The Alaska Department of Environmental Conservation said Unocal's King Salmon platform in Cook Inlet is back in operation and a side-scan sonar survey is scheduled to be run today in a continuing search for the source of a sheen near the platform.
Unocal responded to a sheen in the vicinity of the McArthur River field platform by shutting in the platform and hydrotesting an 8-inch subsea crude oil pipeline which carries oil from the platform to the Trading Bay production facility on the west side of Cook Inlet.
DEC said Sept. 13 that droplets of oil had been observed adjacent to the platform for about two weeks, but the source had been believed to be equipment on the platform. The afternoon of Sept. 12, however, it was determined that the source was subsea.
The amount and type of oil are unknown. It appears to be bubbling up from a subsea source adjacent to the platform on an intermittent basis. DEC said the bubbling is underneath the flare boom, but the source appears to be beneath the water surface. The oil bubbling was observed at 10:20 Sept. 13 and appeared to stop 50 minutes later, producing a sheen approximately 20 feet by 400 yards.
Unocal Alaska spokeswoman Roxanne Sinz told PNA Sept. 13 that the sheen is very small and is just north of the platform. It was spotted at 10:20 a.m. and Unocal began work to shut in the platform and planned to begin hydrotesting the oil line that same day.
On Sept. 14, Sinz told PNA, there was another small sheen in the vicinity of the platform. The oil line had been displaced with water and Unocal was preparing for a second displacement, which would be followed by a hydrotest. She said the source was still unknown, the quantity was still unknown and Unocal was continuing to investigate.
DEC said today that a successful hydrotest on the crude oil pipeline was completed Sept. 15 and the pipeline was deemed fit for service. DEC said Unocal returned the platform to production after consultations with DEC and the U.S. Coast Guard.
DEC said the sheen is an unknown oil type, although initial sample analysis indicates that the product is similar to a No. 4 diesel. Oil still appears to be bubbling up from a subsea source adjacent to the platform on an intermittent basis.
Cook Inlet Spill Prevention and Response Inc. response vessel Seabulk Montana has been activated and positioned at the platform during low slack tides, which is when the sheen has generally been visible, and response vessel crews are recovering oil using sorbant sweep when possible and are also collecting samples.
DEC said that Unocal has provided DEC and the Coast Guard a list of 20 possible sheen sources in addition to detailed plans for investigating each potential source until the source is determined. A side-scan sonar survey of the seafloor at the platform was scheduled for Sept. 18.