BILLINGS, Mont. — Delays in Exxon Mobil Corp.'s response to a major pipeline break beneath Montana's Yellowstone River made an oil spill far worse than it otherwise would have been, federal regulators said in a new report.
The July 2011 rupture fouled 70 miles of riverbank along the scenic Yellowstone, killing fish and wildlife and prompting a massive, months-long cleanup.
The damage could have been significantly reduced if pipeline controllers had acted more quickly, according to Department of Transportation investigators.
The report, provided by the office of Montana U.S. Sen. Max Baucus, marks the first time federal regulators have highlighted specific actions by Exxon as contributing to the severity of the spill.
An Exxon spokeswoman said Wednesday the company was reviewing the findings.
The spill released about 63,000 gallons of crude into the river near the city of Laurel. That damage would have been reduced by about two-thirds if controllers in Houston isolated the rupture as soon as problems emerged, investigators said.
Instead, as Exxon personnel weighed the appropriate response, crude drained from the severed, 12-inch pipeline for another 46 minutes before a control valve was finally closed.
Exxon spent $135 million on its response to the spill, including cleanup and repair work.
Spokeswoman Rachael Moore said the company will continue to cooperate with Pipeline and Hazardous Materials Safety Administration and "is committed to learning from these events."
The report chalks up the immediate cause of the spill to floodwaters that damaged the pipeline and left it exposed. Debris washing downriver piled up on the line, increasing pressure until it ruptured.
The "volume would have been much less," and the location of spill "would have been identified far more quickly" if Exxon's emergency procedures had called for the immediate closure of upstream valves, investigators said.
The report also faulted Exxon for lacking a plan to notify pipeline controllers that the river was flooding.
Exxon workers were not blamed, however, for steps taken in the lead-up to the spill.
Exxon's field observations and "depth of cover survey took reasonable precautions to address the flooding of the Yellowstone River it the spring and early summer of 2011," the investigators wrote.
City officials in Laurel had warned Exxon that the riverbank was eroding. The company, however, continued to run crude beneath the Yellowstone after finding that a section of pipeline leading away from the river was still buried more than 6 feet deep.
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