British Columbia's new NDP government will argue its case against the expansion of the Trans Mountain oil pipeline by turning on its head the federal government's contention that the project is in the national interest.

Lawyers for the province will be in court next week seeking to overturn the federal approval of Kinder Morgan Inc.'s project.

The B.C. legal strategy is being shaped by lawyer Thomas Berger, a former judge with a deep background in resource and Indigenous issues. He has crafted a simple argument: That Ottawa failed to evaluate the project's risks to the marine environment, which is a breach of its obligation to consider the national interest.

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Ottawa approved the controversial pipeline project last November, stating that the economic benefits of getting Alberta's landlocked oil resources to tidewater are in the national interest. But Mr. Berger will argue that the federal cabinet did not give equal and independent consideration to the environmental and economic risks British Columbia and its people would bear.

"The benefits are mostly to one province, and the risk to another. Cabinet has an obligation to consider both," Mr. Berger said in an exclusive interview with The Globe and Mail.

"But in the cabinet's own reasons, they do not take those risks into account, and that is a failure to weigh fairly the considerations. … We are saying it is a matter of the public interest to all Canadians to preserve the pristine environment of British Columbia's waterways."

He played down the friction the issue has created between two neighbouring NDP governments.

"We are not seeking to pit two provinces against each other. These are matters of public policy that the federal cabinet is required to consider," Mr. Berger said.

Changing sides

In the judicial review of the cabinet decision, the Federal Court of Appeal will hear, over the span of two weeks, 14 applications to overturn the approval of the $7.4-billion project, which would triple the capacity of the Kinder Morgan pipeline that runs from Edmonton to a marine terminal in Burnaby. First Nations, municipalities and environmental organizations make up the 14 applicants.

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The province was granted intervenor status in the judicial review at the 11th hour, and has put together its case in less than seven weeks. The Globe has reviewed B.C. and Alberta's legal filings for the judicial review.

Up until a few months ago, British Columbia was on the same side as Alberta.

But that changed after the B.C. election in May. The NDP toppled the Liberal minority government after forming an alliance with the Green Party that focused, in part, on a mutual interest in killing the project.

Now, two NDP governments will square off in court over the pipeline that links their two provinces. Premier Rachel Notley of Alberta and Premier John Horgan of B.C. may be old friends, but they will be opposing intervenors with a battery of lawyers each.

The BC Liberals approved the pipeline after signing what they described as a $1-billion deal with Kinder Morgan. B.C.'s New Democrats and the Green Party promised voters that they would use every trick in the book to overturn Ottawa's approval of twinning the existing pipeline, which will dramatically increase the number of oil tankers plying the waters off B.C.'s West Coast.

Mr. Horgan, who brought with him to the Premier's Office an old jam jar filled with heavy oil to remind him of the risks of increased oil tanker traffic to the province's coastline, retained Mr. Berger to find the tools that could allow British Columbia to block the bulldozers.

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Ms. Notley has dismissed British Columbia's chances of overturning the pipeline permit: No province can "hold hostage" another's economy, she said in May, when it was apparent that the B.C. government was about to switch sides and oppose the project.

"It is our view that there are no tools available for a province to overturn or otherwise block a federal government decision to approve a project that is in the larger national interest," she said then. "If there were such tools, Canada would be less a country and more a combination of individual fiefdoms fighting with each other for advantage."

In its court filings, Alberta argues that the project fits into Canada's national climate plan and meets the strictest of environmental standards while creating 15,000 middle-class jobs.

Alberta will also point out that B.C. already approved the project – the former Liberal government negotiated the $1-billion revenue-sharing agreement with Kinder Morgan that would bring annual payments of up to $50-million per year for two decades.

The environment vs. the environment

The National Energy Board, in its submission to cabinet, concluded the risk of a major spill was a very low probability, and therefore acceptable. (Opponents of the project – including the B.C. government – will argue that the NEB did not correctly assess the risk.)

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The Trans Mountain pipeline leads to a terminal far inside Vancouver's harbour, where oil tankers are loaded with heavy oil from Alberta and then travel through 269 kilometres of coastal waters before reaching international waters.

"At every point along the way from the Westridge Marine Terminal to the 12-mile limit of Canada's territorial sea … it is British Columbians who will suffer in the event of a significant marine spill of diluted bitumen," the B.C. legal submission reads.

However, Alberta will argue that the federal cabinet correctly weighed the economic, social, cultural, environmental and policy implications of the project when it arrived at its decision.

"The decision falls well within the wide range of acceptable and defensible decisions on the facts and law and ought to be upheld," it states in its 22-page court submission, filed on Aug. 31.

Ms. Notley's legal team will argue that the federal cabinet order was "demonstrably reasonable" and that it is not for the courts to second-guess cabinet's discretion.

"It is for the [federal cabinet] to ultimately decide, balancing the broadest range of considerations, whether to approve the project in the public interest. It is not this court's function to reassess and reweigh the evidence to reach its own public interest determination."

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Alberta has tied the approval of the pipeline to its ability to meet its commitments to climate action, which in turn are a cornerstone of Canada's pledge to uphold the Paris Agreement on Climate Change.

Just as the judicial review begins in Vancouver, Canada's first ministers will gather in Ottawa to talk about the pan-Canadian climate action plan. It will be the first time Mr. Horgan takes the national stage, and his stand on the pipeline puts him at odds with both Alberta and the federal government.

He cannot count on a warm welcome.