The Enbridge Northern Gateway proposal to ship oilsands bitumen from Kitimat along the B.C. coast carries an unacceptable risk of a significant spill, according to an independent analysis by three professional engineers.

The engineers, who include two emeritus professors from the University of B.C., find that the risks of an eventual spill are too high through the expected 50-year lifetime of the project, “and the unrefined bitumen too toxic and hard to clean up to be acceptable for a pristine coastline.”

The independent analysis generally agrees with Enbridge’s estimate that a spill of a volume greater than 5,000 cubic metres will occur, on average, every 200 years.

But the analysis notes this does not equate with a spill every 200 years (the so-called return period), only an average time between spills of 200 years.

“In fact, consistent with a 200-year return period, there is a probability of 22 per cent that there will be at least one spill during the 50-year operational lifetime for the project,” the engineers explain in a summary of the technical document supplied to The Vancouver Sun.

“That’s much higher than standards normally accepted in the design of civil infrastructure with high consequences in the case of failure (earthquake design, important bridges, etc.).

“When the analysis added the liquefied natural gas tanker traffic projects already under construction, approved or awaiting approval for the port of Kitimat (432 tankers per year), the return period of an incident (tanker collisions or groundings) decreased to 38 years, or a 73-per-cent chance of at least one such an incident during a 50-year operational lifetime.”

The analysis concludes: “This is clearly an unacceptable risk.”

The three experts who conducted the analysis are Ricardo Foschi and Robert Sexsmith, both emeritus engineering professors at UBC, and Brian Gunn, a retired professional engineer who is currently president of B.C.’s Wilderness Tourism Association.

The analysis has been formally filed with the federal Joint Review Panel investigating the $6-billion Northern Gateway proposal.

Enbridge spokesman Ivan Giesbrecht said the company would provide a formal response to the panel by Sept. 14.

Known as Dilbit, diluted bitumen is a mix of heavy crude oil and a condensate that allows it to flow through a pipe, the analysis explains. When Dilbit spills occur, the condensate separates from the bitumen and “forms a toxic cloud, poisonous to all life around the spill,” it said.

And whereas lighter oil floats on the surface of water where it is easier to clean up, “bitumen sinks to the bottom in fresh water and to a level below the surface in saline water.

“In both cases it is almost impossible to clean up and tides and currents can spread it over vast areas, with severe and catastrophic consequences for fisheries, marine life and human safety.”

In an interview Friday, Gunn said that a 5,000-cubic-metre spill is the equivalent to about one-seventh of the 1989 Exxon Valdez spill in Alaska, and about twice the size of the Enbridge spill in the Kalamazoo River in Michigan in 2010.

Gunn said he sought out the expertise of Foschi and Sexsmith to assist him in the analysis based on his concerns over the impact of an oil spill on the coast.

“It’s related to my involvement with the wilderness [association] and being up the coast and involved in land-use planning in the Great Bear Rainforest. I care about what’s happening.”

lpynn@vancouversun.com