HOUSTON - Exxon Mobil Corp. delayed fully shutting down a ruptured oil pipeline in Montana's Yellowstone River in 2011, opening the door for an additional 1,000 barrels of crude to surge into the waterway, according to the U.S. government.
More than 1,500 barrels of oil flowed into the river after a July 1, 2011, failure in the 12-inch crude pipeline that runs from Silver Tip, Mont., to Billings, according to a report by the Pipeline and Hazardous Materials Safety Administration, a division of the U.S. Department of Transportation.
The report--dated Oct. 30, 2012, but released Jan. 2--said Exxon took reasonable precautions to prevent the spill and that Exxon Pipeline Company's controllers in Houston shut down some pumps and valves within 10 minutes.
However, another remotely controlled valve was allowed to remain open and continued to spew crude. The controllers debated for 46 minutes why pressure continued to drop in the pipeline before closing that valve. That delay "potentially" increased the size of the spill from 500 barrels to 1,500 barrels, the report said.
"Had [the company's] emergency shutdown procedures included the requirement that these [valves] were to be closed immediately after an abnormal event, the crude oil release volume would have been much less," the report states.
Exxon spokeswoman Rachel Moore said in a statement that the company "sincerely regrets that this incident occurred and is committed to learning from these events," adding that it would be "inappropriate" for Exxon to respond to the details of the report until the company has had more time to review the findings.
"We will continue to work cooperatively with the PHMSA on any follow-up actions."
The spill cost Exxon an estimated $135 million, including property damage, environmental remediation, and other costs.
The investigators wrote that they agreed with earlier findings that the pipeline was undermined by extensive flooding, which eroded the riverbed and exposed the pipeline to pressures it couldn't withstand. The report states that Exxon took "reasonable precautions" to address the flooding during the months leading up to the incident.
"Based on the lack of historical flooding impacts to this pipeline since 1991, [Exxon Mobil Pipeline Co.] may not have known that the river bottom could change sufficiently to undermine their pipeline," the report's authors wrote.
But the investigators concluded that controllers in Houston were only "generally aware" that there had been some flooding in Montana and hadn't been fully notified of conditions there or trained to handle problems that could be caused by excessive flooding, and as a result, the delay resulted in more oil flowing into the river than might have otherwise.
City officials in Laurel, Mont., expressed concerns about the pipeline and the potential impact of flooding in the weeks and months before the failure. Exxon temporarily shut the pipeline in late June, but later restarted it after visiting the site and reexamining its data.
Copyright (c) 2012 Dow Jones & Company, Inc.
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