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By itself, the pipeline that Enbridge proposes to build across British Columbia might not pose a great threat to caribou.

The problem is, the Enbridge Northern Gateway project cannot be taken in isolation. Its impact has to be assessed cumulatively with the highways, gas and power lines that already exist – and therein lies an enormous environmental challenge that could bring the project to a halt.

Chris Tollefson, a lawyer representing BC Nature and Nature Canada at the federal review hearings, seemed to recognize that last week, when he hammered away at the numbers behind Enbridge's "density threshold," which sets out how much development can take place in caribou habitat before the animals fall into population decline.

And in the process of finding out where the numbers came from, Mr. Tollefson revealed just how shaky Enbridge's caribou plan really is.

An exhibit filed with the review panel by Enbridge in May, 2010, sets out that, for assessing cumulative impact of the pipeline, the company had adopted "a corridor density of 1.8km/km2 for caribou." The figures refer to 1.8 kilometres of development within a square kilometre of habitat.

Enbridge sourced its numbers to "Francis et al, (2002)" – an apparent reference to a science paper. But Mr. Tollefson hadn't been able to find any such paper.

Caribou are threatened in B.C. because their habitat has been fractured into increasingly smaller pieces by developments.

While one road or pipeline might not do a lot of damage, enough of them stacked up together can cause caribou populations to crash. A big reason for this is that as the landscape is opened up, moose and deer proliferate, wolves move in – and caribou become prime prey.

So Mr. Tollefson honed in on the formula that Enbridge used to base its density threshold planning for caribou.

"Is it the proponent's position today that the 1.8-kilometre-per-square-kilometre threshold is conservative and based upon reliable science?" he asked.

"I think the direct answer is no, that's not the most conservative threshold, there's other thresholds," replied Jeffrey Green of Stantec Consulting, a firm hired by Enbridge to help with environmental planning.

But was it reliable science? Mr. Tollefson persisted.

That brought Colleen Bryden, another member of the Enbridge environmental team, into the mix.

"So I'll speak to the origin of the … threshold we used in the assessment … we addressed this in an errata," she said.

And indeed, Enbridge had done just that.

Turns out the reason Mr. Tollefson hadn't been able to locate the science paper was because there isn't one. The Francis et al, (2002) reference used by Enbridge is for a PowerPoint presentation made by Shawn Francis, an independent ecologist, who wasn't consulting for Enbridge, but had been speaking at a wildlife conference about Yukon caribou.

On Oct. 30 – after two years of insisting their science was sound – Enbridge quietly filed an "errata" with the panel, noting that the "threshold recommended by Francis et al., (2002) should read threshold recommended by Salmo and Diversified (2003)."

That seemed like a simple enough correction. The wrong paper had been cited. Now they had the right one. But Mr. Tollefson established in his continued line of questioning that Salmo's paper referred back to the Francis PowerPoint. So the root source was still the same.

"Is it usual for a proponent to rely upon a single source to derive a key threshold such as this, especially where that source is a non-published, non-peer-reviewed work?" Mr. Tollefson asked.

"My answer is that, when we do these assessments, we try to find the best thresholds we can," Mr. Green replied.

The problem is, the best seems to have been based on a slide show about Yukon caribou – not on peer-reviewed science about the herds in B.C., which are in decline, are listed as threatened and may already have hit their density threshold.

Enbridge's unfortunate "errata" could turn out to be a costly error, because it casts doubt on the company's plans. And in B.C., where Premier Christy Clark has been saying the pipeline offers too many risks and not enough benefits, that just might be enough to sink the project.

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