Spectra Energy said Monday that it still does not know what caused its natural gas pipeline in the Arkansas River to rupture May 31 but considers the river's flooding a factor.
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Spectra Energy is preparing to pull part of the broken pipeline from the river to inspect it and determine a cause, spokesman Phil West said.
"I know the team is looking at the river current and the recent current situation as one of the factors," he said, adding that he didn't want to speculate on the cause of the rupture until the company knows what happened.
Spectra Energy's 24-inch pipeline released 3.9 million cubic feet of natural gas into the Arkansas River when it ruptured about 9:30 a.m. about 1 mile east of the Interstate 30 bridge.
The 63-year-old pipeline is part of the Texas Eastern Transmission system, which crosses the river between Little Rock and North Little Rock.
The line that failed is a backup pipeline to the system's main transmission line, which runs from Texas to New Jersey. The parallel lines are about 10 feet apart.
The primary transmission line, which serves CenterPoint Energy, was operating normally after the other line ruptured, but Spectra Energy shut it down as a precaution.
"We don't have a schedule for returning the main line to service, but we're going to make sure it's in good operating condition when we do," West said.
Spectra Energy is waiting for the flooding river's currents to ease before crews begin removing parts of the pipeline, but the company could start the recovery process as early as today, West said.
The main part of the pipeline the company is looking to extract from the river is a 400-foot section that detached when the line burst and was pushed downstream.
The section of pipe showed up on sonar scans conducted by Spectra Energy last week on the north side of the river, about 100 feet from the line's original crossing.
The backup pipeline is 41/2 miles long. The Arkansas River, where the pipeline crosses, is roughly 1,200 feet wide, according to Google Earth.
To remove the separated section of pipe, along with other parts that are of interest but still connected to the pipeline, Spectra Energy will cut the pipeline into "manageable pieces," West said.
Some cuts will be made underwater, with additional cuts being made once the pipeline is placed onto a barge.
A 2-mile section of the river that was closed last week as Spectra Energy investigated the rupture reopened about 7:30 p.m. Friday, said Lt. Brian Porter, spokesman for the U.S. Coast Guard in Memphis.
"It's been deemed safe to proceed with caution," he said about the section of the river that runs from mile marker 116 to 118.
Spectra Energy has said no residual natural gas was left on the river and that the gas released would have dissipated.
While water can become flammable from natural gas, the quick rupture of the pipeline means any gas released quickly dissipated into the atmosphere, said Laura Ruhl, assistant professor in the department of earth sciences at the University of Arkansas at Little Rock.
She said the release of the gas adds to the amount of greenhouse gases in the air. "I don't think there is a lot of lasting environmental impact from the pipeline rupture," Ruhl said.
She said the pipeline burst would have been more dangerous if someone was traveling the river at the time or if it happened in a populated area.
"It is a volatile and explosive gas that could have been a problem at the time," Ruhl said. "I think it was fortunate that not many people were around. Had someone been right over it, there might have been damage and injuries as well."
Phillip Wallace, a representative for Pipeliners Local Union 798 in Bald Knob, said many older pipelines need to be replaced.
"Back in the day when these lines were put in, they would dredge these rivers," he said. "The high waters could bring the line up."
The pipelines would be coated in concrete to weigh them down as the pipes were placed about 6 to 10 feet under the riverbed in trenches, Wallace said.
Spectra Energy used this method when it placed the pipeline in a trench across the river in 1952.
The concrete-coated pipeline was then covered in river mud and sand, with the company maintaining and inspecting the coverage, Spectra Energy said.
"Of course, over the years that bottom ... it washes the silt and everything around, and evidently this one wasn't very deep," Wallace said, adding "[Spectra's] pipeline, I say, it's done forever. They'll have to abandon that."
The company said it last had divers check for exposed sections of pipe in 2011 and no problems were found. At the time, the minimum coverage over the pipeline was about 4 feet.
"Trenching is still something we do," West said. "It really depends on the situation, on how you approach the specific water body you are trying to cross."
A more recent method of running a pipeline under a river involves horizontal drilling, said Wallace, who has helped place pipelines using both techniques.
Through the process, the pipeline is gradually angled beneath the river and pushed across.
By doing this, the pipeline's ends are far from the bank of the river and at least 50 to 60 feet below the riverbed, Wallace said.
CenterPoint Energy recently used this method to install a natural gas distribution line under the Arkansas River.
Alicia Dixon, spokesman for the company, said that while the technology was developed in the 1970s and 1980s, it became more common in the 1990s.
"Prior to this horizontal drilling technology, natural gas distribution lines that needed to cross large waterways were attached to bridges," she said, adding that CenterPoint Energy has another distribution line crossing the river attached to the Interstate 430 bridge.
Metro on 06/09/2015