WASHINGTON – It will likely be months before investigators know what caused an ExxonMobil oil pipeline to rupture near Billings, Mont., spilling about 1,000 barrels of crude oil into the Yellowstone River, a federal safety official said Thursday.
Thus far, investigators are unaware of any safety violations by ExxonMobil related to the spill, Cynthia Quarterman, administrator of the Pipeline and Hazardous Materials Safety Administration told a congressional hearing. The spill has fouled shoreline and contaminated backwaters along dozens of miles of the scenic river.
The oil giant is working on a plan to lay a new section of pipe 30 feet below the river to replace the damaged pipe responsible for the spill, ExxonMobil Pipeline Company President Gary Pruessing said. The flow of oil through the pipeline has been shut off since the July 1 accident.
ExxonMobil hasn’t yet submitted its plan for the replacement pipe to the safety administration, which must approve the project before it can go forward, Quarterman told the House Transportation and Infrastructure Committee.
The agency hasn’t yet determined how deep the replacement pipe will have to be buried except that it will be deeper than the pipe that ruptured, she said. The depth will depend on the plan ExxonMobil submits, but horizontal drilling will be required, she said.
Federal regulations require that pipelines that cross underneath riverbeds be buried at least four feet, Quarterman said. The result of tests conducted by ExxonMobil prior to the accident indicated the pipeline beneath the river bottom was buried about five feet, she said.
At the time of the accident, unusually high amounts of mountain snowmelt had increased water level and velocity in the river to historic levels. That, in turn, increased the possibility for erosion of the riverbed covering the oil pipeline.
Safety officials were concerned enough about that section — as well as other pipelines in parts of the country that suffered flooding — that they were checking daily with ExxonMobil, Quarterman said.
It will likely be August or September before water levels in the river are low enough to exhume the section of damaged pipe responsible for the spill, she said. It will be about two months after that before investigators identify a cause, she said.
The pipe replacement will also require moving two shutoff valves, Pruessing said.
He also said he’s confident no more than 1,000 barrels of oil leaked into the river. Quarterman said her agency won’t know for certain how large the leak was until it examines records at the company’s control room in Houston.
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