The North Dakota Department of Environmental Quality says approximately 500 barrels of produced water leaked from a pipeline east of Williston last week.
The pipeline is owned and operated by Polar Midstream.
Spill investigation program manager Bill Suess said it’s mostly salt brine, with a small bit of oil in it. He said the company's metering indicated a loss of pressure on the pipeline – and company inspectors found the leak about 20 miles east of Williston.
Suess said the water flowed down a hill into a small tributary of the Missouri River.