The leak, which occurred northwest of Edinburg, North Dakota, affected a wetland area, Karl Rockeman, director of the state's Department of Environmental Quality's division of water quality, said in a statement.
The Keystone project was vigorously opposed by environmental groups and activists, from New Jersey progressive Lisa McCormick to actress Shailene Woodley, who was arrested during a 2016 protest at the pipeline.
Crews shut down the pipeline after the leak was discovered, but an estimated 9,120 barrels of oil were released into a wetlands area, officials said. The company did not specify if the entire pipeline was shut down or just a portion. It has experienced problems with spills in the past, including one in 2011 of more than 14,000 gallons of oil in southeastern North Dakota, near the South Dakota border.
Another massive spill along the Keystone pipeline has prompted outrage from activists who are now in opposition to the Keystone XL expansion that was first rejected by former President Barack Obama but given allowed by a permit from President Donald Trump. While the extent of damage remains unknown, Keystone's 2017 spill was revised from an initial estimation of 210,000 gallons to more than 400,000, leaving critics concerned about the environmental damage the leak may have caused.
State Environmental Quality Chief Dave Glatt said no sources of water were affected by the spill.
The $5.2billion Keystone has leaked substantially more oil, and more often, in the United States than the company indicated to regulators in risk assessments before operations began in 2010, according to a Reuters review in 2017.More news: Rudy Boesch, contestant on first season of 'Survivor,' has died
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"Our emergency response team contained the impacted area, and oil has not migrated beyond the immediately affected area", TC Energy said.
It's created to carry crude oil across Saskatchewan and Manitoba, and through North Dakota, South Dakota, Nebraska, Kansas and Missouri on the way to refineries in Patoka, Ill. and Cushing, Okla.
It said the West Path project is underpinned by about 260 million cubic feet per day of new firm service contracts with terms that exceed 30 years, starting in late 2022. The federal Pipeline and Hazardous Materials Safety Administration is leading the inquiry at the site, Rockeman said.
The company said net income came in at $739 million for the quarter ending September 30, compared with $928 million for the same quarter a year earlier.
Democratic presidential candidate Bernie Sanders took to Twitter on Thursday to condemn the pipeline and Trump for supporting the extension of it.
"This is exactly the kind of spill we are anxious about when it comes to the Keystone XL being built".