Over 176,000 gallons of oil leaked from a Belle Fourche Pipeline Co. pipeline last week, with 130,200 gallons spilling into a tributary of the Little Missouri River and another 46,200 gallons flowing into a hillside, officials said Monday.
The spill discovered by a landowner Dec. 5 did not end up detected by monitoring equipment on the pipeline, which is owned by of True Companies of Wyoming.
The spill has contaminated 5.4 miles of Ash Coulee Creek but does not appear to have reached the Little Missouri River, said Bill Suess, spill investigation program manager for the North Dakota Department of Health.
The spill estimate of 4,200 barrels, or 176,400 gallons, is a “rough estimate” provided by the company, Suess said. Cleanup crews had recovered 878 barrels, or 36,876 gallons, of oil as of Sunday night.
At least two cows have been confirmed dead in the area of the oil spill, but the cause of death has not been verified by a veterinarian, Suess said. Crews assisted the landowner in moving cattle away from the creek and have trucked in water, he said.
It’s unknown how long the pipeline, built in the 1980s, had been leaking before the landowner discovered it.
The pipeline had pressure gauges and meters to monitor for leaks, said Kevin Connors, pipelines program supervisor for the North Dakota Oil and Gas Division.
The company also does aerial inspections of the pipeline about twice a month, Connors said.
Why the monitoring equipment didn’t detect the leak is part of an ongoing investigation, said True Companies spokeswoman Wendy Owen. The pipeline does not have a constant flow, which may have masked the leak from being detected, she said.
The 6-inch pipeline, which transports an average of 1,000 barrels of oil per day though rugged Badlands terrain, is buried in a hill that is slumping, Suess said. Crews have been unable to investigate further because the hillside is unstable, he said.
“Whether the slumping contributed to the break or the break contributed to the slumping, we don’t know yet,” Suess said.
The pipeline shut down after officials discovered the spill and they capped it at the spill location.
The company is working with SWAT Consulting, a spill response company based in Alberta, Suess said. An additional 60 workers should come in this week to assist.
“The weather continues to still be the issue because the safety and security of the responders is our No. 1 priority,” Owen said.
The spill affected privately owned land as well as U.S. Forest Service land, Owen said.
“It’s very, very remote,” Owen said. “The terrain, the topography itself does make access points difficult.”