The National Transportation Safety Board, in its investigation into the 2010 oil spill in southern Michigan, found operators in Canada restarted Line 6B of the Lakehead system twice after the pipeline cracked.
Jason Manshum, a spokesman for Enbridge, told the Kalamazoo (Mich.) Gazette, that a series of "unfortunate events" led to the accident.
"We believe that all of the experienced personnel involved in the decision making that night were trying to do the right thing," he said.
The NTSB said pipeline operators in Canada believed reports of a line pressure drop were indicative of air pockets in the line and not a rupture. Enbridge authorities verified the leak about 17 hours after it occurred.
The Environmental Protection Agency estimated more than 23,000 barrels of heavy oil from Alberta tar sands spilled from the pipeline into the Kalamazoo River and nearby Talmadge Creek.
Enbridge in May reported to Michigan regulators that it planned to replace more than 200 miles of Line 6B.