

In addition to the drilling mud release, the MPCA is continuing to investigate "dewatering discharges" that have allegedly "been noncompliant with MPCA authorizations," according to a letter sent in March to the Minnesota Department of Natural Resources. The DNR recently approved Enbridge's request to move 10 times as much water as originally planned throughout the project — about 5 billion gallons.

©2021 StarTribune. Distributed by Tribune Content Agency, LLC.