State regulators say human error caused a pipeline spill that leaked more than 11,000 gallons (42,000 liters) of oilfield wastewater in western North Dakota.

The Bismarck Tribune reports that the spill in Dunn County on Sunday was reported by Crestwood Midstream.

Department of Mineral Resources spokeswoman Alison Ritter says crews forgot to close a valve on the pipeline, which caused the produced water spill.

Produced water is a mixture of saltwater and oil that can contain drilling chemicals.

Regulators say the spill was contained within a pipeline trench and most of it had been recovered by Monday.