It's been four years since the Enbridge pipeline Line 6B broke, creating the largest inland oil spill in U.S. history.
More than a million gallons of tar sands oil have been cleaned up from Talmadge Creek and the Kalamazoo River. This summer, crews are dredging areas of Morrow Lake.
Steve Hamilton is a professor of ecosystem ecology at the Kellogg Biological Station at Michigan State University. He’s served as an independent scientific advisor to the Environmental Protection Agency throughout the cleanup. I talked with him for today's Environment Report.
A few years ago, right in the heart of the cleanup, an EPA official said the agency was "writing the book" on how to remove tar sands oil from the bottom of a river.
Hamilton agrees: "First, before it even got to the bottom, we learned that in the first year, it stuck to surfaces of plants and debris that made a tarry mess that largely had to be manually removed."
He says it was the removal of the submerged oil that made the cleanup last as long as it has.
"It is so incredibly difficult to remove submerged oil from a complex river, extending over nearly 40 miles."
But what are the lasting impacts?
Hamilton says that's a tough question. He says the river and the floodplain are a resilient ecosystem.
"It has adapted to disturbance by flooding and has been disturbed by human activity in the past. The vegetation is almost already coming back to normal. Whether there will be some residual toxic effects from the oil because we can't get it all out in the soils and in the sediments, we don't know the answer to that. It needs more study."
He says there will probably be some oil turning up for years to come.
"I wouldn't rule out the possibility of somebody stumbling across a concentrated hot spot somewhere on the floodplain that was overlooked because the oil settled down as sort of like tar patties," says Hamilton.
The oil that's left behind
Hamilton can't say for sure what the lasting effects of leaving some oil in the environment might be.
"If you look at the scientific literature, you can find plenty of evidence for long-lasting effects," he says. "One that has been studied a lot is the Exxon Valdez spill up in the Alaska marine area."
In that case, some toxic effects have been discovered from the oil persisting on beaches and in sediments. But Hamilton says the 1989 Exxon Valdez spill was a different kind of oil in a colder, marine area, and he's not sure what we might see play out in the Kalamazoo River region.
Enbridge says they are in the final stages of cleanup of the Kalamazoo River and we might see the heavier work being wrapped up soon.
"There could always be some kind of polishing going on as more sheen and more oil is discovered in the future but I think the heavy duty cleanup will be over this summer, by all indications. I hope it will," says Hamilton.