The engineers find risks of an eventual spill, during the expected 50-year lifetime of the project, to be too high, "and the unrefined bitumen too toxic and hard to clean up to be acceptable for a pristine coastline."

"In fact a 200-year return period (as Enbridge identifies) means there is a 22 % probability there will be at least one spill during the 50-year operational lifetime for the project," the engineers explain.

"That's much higher than standards normally accepted in the design of civil infrastructure with high consequences in the case of failure."

"When you add in 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 incident during a 50-year operational lifetime."

The analysis concludes: "This is clearly an unacceptable risk."

For the purposes of this engineering analysis a spill is defined as greater than 5,000 cubic meters, about one seventh the size of the Valdez spill.