The past mishap provides some clues about what might happen. On Sunday, July 25, 2010, one of Enbridge’s pipelines in the U.S. sprung a leak near Marshall, Mich. By the time the spill was contained some three days later, some 20,000 barrels of diluted bitumen had leaked from the pipe and entered a tributary of the Kalamazoo River. At the time the river was in a flood stage, which slowed the oil’s transport downstream. Even then the oil contaminated a 65-kilometer-long stretch of river, overtopped several dams and deposited itself onto the vegetation in the flood plain. The contaminated flora had to be stripped away and taken to landfills, after detergents and water sprays wouldn’t budge the stuff. Ditto with surface soils; once spilled, the dilbit became heavier and thicker as the diluting component of the mix evaporated into the air. “When it loses the diluent it turns back to its original tarry nature and it sticks to things. It's next to impossible to get off,” Michigan State's Hamilton says.
Then there was the oil that became submerged in river sediments. “One of the big questions when we're talking about dilbit is, does it float or does it sink?” DFO’s Lee says. “If you talk to Enbridge or some of the people in industry, they say, ‘well, it floats.’ You look at what happened in the Kalamazoo river, and it sank.”
The physical and chemical properties of oil products change as they are exposed to the open environment in a process known as weathering. Typically oils float, Lee says, but evidence from the Kalamazoo spill, and results of early lab tests, suggest that as dilbit interacts with fine particles suspended in the water column, like the sediments found in river water, it sinks. "Dilbit in its initial form for a period of days to weeks is not an unusual product,” says Jeff Green, a consultant to Enbridge’s Northern Gateway and technical coordinator for its environmental assessment. “If it does take on heavy sediment loads and weathers, it can sink, and so it can become a nonfloating hydrocarbon.”
Knowing whether dilbit sinks or floats and under what environmental conditions remains a key step to planning an effective spill response. If dilbit sinks, what clean up strategies and technologies exist to recover it from the river bottom or ocean floor? In the Kalamazoo dilbit spill, Enbridge stirred up the river bottom to loosen and recover the oil. Lee points out that this approach was not effective in conditions colder than 4.4 degrees Celsius, which could pose a problem in colder northern river systems. “In my mind, this is an unproven technique,” Hamilton says. The results of EPA-commissioned experiments testing its effectiveness last summer have yet to come in.
No one knows what fraction of the 3.1 million liters of spilled dilbit in Michigan became what has since been termed “submerged oil,” but it was enough to contaminate hundreds of acres of river sediment. Three years and nearly $800 million dollars of cleanup efforts later, Enbridge and the EPA still have more work to do. As a last resort, they will likely dredge the river bottom and dispose of the contaminated sediment in landfills this summer. “We've basically had to destroy the environment to recover the submerged oil,” Hamilton says.
The ecosystem has bounced back quite well, however. Along the river, fish, aquatic insects, birds or mammals appear healthy, Hamilton reports. “You have to remember that thousands of workers stripped every visible patch of oil off the landscape. So if it were in an environment where you couldn't do that, then it wouldn't be bouncing back like it is now,” he notes. “I can't imagine what sort of environment that might be but it could be anywhere along the proposed route of the [Northern Gateway] Pipeline where you've got rugged terrain or rivers or steep gradients, or it could be in the port where it goes into deep bays. It would be next to impossible to clean up.”