The Minnesota Pollution Control Agency (MPCA) now says there have been more releases of drilling fluid along the Line 3 oil pipeline project than previously reported.
Between June 8 and Aug. 5, there were 28 releases at 12 river crossing locations, the agency said. In one of those cases, on July 6, about 80 gallons of fluid entered the Willow River in Aitkin County.
The MPCA says there were 13 spills into wetlands and 14 accidental releases in upland areas, although one of those flowed into a wetland.
The agency disclosed details about the releases on Monday in a letter to DFL state lawmakers, who had requested the information.
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Drilling fluid is used as a lubricant during the drilling process. It's made of mostly bentonite clay and is not considered toxic, but can impact aquatic life.
The MPCA said the state water permit issued to Enbridge for the Line 3 construction does not authorize the release of drilling fluid to a wetland or river. It says the releases are under investigation as potential violations.
Enbridge has said that the drilling mud was quickly contained and cleaned up under the supervision of trained environmental inspectors and independent monitors.
The Line 3 project is about 80 percent complete, and is expected to be finished by the fourth quarter of this year.