Nov 1 (Reuters) - Cleanup crews in Walsh County, North Dakota, are starting work to plug the Keystone pipeline, which was shut after a more than 9,000-barrel crude oil leak this week, a state official said on Friday.
The work on the underground pipeline, owned by TC Energy Corp, is intended "to prevent any further oil that may be sitting in the pipeline from being released," said Karl Rockeman, director of the North Dakota Division of Water Quality, whose department is overseeing the cleanup.
It is still unclear what caused the leak, which occurred near a TC Energy pumping station, Rockeman said. The spill, first detected by TC Energy on Tuesday night, saturated an area about half the size of a football field and affected a wetland, the company and state officials said.
The 590,000 barrel-per-day (bpd) Keystone system is a key transporter of Canadian crude from northern Alberta to refineries in the U.S. Midwest. Its closure has forced TC Energy's Marketlink pipeline from the Cushing, Oklahoma storage hub to Nederland, Texas, to reduce rates.
Canada is the biggest provider of foreign oil to the United States, with U.S. exports averaging about 3.6 million bpd in 2018, according to the federal Canada Energy Regulator. Much of that oil is heavy crude, which is blended with other oils for processing into gasoline, diesel and other fuels.
About 60 percent of Canada's U.S. exports go to the Midwest.
The leak took place in a rural area close to the small city of Edinburg in the northeast part of the state. Rockeman said workers will start cleaning the area by pumping oil off the ground surface.
Reporting by Laila Kearney; Editing by Dan Grebler