Why this Canada-U.S. pipeline has emerged as a midterm election issue in the U.S. Midwest

OTTAWA — A frightening scene played out on Tuesday morning, when a parked semi-truck rolled into an excavation site and hit an exposed section of the Enbridge Line 5 pipeline near the Wisconsin-Michigan border.

Drone footage that was widely circulated online showed a thick, white cloud of natural gas spreading from the accident site to a meadow on the other side of a dirt road.

While the leak was quickly isolated and no injuries were reported, the incident exacerbated an already tense political divide around the Canada-U.S. pipeline.

Fred Clark, a Democrat running for Congress in northern Wisconsin, quickly called on the state’s department of natural resources to halt work on Line 5 until a “thorough review of Enbridge’s construction methods and safety protocols can be conducted.”

“ Based on these incidents it’s clear that Enbridge does not have all of the details right when it comes to ensuring that this project can be executed safely,” said Clark in a press release.

The department sent Enbridge a letter on Thursday asking the Calgary-based company to stop work in the area while it investigated the spill. The letter didn’t say how long the investigation would take.

Tony Evers, Wisconsin’s Democratic governor, said he was “exceedingly concerned” about the spill and “other recent events involving Enbridge,” and called on the company to work “expeditiously” with state investigators.

Michigan Governor Gretchen Whitmer, also a Democrat, filed a legal brief on Friday calling for an underwater section of the pipeline running through her state to be removed.

The timing of the spill, coinciding with competitive, high-profile statewide races in both Michigan and Wisconsin, is likely to keep Line 5 in the spotlight heading into November’s midterm elections.

Here’s what you need to know about the debate over Line 5 south of the border.

Enbridge Line 5 is a 1,038 km pipeline that runs from northern Wisconsin to Sarnia, Ont., and forms one segment of the company’s larger continental pipeline system. It moves up to 540,000 barrels per day of light crude oil, light synthetic crude, and natural gas liquids used to make propane. Roughly 80 per cent of this product originates in Alberta’s oilsands, with the rest coming from smaller deposits in the Midwest.

Completed in 1953, Line 5 was originally designed to bypass seasonal interruptions in oil tanker shipments across the Great Lakes.

“The ice cover on the lakes meant that they only got eight months a year of shipping,” said Jeffrey Insko, a professor at Oakland University in Rochester, Mich., who’s writing a book on the history of Line 5.