The TMEP would draw heavily on supply from the Alberta tar sands in Canada. These bitumen deposits require a lot of effort to extract, recover and pre-process before the oil can be sent to conventional refineries. Most of the current extraction process takes place in open-pit mines, with massive machinery scraping up the tarry sandstone and moving it to facilities for processing. The heavy crude is found mixed with sand, clay, and water, which must be removed, then the heavy crude must be "upgraded" to reduce viscosity and improve quality (sources The Atlantic, Greenpeace). This process has destructive impacts on the land and means a heavy carbon footprint during the laborious extraction and upgrade process, as well as massive amounts of toxic byproducts. Studies show oil sands crude emits more greenhouse gases than conventional crude oil.

In 2014 production of tar sands in Alberta was 2.3 million barrels/day ( www.energy.alberta.ca). This expansion will carry an extra 590,000 b/d (i.e. a quarter of current production), and “companies operating in the oil sands have approvals to produce over 5.2 million barrels of oil per day” (credbc.ca).

The original Trans Mountain Pipeline has a controversal history of oil spills. In the period 1961-2016 there were 81 reported incidents, including:

• Abbotsford 2005: A ruptured pipeline dumped 210 cubic metres of crude oil. The company attributed the accident to activity in a neighbouring property.
• Burnaby 2007: A contractor working on a sewage project for the City of Burnaby ruptured a pipeline, causing spillage of 224-234 cubic metres of crude oil, some of which flowed into Burrard Inlet via the Burnaby storm sewer system; most of it was recovered. Eleven houses were sprayed with oil, and about 225-250 residents were evacuated or left voluntarily. Cleanup took more than a year. Source: report by the Canadian Transportation Safety Board.
• Burnaby 2009: 305 cubic metres of crude oil were released from a tank in the Trans Mountain Burnaby Terminal, most of it flowed into a containment area.
• Sumas 2012: 90 cubic metres of light crude oil leaked from a Sumas Mountain holding tank, all of it flowed into a containment area.

The existing and proposed pipelines ship diluted bitumen through the Strait of Juan de Fuca, an extremely sensitive environmental region. The tankers have to pass through a very narrow channel of shallow water to reach the open sea, making the project controversial and strongly opposed, for reasons similar to the opposition to Keystone XL, Line 9 and Northern Gateway, as well as offshore deep ocean oil drilling.

A July 2017 Greenpeace report concluded: oil spills anywhere pose serious risks to human health and the environment, and oil spilled into bodies of water is difficult to fully clean up. Diluted bitumen transported from Canada’s tar sands fields represents a particular threat to water resources along the routes of proposed pipelines.

The expansion of the Canadian tar sands, from which this project derives its oil, would lead to increased destruction and poisoning of the lands, waters and air of the Indigenous Peoples directly on the front lines and downstream of the tar sands. Furthermore, the communities would be threatened by more possible oil spills from the pipelines, trains and tankers (source: Treaty Alliance).

This project does not have the Free, Prior and Informed Consent (FPIC) of the Indigenous people it will affect. First Nations tribes that would be directly impacted by the route and port terminal are fighting the project in the courts and leading heated protests on the ground. The Tsleil - Waututh, Squamish, Musqueam, and Sto:lo First Nations, whose territories cover most of Metro Vancouver Area, are among the nine First Nations and Tribes currently in litigation against the project. The Coast Salish, Sto:lo, Nlaka'pamux, and Secwepemc Nations, whose territories cover more than half the length of the pipeline, have also filed legal challenges to the project.

As with the Dakota Access Pipeline, a highly controversial project constructed without FPIC of the Standing Rock Sioux Tribe and other affected tribal nations that source their drinking water from the Missouri River, the Trans Mountain Pipeline expansion also poses a grave threat to Indigenous People, as described in this letter written by several NGOs and groups of Indigenous people to 28 banks involved in financing this project.

Mike Hudema, climate energy campaigner at Greenpeace Canada, stated: “Not only have First Nations not given their consent but they have said very strongly that they don’t want these pipelines going through their traditional territory.”