The trans-Alaska pipeline remained shut down Wednesday as responders took a cautious approach to cleaning up crude oil that spilled into containment area.

North Slope oil production remains at a reduced level because of the pipeline problem.

Up to several thousand barrels of crude oil spilled Tuesday during a scheduled pipeline shutdown at a pump station near Fort Greely, about 100 miles south of Fairbanks. A spill of that size — totaling more than 100,000 gallons — would be one of the largest ever for the 33-year-old pipeline.

Power failed during testing of the pump station's fire-command system and a valve opened to prevent pressure from building too high in the main pipeline.

Oil flowed into a partially filled 2.3 million-gallon storage tank and then overflowed the tank into a large, bermed containment area, an outside yard underlain with an impermeable liner and surrounded by berm.

Alyeska Pipeline Service Co. evacuated the pump station and kept power shut off to avoid igniting volatile fumes.

This morning, Alaska Department of Environmental Conservation on-site coordinator Tom DeRuyter said crews determined it was safe to restore power to part of the facility but not yet to the spill tank.

The tank continues to leak oil into the containment area, but DeRuyter couldn't say how much. Alyeska last night estimated that continuing leak at about 5 gallons per minute.

"The oil is still in a containment (area) and there is no evidence of any leakage (outside of it)," he said.

Crews were able to go into the spill area this morning to stir the oil, DeRuyter said. That enabled them to estimate how much of the lighter components -- including benzene, ethylbenzene, toluene and xylene — had escaped from the crude and dissipated. Those lighter components are flammable and are known toxins that can be absorbed by the lungs and through the skin.

Alyeska is owned by an oil-company consortium and runs the 800-mile pipeline between the North Slope oil fields and the tanker port in Valdez. The pipeline daily carries about 650,000 barrels of oil production — roughly 10 percent of U.S. production.

The companies that own Alyeska and the pipeline are BP (46.9 percent), Conoco Phillips (28.3 percent), Exxon Mobil (20.3 percent), Koch Industries (3.1 percent) and Chevron (1.4 percent).

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