Canada's approval last week of an oil export project that could also create a seven-fold increase in tanker transits is drawing scrutiny from a US senator concerned about potential oil spills.

Maria Cantwell, a Democrat from Washington state, sent a letter to President Obama and US Coast Guard Commandant Paul Zukunft with regard to the Trans Mountain Pipeline.

Canada's Prime Minister Justin Trudeau signed off on the Kinder Morgan-backed project, which will triple the volume of crude oil carried from Canada's oil producing province of Alberta to British Columbia.

The approval also includes a permit for the Kinder Morgan-owned Westridge Marine Terminal to increase the number of tanker transits it can receive from five to 34 per month.

Cantwell says the approval of the project "did not take into account the risk posed to the United States" in terms of the increase in tanker transits in the mutually shared Strait of Juan de Fuca and Salish Sea.

A spill in that region "could restrict vessel traffic to such a degree that our ports could be brought to a grinding halt," Cantwell said in the letter.

The senator added that an oil spill response for the heavy Canadian crude oil which will be shipped out of the port is not adequate at the current time due to little study as to how heavy crude acts in the environment. The Oil Spill Liability Trust Fund, an $0.08 per barrel excise tax on US crude oil, currently does not cover heavy oil, Cantwell noted.