photo by: U.S. Environmental Protection Agency

A massive oil spill in north-central Kansas seeped into Mill Creek and traveled about three miles downstream. Cleanup crews contained the spill with a dam about four miles downstream.

The largest inland oil spill in nearly a decade has prompted the owner of the Keystone pipeline to build an earthen dam 3 miles downstream from the release in an attempt to limit the contamination in north-central Kansas.

Canadian company TC Energy also said it’s deployed some 250 workers to limit the damage from the pipeline’s rupture last week and the release of 14,000 barrels worth of crude — enough sludge to fill an Olympic-sized swimming pool.

Meantime, federal regulators said it appears the oil has not fouled groundwater.

TC Energy says it’s unclear how long it will take to clean up the damage and remediate the soil in Washington County, just south of the Nebraska border.

On Monday, its workers further surveyed the damage and prepared for rainy weather in the forecast. The pipeline company said it’s also conducting air quality checks, but it has detected no reason for public health concerns.

The company said it will continue cleanup efforts at the site until it is completely remedied and the pipeline will not restart until regulators say it’s safe.

“The health and safety of onsite staff and personnel, the surrounding community, and mitigating risk to the environment is our primary focus right now,” TC Energy said on its website.

The spill of roughly 580,000 gallons came with pipeline rupture last week that had residents waking up to an odor that smelled like petroleum.

Kellen Ashford, a spokesperson for the U.S. Environmental Protection Agency, said Monday the cause of the rupture will be determined by crews from the Pipeline and Hazardous Materials Safety Administration, which is part of the U.S. Department of Transportation. Officials for that agency did not immediately respond to a request for comment.

Ashford said the EPA has no timeline for TC Energy’s remediation efforts.

The oil had made it about three miles downstream in Mill Creek but was contained within the dam waterway. No groundwater has been affected, Ashford said.

“The only water that has been impacted has been the surface water in the creek,” the EPA spokesperson said. “The drinking water has not been impacted by the pipeline rupture.”

The type of oil in the Keystone pipeline is sludgy and often sinks to the bottom of waterways – making it more difficult to clean than conventional crude oil. The pipeline carries oil from Canada to American refineries. It has previously leaked in South Dakota and North Dakota, CNN reported.

TC Energy had planned to build an additional pipeline called the Keystone XL, which sparked years of political debate, legal wrestling and protests — primarily generated by environmental groups worried that expanding fossil fuels infrastructure would hurt efforts to fight carbon emissions and slow climate change. President Joe Biden blocked the XL pipeline immediately upon taking office.

— Dylan Lysen reports on politics for the Kansas News Service.