Investigators have ruled out the crude oil pipeline serving Unocal's King Salmon Platform as a source for a sheen seen intermittently near the platform in recent weeks.
Unocal resumed production from the platform Saturday evening, after the undersea oil pipeline passed hydrostatic pressure tests, said company spokesperson Roxanne Sinz. The pipeline again is carrying crude oil from the platform to Trading Bay on the west shore of Cook Inlet.
The sheen had been seen around the platform, often at slack low tide, for about two weeks before Sept. 12, when workers determined that the source was underwater and not on the platform as originally believed. On Sept. 13, Unocal stopped production from the platform and used seawater to flush the oil from the pipeline. Now, the pipeline has been ruled out as a source.
"Now, we're methodically trying to go through what the other possible sources might be," Sinz said.
She declined to speculate on the possibilities.
Workers from Cook Inlet Spill Response and Prevention Inc., the industry spill response group, sampled the sheen Saturday, Sinz said, but there was not much oil to collect. Since then, there has not been enough oil to sample at all. Unocal has hired an Anchorage lab to fingerprint Saturday's sample to help pin down a source.
Sinz said Unocal conducted side-scan sonar surveys of the area around the platform on Tuesday but found no likely source. Debris on the bottom interfered with the sonar, Sinz said. More sonar surveys were scheduled to be conducted Wednesday.
Gary Folley, an environmental specialist with the Department of Environmental Conservation in Soldotna, said tests on the Saturday sample suggest that the sheen is a product similar to No. 4 diesel, but Sinz said the composition of the leaking fuel has not yet been finally confirmed. Folley said he knows of no undersea pipelines carrying diesel near the King Salmon Platform. Fuel is delivered to the platform by ship, he said.
Unocal has provided the U.S. Coast Guard and DEC with a list of 20 possible sources for the sheen. Folley said the possibilities range from wrecked vessels to drilling muds and miscellaneous leaks.
Two undersea pipelines serve the King Salmon Platform, which was installed in 1967. One carries crude oil from the platform to Trading Bay.
The other carries natural gas from Trading Bay to the platform for fuel.
According to DEC, that also has been ruled out as a source. There could be no sheen from the gas line unless liquids were condensing within it, DEC said, and that is unlikely, since the line carries high-quality dry fuel gas. Since the pipeline operates at 400 pounds per square inch, a leak from the pipeline also would produce bubbles of gas, which have not been seen.
DEC workers have observed no wildlife oiled by the sheen. A CISPRI response ship, the Seabulk Montana, has stood by the platform during slack low tides, when the sheen seems generally to appear, and has used oil-absorbent materials when possible to recover oil.
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