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.
"There was really no flowing water in the tributary," Suess said. "But there were pools of standing water all through it."
Suess said the tributary goes through a culvert under a road. He said the culvert was blocked off to stop potential flow, and the company began building earthen dams across the tributary.
"This is preventative action, in case we got heavy rain, which actually is in the forecast, which could get the creek flowing again," Suess said.
Polar Midstream will now be digging up the pipeline to fix the leak. Suess said after that, the company will pump the brine water out of the creek, and the sediments will be evaluated, to see what more will need to be done.
"It could have impacted the Missouri River or Lake Sakakawea," Suess said. "Field testing, though, does not indicate that it has been impacted."
Suess said some plant life may be affected in the spill site. But because the water wasn’t flowing, he doubts any fish were harmed. He said DEQ inspectors are on site.