Oil pipeline accidents have become increasingly frequent in the U.S. as Congress pushes for approval of the Keystone XL pipeline — a project that would pass near the spot where 30,000 gallons of crude spilled into Montana's Yellowstone River earlier this month.
The recent spill temporarily fouled a city's water supply and became the latest in a string of accidents to highlight ongoing problems with maintenance of the nation's 61,000 miles of crude oil pipelines.
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Yet in the politically charged debate over Keystone, its detractors aren't the only ones seizing on the Yellowstone spill. So are lawmakers who support the project.
In a floor speech Wednesday, Sen. John Hoeven, R-N.D., pointed to the Jan. 17 spill in Montana as an example of why new pipelines like Keystone are needed.
Keystone would be different than the half-century-old line that failed near the city of Glendive, Montana Sen. Steve Daines told The Associated Press.
"What this oil spill has done, is it makes clear that we need to be building the most technologically advanced and state-of-the-art infrastructure, pipelines like the Keystone," said Daines, a freshman Republican.
The number of significant pipeline-related accidents involving crude oil has been growing each year since 2009, reversing a decade-long declining trend, according to an Associated Press review of U.S. Department of Transportation records.
At least 73 such accidents occurred in 2014 — an 87 percent increase over 2009. Because of a lag in reporting by companies, the 2014 figure still could rise.
The tally includes accidents in which someone was killed or hospitalized, five or more barrels of oil were released, a fire or explosion occurred, or costs from the accident topped $50,000.
The increase came as surging domestic oil production boosted crude shipments by pipeline by about 20 percent, to 8.3 billion barrels annually, between 2009 and 2013, the most recent year available.
Meanwhile, pipes that were put in the ground decades ago are wearing out, said Rebecca Craven, program director for the advocacy group Pipeline Safety Trust.
Almost half the pipeline-related accidents since 2009 involved lines or equipment installed more than 40 years ago, according to records on more than 250 accidents that were reviewed by The AP and included age information.
Pipeline industry representatives say the increase in accidents is less straightforward than the federal data suggest.
An industry examination of crude oil and other hazardous liquid accidents in 2013 showed that in two-thirds of cases, the spill did not leave the responsible company's property, said John Stoody, vice president of the Association of Oil Pipe Lines. Most of the accidents involved fewer than five barrels, or 210 gallons.
The recent Montana spill was the second in less than four years on the Yellowstone, a largely untamed river that flows from Yellowstone National Park and across the breadth of Montana before feeding into the Missouri River in North Dakota.
The accident happened after a 120-foot section of Bridger Pipeline LLC's Poplar Pipeline became exposed beneath the river, increasing its vulnerability to underwater debris. The section that failed was installed in 1967.
The 12-inch steel line had been at least 8 feet beneath the river as recently as 2011, when a survey was performed in response to an earlier Exxon Mobil pipeline break beneath the Yellowstone.
For Keystone, project sponsor TransCanada plans to drill the 36-inch pipeline dozens of feet beneath major rivers to protect it from floodwaters or other outside forces.
Keystone's critics say no pipeline is entirely safe.
"You know what they say about pipelines? There's only two kinds: The ones that are leaking, and the ones that are going to leak," said Dena Hoff, a farmer and rancher whose property fronts the Yellowstone at the site of the Poplar Pipeline spill.
Keystone would move up to 830,000 barrels of oil a day. A break in the line could dwarf the recent Montana accident, on a line with a capacity of just 42,000 barrels daily.
TransCanada says Keystone would be buried deeply enough — at least 25 feet beneath the Yellowstone — to avoid even a 500-year flood event, said Keystone spokesman Shawn Howard. Precautions at 13 other major water crossings would be similar.
Yet even with the latest technologies, protecting pipelines beneath rivers presents challenges.
In 2011, days after flooding across the Northern Plains broke the Exxon pipe, U.S. Geological Survey researchers found "scour holes" as deep as 53 feet along the Missouri River.
While engineers have equations they can use to forecast locations where floodwaters may eat away at a river bottom, the USGS' Brenda Densmore said the dynamic nature of rivers can make them unpredictable.
"It's nature," Densmore said. "Is it going to follow the equation? I don't know for sure."