Investigators with the U.S. Coast Guard (USCG) and Spectra Energy are trying to determine how part of the company's Texas Eastern natural gas pipeline under the Arkansas River near Little Rock ruptured, leaving a two-mile stretch of the river closed to commercial traffic.
Spectra spokesman Creighton Welch told NGI that a 4.5-mile auxiliary pipeline, not the mainline, ruptured shortly after 9:30 a.m. on Sunday, May 31.
According to Welch, valves at both ends of the 24-inch diameter pipeline were closed and no gas was flowing through it at the time of the incident. The line was pressurized, but not in use. But the incident did cause an estimated 3.9 Mcf of gas to escape.
"The mainline seems to be operating normally under normal pressure," Welch said Wednesday. "We did go ahead and isolate the mainline -- closed the valves, just as a precaution while we're investigating whatever caused the failure of the auxiliary line. The mainline is currently shut down, but we have no indications of any damage."
Welch said the investigation continued Thursday with sonar surveys. “Divers did go into the water today, but the current proved too strong for safe operations,” he said. “Hazardous river conditions have hampered the pace of our investigation, and we will move forward in a manner that ensures the safety of our investigators.”
Welch said the mainline and auxiliary line run parallel, about 10 feet apart, and are both laid about four feet below the river bottom at the same depth.
USCG Lt. Brian Porter told NGI that two miles of the Arkansas River, between mileposts 116 and 118, remained closed to commercial traffic while it conducts its own investigation. Porter said the Jeffrey Sand Co. reported Monday that a towboat, the Chris M, was near the submerged pipeline at the time of the incident and had suffered some damage.
"It's still under investigation, and we don't know whether or not the pipeline was a direct cause of that," Porter said. "It's really in the infant stages of the investigation. We just know [the towboat] was in the vicinity."
Porter added that inspectors were sent to the area to conduct a casualty investigation. "From a USCG standpoint, there was no pollution found on the water," he said.
On Wednesday, Welch said investigators with Spectra "are not even certain that it was a boat that hit it. They're still trying to investigate that, as to what exactly might have caused this and obviously investigate whether the riverbed had shifted or anything like that. At the time, all of the barges were all docked and the river was closed because of high waters. We're still trying to figure out what exactly caused this."
But in a separate statement Thursday, Welch said “the incident was isolated to the river and there was some damage to one unmanned, docked tugboat.”
Welch said investigators cracked the valve on the north side of the river and saw bubbles about 100 feet from the north riverbank. The river is about 1,200 feet wide at the site of the incident. There were no evacuations or injuries. He added that the mainline is still shut down, and there was no estimate on when it would be returned to service.
"There were no taps that got shut in when we closed the valve with the mainline, so we're able to continue supplying gas to customers on both the north and south sides of the river," Welch said.