Science

Thawing Permafrost Is Artificially Chilled to Stabilize Alaska Oil Pipeline

Thawing permafrost threatens to undermine the supports holding up an elevated section of the Trans-Alaska Pipeline, jeopardizing the structural integrity of one of the world’s largest oil pipelines and raising the potential of an oil spill in a delicate and remote landscape where it would be extremely difficult to clean up.

The slope of permafrost where an 810-foot section of pipeline is secured has started to shift as it thaws, causing several of the braces holding up the pipeline to tilt and bend, according to an analysis by the Alaska Department of Natural Resources. The department has permitted construction of a cooling system designed to keep the permafrost surrounding the vulnerable section of pipeline just north of Fairbanks frozen, as well as to replace the damaged portions of the support structure.

This appears to be the first instance that the pipeline supports have been damaged by “slope creep” caused by thawing permafrost, records and interviews with officials involved with managing the pipeline show.

In response, the Alaska Department of Natural Resources has approved the use of about 100 thermosyphons—tubes that suck heat out of permafrost—to keep the frozen slope in place and prevent further damage to the pipeline’s support structure.

“The proposed project is integral to the protection of the pipeline,” according to the department’s November 2020  analysis.

Alaska officials who oversee the pipeline have been unable to find any records of previous damage to the pipeline caused by slumping permafrost, or of the use of thermosyphons as a defensive safeguard once a slope has begun to slide, and could cite no incidents in which either of those things had occurred.

The installation of the heat pipes builds on an obvious irony. The state is heating up twice as fast as the global average, which is driving the thawing of permafrost that the oil industry must keep frozen to maintain the infrastructure that allows it to extract more of the fossil fuels that cause the warming. 

Any spill from the 48-inch diameter pipeline that flows with an average of 20 million gallons of oil a day, and the resulting clean-up activity, could accelerate the thawing of the permafrost even more, environmental experts said. 

The extent of the ecological damage would depend on the amount of oil spilled, how deep it saturated the soil and whether the plume reached water sources. But any harm from an oil spill would likely be greater than in most other landscapes because of the fragile nature of the Alaskan land and water.

“This is a wake-up call,” said Carl Weimer, a special projects advisor for Pipeline Safety Trust, a nonprofit watchdog organization based in Bellingham, Washington.

“The implications of this speak to the pipeline’s integrity and the effect climate change is having on pipeline safety in general.”

Weimer said this incident should trigger discussions between regulators and the industry about how to safeguard pipelines from the effects of thawing permafrost and other climate dangers.

“Science points to climate change getting worse. Now is the time to ask what’s being done about it,” Weimer said, referring to the effect of global warming on pipeline safety.

To safeguard the pipeline from possible collapse, the pipeline operator, Alyeska Pipeline Service Company, was granted permission earlier this year by the natural resources department to construct the passive cooling system to arrest the thaw of permafrost that is essential to locking the supports in the ground and keeping the slope from slumping or sliding. 

Alyeska is installing approximately 100 free-standing thermosyphons 40 to 60 feet into the ground. Construction is expected to take 120 days and will also include a three-foot layer of insulating wood chips atop the permafrost.

Industry Silence About an Increasing Threat

Michelle Egan, a spokeswoman for Alyeska, an association of oil companies that includes a subsidiary of Hilcorp Energy Co., as well as ConocoPhillips and ExxonMobil, declined to talk about the condition of the weakened section of pipe or the extent of permafrost thawing. Conoco deferred to Alyeska for comment; Hilcorp and Exxon did not respond to questions about the pipeline.

In its application to the state, Alyeska confirmed thawing permafrost posed a threat.

 “The purpose of this project is to protect the integrity of the Trans-Alaska Pipeline (mainline) from permafrost degradation,” the company’s application said.

Generally, Egan said, planning for and responding to changing permafrost conditions has been important to Alyeska since before construction of the pipeline in the mid-1970s.

“Permafrost changes were anticipated during the original design,” she said. “The construction mode and method of pipe support are designed to maintain the integrity of the pipeline and minimize impacts to the environment.”

To avoid problems with the permafrost, 420 miles of the Trans-Alaska Pipeline were built on an elevated support system that keeps the pipe about six feet above the ground. The frames that hold the pipeline, called vertical support members, look like a capital H with the pipeline resting on the cross stroke. Many of them have thermosyphons incorporated into the structure to keep the permafrost frozen. 

There are about 124,000 thermosyphons arrayed along the path of the pipeline—a nod from its engineers to the importance of keeping the ground below it frozen. The tubes are bored from 15 to 70 feet into the permafrost in areas where warming might cause it to thaw. But those chillers only cool the permafrost directly below the pipeline, which holds the supports. As the wider slope of permafrost surrounding the pipeline has warmed, the new thermosyphon project was required to keep it from collapsing or sliding and damaging the supports.

Tony Strupulis, the pipeline coordinator for the Alaska Department of Natural Resources, said there is no reason for panic—the support structures are not in immediate danger of collapse and the thawing of permafrost is a gradual process that allows time to address problems the defrosting might cause. Yet, he said, the agency is “very mindful” of the state of permafrost in relation to the stability of the pipeline and other infrastructure under its purview. 

“The design philosophy is, ‘If it’s frozen, keep it frozen,’” he said.

Temperatures that can thaw permafrost are more common in the region where the stabilization work is being done than in the Arctic, hundreds of miles to the north, he said. So the state depends on Alyeska’s maintenance crews to be especially watchful in those warmer areas, he said.

“If the support structures begin to sink or lean; that’s the big concern,” Strupulis said.

The section of shifting Trans-Alaska Pipeline is 57 miles northwest of Fairbanks near the Dalton Highway in the central part of the state, where mean annual winter temperature has warmed more than eight degrees Fahrenheit since 1949, according to data kept by the Alaska Climate Research Center.

About three quarters of the 800-mile pipeline, which opened in 1977 and runs from Prudhoe Bay in the north to Valdez on Prince William Sound in the south, passes through terrain with permafrost. Since opening, more than 18 billion barrels of oil have moved through the pipeline, a milestone that underscores its importance to the state’s economy and its role in meeting the energy demands of the country, as well as its part in driving the global warming that is thawing the ground that supports it.

Pipeline Plans Considered Permafrost Thaw, But Not Climate Change

Permafrost is ground that has remained completely frozen for at least two years straight and is found beneath nearly 85 percent of Alaska. Some permafrost, which is composed of a combination of soil, rocks and sand that are held together by ice, has been frozen for thousands of years. 

But, in the last few decades, permafrost temperatures in Alaska have warmed as much as 3.5 degrees Fahrenheit, and the state’s average temperature is projected to increase by 2 to 4 degrees more by the middle of the century. A study published in the journal Nature Climate Change projects that with every 2 degree increase in temperature, 1.5 million square miles of permafrost could be lost to thawing. 

The pipeline was built to flex and absorb some movement, especially from seismic activity, without failing. Engineers and pipeline consultants praise it for its “robust” safety design.

In the event of a rupture in the pipe, Alyeska said it can initiate an emergency shutdown to stop the flow of oil and isolate the damaged section of pipeline within 15 minutes.

There have been 18 breaches of the Trans-Alaska Pipeline in the last 20 years, according to data from the Pipeline Hazardous Material Safety Administration (PHMSA).

Spills have ranged from less than one barrel to 6,800 barrels. In all, the pipeline has spilled 9,784 barrels of oil, which resulted in $52.7 million in damages and costs, according to the PHMSA records.

Causes of the spills range from breaks in corroded pipe to equipment failure and operator error. None of the spills recorded by PHMSA were attributed to permafrost thaw.

Clean-up of a spill along the pipeline would also threaten to accelerate more permafrost thawing, Alyeska said in its emergency response plans filed with federal and state regulators. 

“Thermal erosion can occur at any time during a discharge, containment, recovery, and final cleanup period,” according to the company’s plan. “This geological condition should not impact response actions but may affect efficiencies and the methods used to perform containment and recovery actions in order to protect permafrost areas from long term damage.”

Alyeska recognizes permafrost can act as a barrier to the spread of spilled oil just as it has acted for decades to prevent the release of toxic substances from Alaskan landfills, former military installations and a Superfund site.

“Permafrost can be a containment asset as it prevents downward migration of spilled oil,” the company said in its response plan.

Many of the pipelines in Alaska were designed decades ago, accounting for the permafrost projections that are now far short of the reality in which annual temperatures are soaring and thousands of square miles of permafrost are thawing.

Richard Kuprewicz, president of Accufacts Inc., a pipeline consulting firm, said it wouldn’t be wise for pipeline operators to count on permafrost remaining solid in the same way as in the past.

Assessing pipelines to determine if years-old structural designs can withstand the changing conditions and accelerated rate of permafrost thaw is prudent, he said.

“Operators need to understand this new world being brought about by climate change,” he said.  “What was true in the past may not be true today.”

So it’s the responsibility of the operator to be ahead of the threats, Kuprewicz said.

“It’s not yet to the level of panic, but it is an issue that has to be considered,” he said.

Tom DeRuyter, a former on-scene spill coordinator for the Alaska Department of Environmental Conservation, has observed the effects of thawing permafrost for decades.

He’s seen the vertical support structures of pipelines sinking, he said, and noticed that such movement has accelerated as temperatures have warmed.

“The fact is there is a problem with subsidence,” said DeRuyter, who retired last year after 24 years with the state agency. “You have pipelines that were built level and are now starting to wobble.”

DeRuyter, who emphasizes he is not an engineer and cannot comment on the potential threat to the structural integrity of the sagging pipelines, said his assessment is based on his observations.

“You see it pretty much on all of the pipelines,” he said. “You drive down the road and it looks like the pipelines are undulating.”

While the thawing and subsidence are usually too gradual and incremental to draw attention, the result is increasingly obvious, he said. 

“You can’t see it day-by-day, but year-by-year you notice these pipelines aren’t straight anymore,” he said.

Although there have been no documented instances of thawing permafrost causing a pipeline failure, in June 2020, it was blamed for the collapse of a fuel tank in northern Siberia that dumped 21,000 tons of diesel, which spread over seven miles and seeped into the Ambarnaya River. The second worst oil spill in modern Russian history, Norilsk Nickel, the owner of the plant, reported in a statement that permafrost thawing during a historic Siberian heat wave led one of the tank’s support pillars to buckle. Russian environmental authorities estimated it will take 10 years to clean up the spill.

This story originally appeared in Inside Climate News and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.

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