Cause of oilfield wastewater spills in North Dakota unknown

BISMARCK, N.D. (AP) — North Dakota health officials do not yet know what caused a pair of pipeline spills last week that leaked oilfield wastewater into a tributary of the Missouri River and over some pastureland.

State Health Department environmental scientist Bill Suess said cleanup was ongoing Tuesday at the two sites where produced water — a byproduct of oil production that contains saltwater and oil, and sometimes chemicals from hydraulic fracturing operations — leaked.

"We still don't know what happened," Suess said.

Polar Midstream LLC reported July 14 that 21,000 gallons (79,500 liters) of oilfield wastewater leaked from an underground pipeline and into an unnamed tributary of the Missouri River. Suess said investigators don't think the spill reached the river, based on samples that were collected. The produced water in the tributary was being pumped out and "flushed" with fresh water, he said.

The second spill leaked more than 12,000 gallons (45,425 liters) of oilfield wastewater, impacting an unknown amount of pastureland near Epping.

Both spills were reported by Polar Midstream, a unit of Woodlands, Texas-based Summit Midstream Partners LLC, which was responsible for a 3 million-gallon (11.4 million liter) produced water leak from a pipeline in 2014, the largest of its kind in the state.

Summit and its subsidiaries installed spill detection equipment on all of its pipelines following the 2014 spill that leaked for months and contaminated Blacktail Creek. The wastewater also flowed into the Little Muddy and Missouri rivers. State officials said there was no harm to drinking water supplies at the time because it was so diluted.

Zak Covar, company vice president, said the detection equipment helped find the leaks quickly, thought their cause were still a mystery.

"We are focused on remediation," Covar said.