The repair job ahead, including digging up and inspecting all caribou crossings under which the 34-inch crude oil pipeline is buried in the Prudhoe Bay oil field, will keep the pipeline out of service for another four to six weeks, said Maureen Johnson, senior vice president and manager of the Prudhoe Bay unit. The leak occurred in a section of pipe buried under one of the caribou crossings.

The state's chief economist for the Department of Revenue, Michael Williams, said March 15 that the state is currently losing nearly $1 million a day from the lost production. However, Williams said he agreed with BP officials that this was a deferral of production rather than a loss of oil, meaning the loss could be later recouped.

"What we have is a reduction in production due to a transportation issue. After the transportation issue is resolved, they'll go back to producing oil," he said.

Johnson said BP, the field operator, plans to meanwhile bypass that pipeline and transport the crude oil in about two weeks through a 24-inch pipeline, which can accommodate about 50,000 to 75,000 barrels of production daily from Gathering Center 2. The gathering station for the damaged pipeline normally produces 100,000 barrels daily.

"This is not something we are seeing in other places (in the Prudhoe Bay oil field)," Johnson said. "It's something we are seeing on this pipeline, and it's recent. There is something on GC-2 that is different."

BP representatives also said March 14 that its inspectors were aware of corrosion in the pipeline months before it burst, but believed the threat to be "manageable."

An inspection last fall revealed corrosion in the line and led officials to step up their schedule of inspections, Johnson said.

Johnson said corrosion was seen in the 34-inch oil transit line in a September inspection but it appeared to be occurring at a "low manageable corrosion rate."

Spill investigators also found significant damage - especially in low spots of the pipe - that likely occurred within the last six to nine months.

Johnson's comments came at a news conference at the BP Energy Center in Anchorage, called by BP and officials of the Alaska Department of Environmental Conservation.

"We believe the leak was caused by internal corrosion that happened relatively recently," she said. "We believe the leak probably started out as a pinhole and increased over time (under snow). The person who discovered the leak had to be standing right on top of it."

By the time the leak was detected on March 2, the hole in the pipe was one-quarter inch by one-half inch, she said. "We don't know and won't know when it started."

The spill, contained within a 2-acre area of the frozen tundra, is being cleaned up by removing liquid oil with a vacuum truck, plus removal of all contaminated snow and gravel.

Cause of the corrosion has not been determined, but BP said the company is looking into possible affects of lack of corrosion inhibitors, the new emulsion breakers being used at GC-2 and microbiologically induced corrosion.

"The new emulsion breakers are used at GC-2 to help us separate the viscous oil from the water and solids," said Daren Beaudo, a BP spokesman. "That was a unique chemical used there. Basically there has been a changing chemistry in the emulsion breakers. These are some of the things we are looking at (as possible causes for the internal corrosion).

"We are sensing that the corrosion inhibitors are not making it into the pipeline," Beaudo said. "When we start the 34-inch pipeline back up eventually, we are talking about injecting corrosion inhibitor into that line as a means of added protection. That corrosion inhibitor has not been carrying over into the pipeline because of some operational issues."

Between 201,000 to 267,000 gallons of crude oil are estimated to have been spilled from the pipeline, government regulators and BP said March 10 in a joint press release.

This would make the spill the largest crude oil release in the history of the North Slope, according to DEC.

The volume estimate was developed after surveyors probed the spill area to determine the oil thickness and verify the extent of the area affected, which is estimated at 1.9 acres.

Meanwhile, ultrasonic testing of a damaged section of the pipeline was completed late March 8, and a 6-foot-long metal sleeve was welded permanently into place March 10.

Cleanup operations continue around the clock in extremely adverse weather, with temperatures reaching minus 60 degrees to minus 70 degrees Fahrenheit with the wind chill.

The leak was discovered March 2 by a BP oil field worker, and the source of the leak was subsequently found to be a quarter-inch hole at the bottom of a section of pipe buried underneath a caribou crossing. Oil field pipelines are normally built above ground on steel supports on the North Slope to avoid melting the permafrost or permanently frozen soils. Short sections of pipelines are buried at strategic points to allow passage by large animals.

Meanwhile, ConocoPhillips Alaska Inc. reported a spill of produced water with traces of crude oil from a 24-inch pipeline in the Kuparuk River field on the North Slope, according to DEC. The spill was spotted by a ConocoPhillips field operator at 4:15 p.m. March 9 and was reported to the state DEC at 4:37 p.m.

ConocoPhillips Alaska Inc. is continuing to work at the site. Drill site 2M and 15 wells are still shut-in, with the loss of about 4,000 barrels per day. The company is cleaning the pipeline prior to making repairs, according to John Dixon, the state Department of Environmental Conservation official in charge of state oversight of spill cleanup. The produced water contains very little oil, but salt in the water is more of a concern because of possible adverse effects on the tundra, Dixon said.

Tim Bradner can be reached at tim.bradner@alaskajournal.com.

Margaret Bauman can be reached at margie.bauman@alaskajournal.com.