Rufous52/iStockphoto/ThinkstockAn estimated 20,600 barrels of crude oil have spilled into a field in North Dakota from a pipeline operated by Tesoro Logistics LP, Reuters reported.

The spill was discovered on Sept. 29 and was quickly contained. According to Kris Roberts, leader of the environmental response team with the state Department of Health, there was no risk to groundwater in the area as a result of the oil spill and, as there are no bodies of surface water within a five-mile radius of the leak site, surface water is not under threat either.

The duration of the spill and its cause are still under investigation, Reuters said. The Texas-based company explained that the section of the pipeline where the spill occurred is shut and will remain so until it has been repaired. Tesoro Logistics stated that containing the spill, the repair work and the remediation efforts will cost up to $4 million.

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The spill occurred at a segment located about nine miles north-east of the city of Tioga. The pipeline run by Tesoro Logistics carries crude oil from the Bakken shale and this leak is the largest since the beginning of the shale energy boom at the Bakken shale formation area, the news source said.

North Dakota is the second largest oil producer in the country, with an average output of 874,000 barrels per day recorded in July.