A five-member panel of the National Transportation Safety Board will hear the investigators' conclusions at a meeting Tuesday, then decide whether to accept, reject or modify them before issuing a final report that will include recommendations on how to improve pipeline safety.
Oil began leaking from the line July 25, 2010, into Talmadge Creek near Marshall, about 60 miles east of Grand Rapids. It spread across roughly 35 miles of the Kalamazoo River, fouling wildlife habitat and closing a large swath of the river to boaters and anglers.
Enbridge Inc., the Canadian company that owns the pipeline, continues to clean up the oil under the supervision of the Environmental Protection Agency and has estimated its costs at more than $700 million.
Nearly all the river has been reopened, including a 34-mile section last month. Just a quarter-mile stretch of the delta between the river and Morrow Lake remains closed.
"It's a much different picture than it was a year ago and certainly than it was two years ago," Ralph Dollhopf, co-ordinator of the EPA team overseeing the cleanup, said Monday.
The U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration last week proposed a record $3.7 million civil penalty against Enbridge for what it described as 24 regulatory violations, including failure to fix corrosion problems in the damaged pipeline discovered as far back as 2004.
The agency said crews in Enbridge's control centre in Edmonton, Alberta, waited 17 hours after receiving initial alarms from its Marshall pumping station before closing valves to isolate the damaged section of pipe.
Enbridge is seeking approval from Michigan officials to replace and enlarge the entire line, which runs from Griffith, Ind., to Sarnia, Ontario.
Flesher reported from Traverse City, Mich.