By Selam Gebrekidan
NEW YORK, Oct 10 (Reuters) - A Tesoro Logistics LP pipeline spilled 20,600 barrels of crude oil into a rural field in North Dakota, the biggest leak since the Bakken shale oil boom made it the second-largest oil producing state in the United States.
The leak was first discovered on Sept. 29 in a low-lying hill 9 miles north east of Tioga, North Dakota, according to Kris Roberts, leader of the environmental response team with the state Department of Health.
The cause and duration of the spill was not yet clear, he added.
The leak did not pose an immediate threat to groundwater sources and there are no surface water bodies within a 5-mile radius of the spill, Roberts said.
San Antonio, Texas-based Tesoro Logistics said the affected segment of the pipeline remains shut. Repairs are underway and, along with containment and remediation work, could cost the company $4 million, the company said in a statement.
The pipeline was carrying crude oil pumped from the Bakken shale play, one of the most prolific gushers in the United States.
It was the biggest spill in North Dakota since 1 million barrels of salt water brine, a by-product of oil production, leaked from a well site in 2006, according to the state Department of Health. Another pipeline leak in 1989 also released large volumes of oil to the environment.
North Dakota produced more than 874,000 barrels per day in July.