As such, the marine oil-spill response plan — which the company points out it has taken on voluntarily, above and beyond Canadian regulations — does not need and does not include measures to remove oil from the ocean floor, a regulatory review panel heard Wednesday.
That panel is currently examining the project's marine oil-spill plans.
"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 experts answering questions under oath this week.
Experience and lab tests show diluted bitumen weighs less than water, Maki said.
"It is an immutable fact of physics that they will float. They simply cannot sink in water."
That claim brought lawyers representing six First Nations and environmental groups to their feet to dispute the statement and demand a copy of the report cited by the company.
There is no scientific consensus on the behaviour of diluted bitumen in a real-life spill situation.
Documents obtained by The Canadian Press under access to information last summer included a request from the head of the Fisheries and Oceans' Offshore Oil, Gas and Energy Research section for further study — a request that appears to have been denied.
Chris Jones, the lawyer questioning the company experts on behalf of the B.C. government, pointed out Northern Gateway itself has committed to further research on diluted bitumen as part of its application, as well as participation on a scientific advisory committee.
"Why is all that scientific work necessary if Northern Gateway is so confident that diluted bitumen won't sink?" Jones asked.
The research and committee were recommendations of Environment Canada, consultant Owen McHugh told the panel.
"We understand that this is a contentious project and there are issues that people want explored, and we felt this was an appropriate avenue to have those issues explored, so that's why we committed to this group," he said.
ForestEthics, Raincoast Conservation Foundation, and the Living Oceans Society, along with the Haisla, Haida and Heiltsuk First Nations, have submitted to the panel that diluted bitumen does sink, making it extremely difficult — if not impossible — to clean up.
"The issue of whether bitumen will sink or float is a critical issue that is very important to these hearings," said Karen Campbell, the lawyer for the environmental groups.
The inability to clean up diluted bitumen means a spill would be catastrophic to the environment and marine species, the environmental groups argue.
Bitumen is a thick oil product similar to molasses at room temperature, according to Alberta Energy. At one time, it was used for roofing and paving.
To move bitumen through a pipeline, it must be diluted into a substance known as "dilbit."
In the case of Northern Gateway, the bitumen would be diluted with natural gas condensate. The natural gas condensate would flow from B.C. east to Alberta in one of the twin pipelines, while dibit would move in the opposite direction to a tanker port in Kitimat, B.C.
Environmental groups argue dilbit is also more corrosive than conventional crude, meaning it corrodes pipelines, increasing the likelihood of a land-based spill. Last year, the U.S. Department of Transportation's Pipeline and Hazardous Material Safety Administration asked the National Academy of Sciences to study diluted bitumen.
Northern Gateway says that is not the case. Pipelines have been carrying dilbit from Alberta for 30 years, said spokesman Paul Stanway, and the frequency of spills is no greater than conventional oil pipelines.
B.C. Environment Minister Terry Lake said the question of how dilbit behaves is "something we remain concerned about."
Lake said there are also lingering questions about details of the spill response plan — like who pays: Gateway or the federal government.
"They said they'd be willing to pay if they had to," he said. "Those are questions that remain up in the air, and I think Canada has to come forward and set clear rules and regulations so that everyone knows what their responsibilities are and we can have more detailed answers to some of these questions."