Cleanup efforts underway after Keystone Pipeline spills estimated 3,500 barrels of crude oil

An estimated 3,500 barrels of crude oil spilled into an agricultural field in North Dakota after a Keystone Pipeline employee heard a "mechanical bang" from the system early Tuesday morning, managing company South Bow said. 

More than 200 people have been deployed to the site for oil recovery and remediation, South Bow said. A damaged section of the pipeline remains isolated. Officials previously said that a small stream near the area was not affected, but has also been isolated. 

As of Thursday, 700 barrels of oil, or about 20% of the amount spilled, had been recovered, the company said, adding that the system remained shut down.