The National Transportation Safety Board this week said Canadian pipeline company Enbridge knew of a defect on Line 6B of the Lakehead oil pipeline system five years before it burst open and spilled around 20,000 barrels of oil into southern Michigan waters.
Anthony Swift, an attorney and energy analyst at the Natural Resources Defense Council, said the NTSB findings suggest more transparency is needed so responders are better able to deal with future spills.
"The government investigation raises serious questions about whether corrosive tar sands can be safely moved, especially when they cross farms and waters in the U.S. heartland as the proposed Keystone XL tar sands pipeline would do," he said in a statement.
Canadian pipeline company TransCanada aims to build Keystone XL to carry oil from Canada to refineries along the southern U.S. coast.
Stephen Wuori, president of pipeline operations at Enbridge, said safety is the top priority for his company.
"Our intent from the beginning of this incident has been to learn from it so we can prevent it from happening again, and to also share what we have learned with other pipeline operators," he said in a statement.