Nebraska state officials said Friday an oil spill from the Keystone pipeline in South Dakota won't affect their imminent decision to approve or deny a route for the related Keystone XL project, proposed by TransCanada Corp.

The decision will be based solely on testimony and documents during public hearings over the summer and from more than 500,000 public comments, Nebraska Public Service Commission spokesperson Deb Collins said.

Meanwhile, a Pipeline and Hazardous Materials Safety Administration representative from the federal government said Friday that the agency's investigation into the estimated 795,000-litre oil spill is ongoing.

TransCanada Corp. crews shut down the company's Keystone pipeline Thursday after a drop in pressure was detected from the leak south of a pump station in Marshall County, near the North Dakota border.

A South Dakota official says there was a roughly five-hour lag between TransCanada Corp.'s detection of the leak from its and its notification of state environmental officials.

Brian Walsh, an environmental scientist manager at the South Dakota Department of Environment and Natural Resources, said officials would likely look into the notification gap to determine if there was an appropriate reason.

TransCanada said Friday about 75 crew members, as well as state and federal officials, are on site near Amherst, S.D., with a full complement of cleanup equipment to contain the spill in a farmer's field.

The company said it has observed no further environmental impacts and no threat to public safety, though the nearby Sisseton Wahpeton Oyate of the Lake Traverse Reservation has expressed concern the spill might contaminate water supplies.

Keystone XL map March 2017

The Keystone XL pipeline would bring oil from Hardisty, Alta., to Steele City, Neb. (Natalie Holdway/CBC)

The existing Keystone pipeline transports crude from Alberta to refineries in Illinois and a major storage hub in Oklahoma, passing through the eastern Dakotas, Nebraska, Kansas and Missouri. It can handle nearly 600,000 barrels daily, or about 8.7 billion litres.

The Keystone XL expansion has been fiercely opposed by environmental activists, Indigenous tribes and some landowners.

President Donald Trump issued a federal permit for the expansion project in March even though it had been rejected by the Obama administration.

A Nebraska law approved in 2011 prevents the commissioners from factoring pipeline safety or the possibility of leaks into their decisions.

Lawmakers argued at the time that pipeline safety was a federal responsibility that pre-empts state law, but opponents blasted the restriction, saying politicians caved to lobbyists.

'We would have had so much crud and chemicals'

Some state residents are very concerned by the latest development.

"Pipelines are basically plumbing; and plumbing leaks. It comes as no surprise," said Tom Genung, who lives near the proposed route in Holt County, Neb.

Art Tanderup's family farm in Neligh, Neb., is in the path of the project. He said he hoped the spill in South Dakota will help sway any of the five Nebraska commissioners who may be on the fence about whether to issue a permit to TransCanada.

"I hope it sends a message to those five people making that decision on Monday," said Tanderup.

He said the proposed XL pipeline would be built over huge swaths of porous, sand-like soil atop the Ogallala aquifer, putting farmers and ranchers at risk of water contamination if a spill occurs.

"If that happened on our farm, we would have so much crud and chemicals in the Ogallala aquifer that we could never clean up," he said.

Greenpeace called on the Nebraska government in a statement Friday to reject the plan, saying "the writing on the wall to reject this pipeline could not be more clear."

"These pipelines are bound to spill, and they put communities, precious drinking water, and our climate at risk. An approval of yet another pipeline is a mistake," said Rachel Rye Butler from the organization.

"A permit approval allowing Canadian oil company TransCanada to build Keystone XL is a thumbs-up to likely spills in the future. The company does not have a clean track record of preventing spills, so why should they be able to build more pipelines?"

The statement ended with a call to governments to invest in clean energy.

With files from CBC News, Canadian Press and Reuters