The chairwoman of the National Transportation Safety Board this morning said Enbridge detected the defect that led to a massive oil spill in Michigan five years before it occurred, but failed to do anything about it.

Opening a hearing on the pipeline spill near Marshall in July 2010, NTSB Chairwoman Deborah A.P. Hersman said an investigation into the rupture of the 30-inch pipeline revealed several concerns, including a lack of regulatory oversight and a delay on the part of Enbridge to respond to the spill led to "significant" environmental damage.

"Pipeline operators are required to have an integrity management program, which continually assesses and addresses the safety risk on their pipelines, particularly those in high-consequence areas," Hersman said. "In 2005, Enbridge detected the very defect that led to this failure ... Yet for five years, they did nothing to address the corrosion or cracking at the rupture site – and the problem festered."