Containment booms on Cahokia Creek.

​Containment booms on Cahokia Creek.​

Marathon Pipe Line LLC Hazardous Liquids Pipeline Release

Investigation Details

What Happened

 This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed.

On March 11, 2022, at about 8:15 a.m. local time, Woodpat pipeline, a 22-inch-diameter hazardous liquids pipeline operated by Marathon Pipe Line LLC (Marathon), ruptured in Edwardsville, Illinois. The rupture resulted in the release of about 3,900 barrels of crude oil, some of which entered Cahokia Creek, a tributary of the Mississippi River. No injuries occurred, and the crude oil did not ignite. 

​​Preliminary information indicates shortly after the rupture, Marathon’s pipeline operations center staff were alerted to a rapid drop in pipeline pressure by a rate-of-change alarm from a supervisory control and data acquisition system. [1] The control center closed valves at the two nearest pump stations remotely, isolating the ruptured pipeline.

​The released crude oil emerged into Cahokia Creek from the bank adjacent to the Woodpat pipeline, and about 7 miles of Cahokia Creek were impacted by the oil spill. The furthest location downstream where crude oil was recovered was a containment booming site about 2.5 miles from the Mississippi River.

Following the rupture, Marathon and its contracted oil spill response organizations deployed containment booms, vacuum trucks, and personnel at 10 locations along the creek. Remediation and clean-up work is ongoing.

​The Woodpat pipeline was constructed in 1949 and purchased by Marathon in 1968. The pipeline pressure immediately before the rupture was about 479 pounds per square inch, gauge, which was under the maximum operating pressure of 881 pounds per square inch, gauge. At the time of the incident, a routine batch movement of heavy, sour crude oil was underway. [2] The batch movement was progressing as expected before the rupture, and no evidence was found to indicate any outside parties were near the rupture site at the time of the accident.

Previous in-line inspections and field studies performed for Marathon by various contractors had identified movement of the pipeline, erosion, and soil subsidence in the area near the rupture site. The pipeline was most recently hydrostatically tested in 2018.

​​While on scene, National Transportation Safety Board (NTSB) investigators observed complete circumferential separation at a girth weld at the rupture origin. [3]  NTSB retained both sides of the fractured girth weld and an adjacent girth weld as evidence for laboratory testing.

NTSB’s investigation is ongoing. Future investigative activity will focus on geohazard management, metallurgy, comparing the forces exerted on the pipeline to its ability to withstand strain, and the ongoing environmental response.

Parties to the NTSB investigation include the Environmental Protection Agency, the Pipeline and Hazardous Materials Safety Administration, and Marathon.


[1] A rate-of-change alarm is triggered when a reading changes by a prescribed amount in a certain time frame.
[2] Batch refers to one type of liquid product that is being transported in a pipeline capable of transporting different types of liquid products.
[3] A girth weld is a weld that runs circumferentially around the pipeline and is typically completed when the pipe is constructed. 

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