Officials have found a 24-inch jagged rupture in a pipeline that began pouring oil and water Nov. 29, creating one of the biggest North Slope crude oil spills ever.
The on-scene coordinator for the state Department of Environmental Conservation, Tom DeRuyter, said Tuesday that the breach on the bottom of the pipe was the biggest he had ever seen and indicative of the incredible pressure the pipeline was under when it split.
Workers located the source of the leak Monday after cleanup crews hauled away spilled crude and contaminated snow and ice that had been obscuring the area.
Officials say massive ice plugs had formed inside the pipe, which caused BP Exploration (Alaska) Inc. to stop operating it a few weeks ago. Pressure then built up until the pipeline ruptured, according to BP.
"It looks like it was caused by overpressure in the pipe, which we think was linked to ice forming -- the plugs that have formed on either side of the release site," BP spokesman Steve Rinehart said.
Most likely, rapidly forming ice plugs began to grow toward one other, creating a high-pressure area in between, DeRuyter said.
"When a line does that, it rips out with a pretty impressive force and with a very large hole."
As for the specific circumstances that caused the line to fail, those are still under investigation, Rinehart said.
The working estimate of the spill's size is about 46,000 gallons of crude and produced water, the oily water pumped up from the well. The line is no longer leaking. Cleanup operations are well under way, according to state and federal officials.
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