The final verdict is in: diluted bitumen sinks in seawater. According to a November federal government report released Tuesday. Bitumen is a heavy oil mined in the Alberta oilsands. Due to its high viscosity, bitumen is mixed with a cocktail of light thinning chemical diluents to increase its flow in pipelines.

The results of the study, which recorded the behaviour of diluted bitumen in turbulent and sediment-laden sea water, settle a significant debate regarding the prospective risks posed by the Northern Gateway pipeline and oil tanker traffic to the ocean ecology off the B.C. coast.

The report also confirmed the use of toxic chemical dispersant Corexit 9500, made infamous after its widespread application in the Gulf of Mexico following the BP Deepwater Horizon well blow out, is limited in its ability to disperse diluted bitumen.

The study looked at two bitumen blends, Access Western Blend and Cold Lake Blend, which contain the highest volume of bitumen in products transported via Canadian pipelines between 2012 and 2013.

The study fulfills one of the 209 conditions placed on the approval of the Northern Gateway Pipeline by the National Energy Board’s Joint Review Panel.

In December the panel recommended the federal government approve the pipeline which will carry 525,000 barrels of oil to the B.C. coast daily.

In November 2013 expert witnesses for Enbridge’s Northern Gateway pipeline argued diluted bitumen would not sink in the event of a marine spill.

“I don’t know if it’s possible to drive a stake through the heart of this concept of sinking oil, but every one of these liquids that we’re talking about is no different from any other liquid we have on Earth,” said Al Maki, one of 10 Northern Gateway experts answering questions before the panel.

Maki claimed both experience and laboratory test confirmed diluted bitumen weighs less than water.

“It is an immutable fact of physics that they will float. They simply cannot sink in water.”

Karen Campbell, staff lawyer for Ecojustice and representative of several environmental groups during the hearings, said the behaviour of diluted bitumen in ocean water had become the “critical issue” for opponents of the pipeline.

In late 2012 Enbridge conducted a study to measure the density of weathered diluted bitumen under simulated open-water conditions. The results of the study, Enbridge claimed, suggested bitumen would not become more dense than water and sink although the presence of sediment in the water could affect the density of the oil. “At no time during the two-week-long tests, did diluted bitumen weather to a density greater than water.”

Critics were quick to point to the limits of the laboratory study, conducted by SL Ross, which contradicted the behaviour of diluted bitumen in real-world scenarios such as the 2010 spill of the substance into the Kalamazoo River.

Triggering the most expensive on-shore oil spill in U.S. history, a ruptured Enbridge pipeline sent three million litres of diluted bitumen into the river. The EPA found the lighter chemicals evaporated from the bitumen, leaving the heavier crude to mix with sediment and sink to the riverbed.

“Some have suggested that diluted bitumen weathers rapidly, with diluent evaporating leaving bitumen behind to sink. This isn’t true,” Enbridge claims on the Northern Gateway legacy site.

The SL Ross study involved placing diluted bitumen in a tank of water and simulating weather conditions through the use of UV lights and fans. After 11 days, the majority of the bitumen remained at the top of the tank, with about 5 per cent suspended. Scientists pointed out the fact that that no sediment was present in the tank and that other conditions of the study limited its real-world implications.

At the time of the study’s release, former Environment Canada scientists Merv Fingas said emergency responders relied on oil to float in the event of a spill.  

“In Canada, emergency responders are not as prepared for submerged oil as they should be.”

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