GRAND FORKS — A fatigue crack likely the result of a defective pipe was the cause of a major crude oil spill in Walsh County in 2019, according to an investigation report newly released by the U.S. Pipeline and Hazardous Materials Safety Administration.

Many details about the cause of the Oct. 29, 2019, Keystone Pipeline rupture remain unknown to the public, as the 183-page report is heavily redacted. TC Energy, the Canadian former operator of the pipeline, redacted the report to protect trade secrets and information that could reasonably endanger an individual, in accordance with federal open records law, according to PHSMA.

However, the document concludes that part of the root issue could be "ineffective quality control" and inadequate inspections at the Berg Steel Mill in Panama City, Florida, where the damaged portion of pipeline was produced.

The report also rules out a slate of possible causes, including that damage was done intentionally to the pipeline.

The spill released about 383,000 gallons of crude oil onto about 5 acres of wetlands outside Edinburg, North Dakota, and is among the largest crude oil spills in the state's history. Remediation of the affected land was completed in spring 2020. At that time, North Dakota Department of Environmental Quality Director Dave Glatt praised the company's cleanup efforts as some of the best and smoothest his agency had seen.

TC Energy eventually reached a settlement with the NDDEQ and agreed to pay a roughly $52,000 fine.

The investigation report — formally the Root Cause Failure Analysis — was authored by RSI Pipeline Solutions, a consulting firm based in Ohio. It is dated April 1, 2020.

According to the report, just before 9 p.m. Oct. 29, 2019, a leak detection alarm went off, the Edinburg and Niagra pump stations tripped, and a controller — an employee who monitors the pipeline systems — stopped the pumps. Rural pump stations in the region frequently experience unexpected shutdowns, sometimes as often as multiple times a week, and because of this, there was possibly a slight delay in corrective action. However, within 5 seconds, the controller realized something more serious was wrong and moved to shut down the system, the report said.

The report found that the leak detection system, control room response and emergency response all adequately reacted to the release. It did note that there is opportunity for additional controller training. It also suggested pipeline operators should work with rural utility providers to improve reliability of services to pump stations.

Last year, TC Energy spun off its oil pipeline business into a new company called South Bow Energy. The pipeline remains active under the new operators.

Editor's note: This story has been updated to more accurately reflect the name and operation status of the Keystone Pipeline.