Keystone is a major export pipeline carrying 622,000 barrels a day of crude from Alberta to U.S. refineries and was temporarily shut down in December after rupturing on Dec. 7 and leaking oil into a creek in Kansas. The pipeline resumed service in late December.

Clean-up work is ongoing and TC has not yet publicly identified the cause of the spill.

"We share the EPA's prioritization of safety and mitigating risk to the environment, and we are committed to complying with the agreement as we progress our response, recovery, and remediation," TC said in a statement.

"It is premature to surmise or speculate on costs."

In a clean-up order finalised on Jan. 6, the EPA said the leaked oil impacted water in the creek at least 3-1/2 miles downstream, stained vegetation, caused a visible sheen on the water and significantly affected fish and wildlife.

The order said TC must recover oil and oil-contaminated soil and vegetation and contain the further spread of oil the creek. All work must be completed under EPA oversight.

"The federal government and the state of Kansas are committed to a thorough cleanup and restoration of the impacted area," EPA Region 7 Administrator Meg McCollister said in a statement.

(Reporting by Nia Williams; Editing by David Gregorio)

By Nia Williams