A government probe has found negligence by the Canadian company Enbridge led to the 2010 oil spill in the Kalamazoo River — the most expensive onshore spill in U.S. history. More than 840,000 gallons of oil spilled into Michigan waterways after the rupture of an underground oil pipeline carrying Canadian oil into the United States. On Tuesday, the National Transportation Safety Board released a probe confirming Enbridge was aware as early as 2005 that its pipeline was cracked and corroded but failed to take action. NTSB chairman Deborah Hersman and board member Robert Sumwalt said Enbridge had ignored a number of red flags.

Deborah Hersman: “For more than 17 hours in over three shifts, the people controlling the pipeline did not respond to the alarms, the pressure differentials, or even follow their own safety procedures that were established following another catastrophic release in 1991.”

Robert Sumwalt: “It’s evident that this accident did not just occur because of corrosion in a pipeline. What this investigation has shown is that this accident was the result of corrosion throughout many vital safety aspects of the Enbridge organization.”

Enbridge’s safety mechanisms were so flawed that the company didn’t know its pipeline was gushing oil into the Kalamazoo River for 17 hours, during which it twice pumped more oil into the ruptured line.