There's no way to completely eliminate the risk of spills from oil pipelines, Enbridge Inc. experts agree. (Al Grillo/Associated Press)

There will always be some risk that an earthquake or another hazard along the proposed Northern Gateway route could rupture the pipeline, the company's experts have conceded under questioning from the Haisla Nation at hearings weighing the future of the project.

Enbridge Inc. chief geotechnical engineer Drummond Cavers told the hearing Friday that risk can never be reduced to zero, but mitigating the possibility of a resulting spill is the whole focus of the design of the pipeline.

"That's why we get the seismic values, that's why we look at the geohazards and consider the geohazards along the pipeline," Cavers said under questioning from First Nation's lawyer Jesse McCormick.

"That's exactly what we're designing for, and mitigating."

McCormick then asked if there was zero chance an earthquake of a magnitude less than 7.5 would result in catastrophic failure of the pipeline.

"No, we've stated before, I think quite clearly, that we can never get the probability of a hazard down to zero," Cavers said.

McCormick later asked another Enbridge technical expert about the amount of oil that could be spilled between the time of a rupture and the time the company could detect the break and close valves to stop the flow.

"Well, release volume is determined on the basis of the topographic profile of the pipeline, and ultimately on the locations of the remotely operable valve, the isolation points," Ray Doering, manager of engineering for the Northern Gateway project, responded.

It depends on the flow rate of the pipeline, the time it takes to close 132 valves along the line, he added.

Concerns about data

The implicit uncertainty about the potential severity of ruptures and spills concerns Allan Donovan, a lawyer for the Haisla First Nation.

Crews in Marshall Township, Mich., clean up oil from the Enbridge pipeline leak in July 2010. (Paul Sancya/Associated Press)

Donovan said he’s worried the Joint Review Panel won’t have enough data to make an informed decision on whether or not the pipeline should proceed.

"It's certainly a big open question at this stage, if the evidence is there, or whether we just have to step back from the process, everyone do a bit more homework," Donovan said.

But Enbridge vice-president Janet Holder points out the company has already done a lot of homework, submitting more than 20,000 pages of evidence to the panel.

Holder said more detailed answers will come if and when the pipeline is approved, and that approval would no doubt come with conditions.

"And we have to live up to those conditions. I think people were thinking we're already at the stage that if they handed us a certificate we could go ahead and build, and that's not where we're at."

One of the proposed $6-billion twin pipelines would carry diluted bitumen from the Alberta oilsands about 1,100 km to a tanker port planned for Kitimat, B.C. The other pipeline would carry condensate from natural gas from Kitimat back to Alberta.

The company says the project will boost Canada's GDP by $270 billion over 30 years, and would generate total revenues in direct and indirect benefits to the federal and provincial governments of $81 billion over 30 years. Of that, B.C. would receive about $6 billion, while Ottawa would receive about $36 billion and Alberta $32 billion.

The pipeline would traverse 1,100 km of northern B.C. and Alberta. (CBC)

But dozens of First Nations, conservation groups and individuals fear irreparable harm will result from a catastrophic oil spill, either from the pipeline on land as it traverses the pristine wilderness of northern B.C., or at sea, from hundreds of tankers that will navigate Douglas Channel to deliver the oil to the shores of China.

The Joint Review Panel hearings continue Saturday.

Next week the focus of the hearings shift to emergency response and preparedness.

With files from the CBC's Marissa Harvey