The report is expected to be released this fall, about six months later than expected, the Kalamazoo Gazette reported. The National Transportation Safety Board attributed the delay to other investigations into separate pipeline incidents.
"Our investigations look at numerous aspects that could have played a role in the accident, such as maintenance, human factors, pipeline operations, and materials," said NTSB spokesman Peter Knudson.
"We'll also look at the emergency response and environmental remediation efforts to assess how they were handled."
The report about the July 2010 spill from Calgary, Alberta-based Enbridge Inc.'s pipeline also is expected to offer future safety recommendations for the pipeline industry.
Enbridge said it will be able to finish its internal investigation after the report is released. Company spokesman Jason Manshum said the company is working to take what it's learned from the spill and share that knowledge.
"We're focused on applying these lessons in our operations in all locations where we operate," Manshum said.
Cleanup efforts continue this year. The rupture was to a 30-inch pipeline carrying oil from Griffith, Ind., to Sarnia, Ontario. The oil spilled into the Kalamazoo River and Talmadge Creek near Marshall, about 60 east of Grand Rapids.
Preliminary testing of the ruptured pipe found surface cracks and indications of corrosion. The Enbridge pipeline was installed in the 1960s and is part of a system that was eyed by federal officials prior to the leak.
The Pipeline and Hazardous Materials Safety Administration has said that it warned Enbridge about potential problems including possible safety code violations related to monitoring pipeline corrosion.