Spill Alerts Rang, Dismissed As False
By Wesley Loy, Anchorage Daily News, Alaska
Apr. 21–A pipeline leak-detection system sounded warnings on four straight days in the week leading up to last month’s record North Slope oil spill, but field workers interpreted the signals as false alarms, a new investigative report says.
The report, prepared by a team of BP and state investigators, confirms that the leak from a large Prudhoe Bay oil field pipeline went on undetected for at least five days “and probably much longer.”
The highly technical, 125-page report also suggests that the pipeline’s leak-detection system is effective only in catching leaks that release large volumes of oil rapidly. It doesn’t work well in detecting small, slow leaks that over time can result in large spills.
A Prudhoe Bay worker driving along the pipeline discovered the spill March 2 after catching a whiff of petroleum in the air.
Spill responders estimate 201,000 gallons, or 4,790 barrels, of oil oozed over almost 2 acres of snow-covered tundra and the edge of a frozen lake. Corrosion was blamed for eating an almond-sized hole in the steel pipeline, which remains out of service for repairs.
The line is a major artery in the web of pipes that drain the Prudhoe Bay field, the nation’s largest.
BP this week presented the investigative report to the state Department of Environmental Conservation, which continues to weigh a fine or other penalties against BP. The U.S. Environmental Protection Agency also is conducting a criminal investigation, BP spokesmen have said.
The seven-member investigative team included BP managers and engineers based in Alaska as well as Houston, BP attorney Randal Buckendorf, a Prudhoe field worker representing the United Steelworkers union, and Gary Evans, a DEC environmental specialist.
The report says that on four consecutive days, Feb. 25-28, the pipeline’s leak-detection alarms went off “but were ruled out as a spill” after people monitoring the system considered a variety of technical factors.
For one thing, a leak should have been indicated by readings on an adjoining segment of the pipeline, but that wasn’t the case, the investigators found.
Other factors also made the three-mile pipeline prone to false leak alarms, the report says. The oil flowing through it had a relatively high level of sediment, and the amount of oil moving through the line can fluctuate depending on output from an upstream oil processing plant.
All those factors create “noise” that can mask indications of an actual leak, especially a small one, the report says.
Under state regulations, the pipeline’s detector is supposed to be able to spot a leak amounting to 1 percent or more of daily throughput. The leak was too much of a trickle to hit that trigger, the investigators found.
Still, the leak detector emitted alerts because it was set on high sensitivity to detect a leak as small as 0.5 percent of daily throughput.
Engineers and other workers who monitor the system were aware of the warnings but determined the alarms were false, the report says.
It stops short of blaming anyone for the spill.
A $6 million cleanup of the oiled tundra is essentially complete, and DEC officials say they believe environmental damage to the tundra will be minimal.
Taking the leaky pipeline out of service for weeks caused North Slope oil production to decline by as much as 12 percent or 100,000 barrels per day, but BP says it has restored most of that production by routing oil down other pipelines.
Federal pipeline regulators have ordered BP to closely inspect the leaky pipe and two other major trunk lines to look for potential trouble spots. They also ordered the company to step up the use of pigs — bullet-shaped devices that slide through pipelines to look for corrosion or to swab out sludge.
The above-ground pipeline leaked at a point where it passed through a mound of gravel known as a caribou crossing, which works as a sort of bridge for the migratory animals. In 1998, a pig run identified six spots at the caribou crossing where corrosion was chewing pits into the pipe’s inner wall. One of those six was where the oil leaked, the report says.
BP had not done another pig run since 1998 to test for internal corrosion.
Maureen Johnson, a BP senior vice president, has said the company plans to work with the DEC on ways to detect smaller spills that might evade leak detectors.
One idea, she said, might be to increase the use of aerial infrared surveys, which can spot warm oil obscured by snow.
BP runs Prudhoe and owns 26 percent of the production. The biggest Prudhoe owners are Exxon Mobil and Conoco Phillips, each with about 36 percent.
BP SAFETY: The chairman of BP, Peter Sutherland, told investors Thursday that the company had learned valuable lessons.
SPILL REPORT AT A GLANCE
BP and the state released joint findings Thursday on what led to the 201,000-gallon oil spill at Prudhoe Bay discovered March 2:
–A pipeline leak detector warned of a possible spill four times before March 2.
–Field workers interpreted alarms as false.
–The corroded spot where the pipeline hole developed had been known of since 1998.
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