Opponents of the $7.4-billion Trans Mountain pipeline expansion are in the Federal Court of Appeal arguing that risks to endangered orcas were ignored when the project was approved.

The pipeline expansion, which will pump oil from Alberta to B.C. and offer access to global markets, is expected to potentially increase coastal tanker traffic seven-fold, according to Vancouver's mayor.

Conservation groups say that could push southern resident orcas — the estimated 76 remaining — to the brink of extinction.

Opponents have formed a consortium to fight the project, arguing First Nations and environmental concerns were ignored.

They're also raising safety fears because the pipeline would run through populated areas and are questioning whether market demands will even support the controversial venture.

"It's insane to be building this pipeline," said Karen Wristen of Living Oceans, who addressed the federal court Wednesday with concerns about the whales.

"There is just no way you can approve a project that is going to create a seven-fold increase in tanker traffic without damaging the whales. It's contrary to the Species at Risk Act."

A two-week hearing, which began Monday, now involves municipalities, environmental groups and six First Nations, all opposing the approval of the pipeline expansion.

The hearings consolidate several lawsuits originally filed by seven First Nations, Burnaby, Vancouver, the Raincoast Conservation Foundation and Living Oceans Society.

This week, the Musqueam First Nation withdrew from the case, announcing it still had "unresolved issues" with the pipeline's approval but was exploring "other opportunities."

The project proposed by Trans Mountain — a subsidiary of Kinder Morgan Canada — would triple the capacity of the pipeline, which runs from Alberta to B.C.

The federal government approved the project last year.

The company says the pipeline is crucial to future energy needs.

A request for an interview with Trans Mountain officials was declined, but the company explained in an email that the NEB, federal government and province scrutinized the project for years before approval.

"[They] assessed and weighed the various scientific and technical evidence through comprehensive review processes, while taking into consideration varying interests on the Project. The approvals granted followed many years of engagement and consultation with communities, Aboriginal groups and individuals," said Ali Hounsell, a spokesperson for the Trans Mountain Expansion project.

Pipes are seen at the pipeyard at the Trans Mountain facility in Kamloops, B.C. (Jonathan Hayward/Canadian Press)

But opponents have long claimed the National Energy Board's approval process is flawed and Indigenous groups were not properly consulted, nor was the impact on the marine environment properly considered.

Wristen and others also point to new research from the Centre for International Governance Innovation that casts doubt on whether the expansion even makes economic sense, with questions about how much demand there is for the oil from countries like China.

Tanker traffic vs. whales

Wristen said more oil flowing to the coast would cause an estimated 800 trip increase of tanker ships.

The noise that would create would harm whales, she said.

Research has shown the underwater din or "acoustic smog" from ship traffic can confuse orcas and dolphins, hampering their ability to communicate and hunt prey.

She said B.C.'s resident orcas are endangered and already stressed, due to dwindling Chinook salmon runs.

According to research funded by the Raincoast Conservation Foundation, if too many orcas are killed by boat strikes, stress from noise pollution and starvation, the population could easily dip lower than 30 animals — and that would mean extinction.

Wristen said the NEB was legally shortsighted when it evaluated the project, ignoring the Species at Risk Act.

"The NEB just tried to skirt that by saying we don't need to look out there. This project stops at the Westridge Terminal," she said.

Critics say case doomed

But court watchers and critics — like former environment minister Moe Sihota — have predicted that the opponent group has little chance of winning in court.

Prime Minister Justin Trudeau's cabinet approved both Kinder Morgan's Trans Mountain pipeline plans and Enbridge's Line 3 back in November 2016.

"They are asking the courts to substitute a court's opinion to that of cabinet. And courts have traditionally been reluctant to do that," Sihota told CBC on Tuesday.

Wristen disagrees.

"I think we have strong legal arguments or we wouldn't be in court," she said.

Today in court, lawyers for the cities of Burnaby and Vancouver also argued that alternative sites were not considered and there are too many dangers running the pipeline through some of the most populated areas of the Lower Mainland.

Eugene Kung, an environmental lawyer with West Coast Environment Law said "Canada promised a two-way dialogue, but it was evident over and over again that the discussion was only one way."