An investigation is underway after oil was discovered on the ground along the Olympic Pipeline outside Anacortes.
A spokeswoman at the state’s Utilities and Transportation Commission told KIRO 7 indications are the pipeline is not actually leaking, and that the oil might have been on the ground for some time.
The pipeline owner, BP, said crews noticed about 60 gallons of diesel in a hole at the Allen Pumping Station.
The company said crews dug the hole weeks ago for maintenance but didn't have a chance to fill it in.
Then, last Wednesday, they noticed the oil, shut down the pipeline as a precaution, and began looking for a leak.
"We've been spending the time between then and now trying to get to the bottom of this thing," said Bill Kidd of BP.
Kidd said BP notified regulators and shut down the pipeline as a precaution.
Crews dug out around the pipe but couldn't find a leak.
The oil appears to be old, weathered diesel.
The state’s Department of Ecology told KIRO 7 the best theory right now is that it was left over from a 160,000 gallon spill at the pump station in 1988 and was flushed into the hole and a nearby monitoring well by last week's rain.
"It just does not appear to be fresh material," Kidd said.
The Olympic Pipeline sends all kinds of petroleum products from refineries in Whatcom and Skagit Counties to Seattle and Portland.
It also provides jet fuel to Sea-Tac Airport.
In 1999, an explosion on the pipeline killed three people in Whatcom County.
Since then, the state's Utilities and Transportation Commission has been regulating pipelines in Washington.
BP has owned the pipeline since 2001.
The pipeline fully resumed operations Monday afternoon.
No shortages have been reported.
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