Michigan marks 3rd anniversary of oil spill ANN ARBOR, Mich., July 26 (UPI) -- There's always a chance of failure when dealing with mechanical equipment and oil pipelines, Canadian pipeline company Enbridge said. Friday marks the 3rd anniversary of the rupture of Line 6B, part of a regional pipeline network operated by pipeline company Enbridge. The rupture released about 20,000 barrels of oil into southern Michigan waters near Kalamazoo and was the costliest onshore incident of its kind in the United States. Demonstrators in Michigan protested the company as it worked on pipeline repairs ahead of the anniversary. Enbridge spokesman Jason Manshum told Michigan Public Radio there are no guarantees for oil pipelines. I would love to say that we have done the following ten items that will ensure there are no leaks again. I would love to tell you that. But I can't," he said in an interview broadcast Thursday. We're dealing with mechanical equipment and any time you deal with mechanical equipment there's a chance for some sort of failure. Henry Henderson, director of Midwest operations for the Natural Resources Defense Council, said Friday's anniversary is a "sobering reminder" of the lingering threat from tar sands. Enbridge, however, said it set a benchmark of zero incidents from its pipeline networks. The company spent nearly $1 billion on clean up costs associated with the July 26, 2010, spill.