John Badman|The Telegraph Scores of workers were on the site of the pipeline leak last month near the intersection of Illinois 143 and 159 in Edwardsville. Officials have blamed a failed weld for the oil spill.

EDWARDSVILLE — A failed weld on the Woodpat Pipeline is being blamed for at least 3,900 barrels of crude oil leaking into the Cahokia Diversion Channel.

The failure was cited in the preliminary report released Tuesday from Marathon Pipe Line LLC and the National Transportation Safety Board (NTSB) about the March 11 spill near the intersection of Illinois 143 and Illinois 159. 

According to officials, the 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. A batch is one type of liquid product that is being transported in a pipeline capable of transporting different types of liquid products.

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

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 report states. The pipeline was most recently hydrostatically tested in 2018.

Around 8:15 a.m. on March 11, a rupture occurred in a girth weld, a type of arc welding used in the joining of two pipes along the circumference of the pipeline during construction. 

​​The report states that, while on scene, NTSB investigators observed complete circumferential separation at the weld at the rupture origin. Per the report, the investigators retained both sides of the fractured girth weld and an adjacent girth weld as evidence for laboratory testing.

The released crude oil emerged into Cahokia Channel from the bank adjacent to the pipeline; about seven miles of the channel were impacted by the oil spill. The furthest location downstream where crude oil was recovered was a containment boom site about 2.5 miles from the Mississippi River, according to the report.

No injuries occurred and the spilled crude oil did not ignite. ​

Following the rupture, Marathon and its contracted oil spill response organizations deployed containment booms, vacuum trucks and personnel at 10 locations along the creek. Repairs to the pipeline have been completed and federal regulatory authorities have authorized the restart of the pipeline. 

The Woodpat Pipeline is a 22-inch line that runs about 75 miles, between Wood River and Patoka. For part of its length the pipeline parallels the Cahokia Diversion Channel which leads to the Mississippi River. Cahokia Creek is a separate body of water that flows into the diversion channel further downstream.

The Woodpat Pipeline was constructed in 1949 and purchased by Marathon Pipe Line, LLC, in 1968.

The NTSB 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 included Marathon, the Environmental Protection Agency and the Pipeline and Hazardous Materials Safety Administration.