The National Transportation Board said that it released 58 photographs and 5,000 pages of documents related the rupture of Line 6B of the Lakehead pipeline system in Marshall, Mich., as part of its investigation.
The NTSB said Enbridge Energy Partners, the pipeline operator, was notified of the leak on Line 6B on the morning of July 26, 2010.
"The pipeline had ruptured 17 hours earlier and spilled about a million gallons of crude oil into the immediate area resulting in extensive environmental damage to Talmadge Creek and the Kalamazoo River," the NTSB said in a statement.
The NTSB said the rupture on the pipeline measured about 6 feet by 4.5 inches at its widest location.
Enbridge last week issued a proposal to the Michigan Public Service Commission to replace more than 200 miles of Line 6B, part of the oil pipeline system transporting so-called tar sands oil from Canada.