Last December, the Belle Fourche Pipeline in western North Dakota ruptured. At the time, the company estimated that 176,000 gallons of oil had been spilled before the pipeline was shut down.

But according to an updated estimate, the amount of oil that leaked from Bell Fourche was significantly higher, making it one of the largest pipeline spills in the state's history.

According to North Dakota's spill investigation program manager Bill Suess, the new estimate is that 529,839 gallons (or 12,615 barrels) of oil that have leaked out into the area around the pipeline. That's three times as much oil than was initially estimated, and that doesn't even include the hillside area of the spill, which Belle Fourche estimates could contain up to 20 percent of the spill's total volume.

Despite the bad news, spokeswoman Wendy Owen told NBC that the spill had been contained, and that 80 percent of the cleanup was already completed.

"There's no timeline for completion," said Ms. Owen, who works for True Companies, which owns the Belle Fourche Pipeline Company. "We will be there until it is [done]."

The leak occurred after the company shut the pipeline down on November 30 last year for routine maintenance after a heavy, wet snowfall. The weight of the snow caused a hillside to slump, and this, combined the absence of the usual pressure inside the pipeline, caused the pipeline to bend. One of the bends happened around a weld in the pipe, and the pipe cracked.

"That would explain why the leak detection didn't work," Suess told the Williston Herald. "(The electronic monitoring system) is gonna go take a baseline, but if the baseline is a leak, it's not going to catch it."

After the maintenance cycle was complete and the flow was turned back on, the pipe leaked for four days, from December 1-5. Because the leak was not detected electronically, officials had to visually estimate the amount of oil that had leaked, leading to the underestimation.

"The technology on gathering systems is always tricky," said Suess. "Unlike transmission lines, where there is a consistent volume from point A to B, with gathering lines you have have multiple points. There might be a point A, a point B, C and D, and all those different areas can be on or offline, so it's hard to measure the volume going through them because it's not consistent."

That can be a problem for many pipeline companies, particularly in North Dakota, where concerns about the negative effects of pipelines are at an all-time high, thanks in part to the native American protests against the North Dakota Access Pipeline for religious, political, and environmental reasons last year. The December spill took place less than 200 miles away from the main camp where most of these "water protecters" were based at the time.

"The spill gives further credence to our position that pipelines are not safe," said Tara Houska, a Native American environmental activist, in December. "Oil companies' interest is on their profit margins, not public safety."

North Dakota's recent oil boom has left the state particularly vulnerable to these kinds of failures. As The Christian Science Monitor reported last December on the state's largest ever oil spill:

More than three years ago, 840,000 gallons of oil seeped from a pipeline break in North Dakota to contaminate the surrounding soil. Less than a third has been cleaned up. .... The Sept. 2013 spill happened in a wheat field. A farmer noticed the smell of oil permeating the air for days on end, and the wheels of his combine became coated in the stuff. The farmer’s wife, Patty Jensen, told the Associated Press that the clean-up crews are working 24 hours a day, seven days a week. Yet Bill Suess, a North Dakota Health Department environmental scientist, worries that much of the oil may never be removed. "What happened to us happened and we can't go back," said Ms. Jensen. "But I get really upset when I hear of a new one and I wonder what is being done to prevent these spills."

Whenever a failure occurs, companies will put protective measures in place to prevent further leaks. But failures continue to crop up to strengthen the resolve of many who oppose them, despite pushback from the Trump administration's pro-pipeline policies.

"They can say they have all the latest technologies to safeguard against a leak," Standing Rock Sioux Chairman Dave Archambault II told NBC in December. "But when that leak happens, and it will, all those safeguards will go out the window."

So far, it is difficult to say how much damage the Belle Fourche spill has actually done. There are no cases of livestock or wildlife deaths that were shown to be directly related to the spill, though there have been some cattle deaths and one dead beaver in the vicinity of the leak. At the moment, cleanup efforts are being concentrated on Ash Creek Coulee, which is an important water source for cattle during grazing season, which starts on May 1. Cleanup crews have used over 1,200 controlled burns to eliminate the much of the oil on the water so far, said Suess.

"In situ burns are not new," he told the Williston Herald, "but it's the first time they've really done it on the water in North Dakota. They did one down in the Gulf with the BP spill."

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He added that this technique could be used to clean up future spills.

"Hopefully we don't have too many more like this, though," he added.