By Selam Gebrekidan
NEW YORK, Oct 11 (Reuters) - Initial investigationsfollowing a 20,600-barrel leak on Tesoro Logistics LP pipeline in North Dakota point to corrosion on the 20-year-oldpipeline, state regulators said on Friday.
The six-inch pipeline was carrying crude oil from the Bakkenshale play to the Stampede rail facility outside Columbus, NorthDakota when a farmer discovered oil spouting from the pipelineon Sept. 29.
This is the largest oil spill in the state since it became amajor U.S. producer. It is the biggest oil leak on U.S. landsince March, when an Exxon Mobil pipeline spilled 5,000to 7,000 barrels of heavy Canadian crude in Mayflower, Arkansas.
The release did not pose an immediate threat to groundwatersources or nearby rivers and lakes, the state Department ofHealth said on Thursday.
Initial concerns that the pipeline was punctured by nearbyresidents were dismissed and the cause appears to be corrosionon the pipeline, according to Brian Kalk, chairman of the statePublic Service Commission.
"It started out as a small hole and got bigger," Kalk said.
The U.S. Department of Transportation Pipeline and HazardousMaterials Safety Administration is in charge of investigatingthe cause of the leak and oversees the pipeline's operation.
But the state commission approves the construction ofpipelines and operators' compliance with initial designssubmitted to the state, Kalk said.
PHMSA and Tesoro could not be immediately be reached forcomment.
The pipeline, which runs 35 miles from Tioga to Black Sloughin North Dakota, was built by BP Plc in 1993.
It is a part of Tesoro's "High Plains" pipeline system inNorth Dakota and Montana that gathers oil from the Bakken shaleand delivers it to another Enbridge pipeline and Tesoro's 68,000barrels-per-day Mandan refinery.
Tesoro bought the pipeline and the refinery from BP in 2001.
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