MARSHALL COUNTY, S.D. -- A total of 210,000 gallons of oil leaked Thursday from the Keystone Pipeline in Marshall County, South Dakota, the pipeline's operator, TransCanada, said.
Crews shut down the pipeline Thursday morning and officials are investigating the cause of the leak.
This is the largest Keystone oil spill to date in South Dakota, said Brian Walsh, a spokesman for the state's Department of Environment and Natural Resources.
In April 2016, there was a 400-barrel release -- or 16,800 gallons -- with the majority of the oil cleanup completed in two months, Walsh said.
About 5,000 barrels of oil spilled Thursday.
"It is a below-ground pipeline but some oil has surfaced above ground to the grass," Walsh said. "It will be a few days until they can excavate and get in borings to see if there is groundwater contamination."
There were no initial reports of the oil spill affecting waterways, water systems or wildlife, he said.
TransCanada said it was working with state and federal agencies.
"The safety of the public and environment are our top priorities and we will continue to provide updates as they become available," the company said.
The sections of pipeline affected stretch from Hardisty, Alberta, to Cushing, Oklahoma, and to Wood River, Illinois, the company said.
Environmental activist group Greenpeace said the spill shows another section of the pipeline in Nebraska should not be approved.
"The Nebraska Public Service Commission needs to take a close look at this spill," said Rachel Rye Butler of Greenpeace. "A permit approval allowing Canadian oil company TransCanada to build Keystone XL is a thumbs-up to likely spills in the future."