The Canadian company working to clean up the spill has also closed a third pipeline after a possible leak was found in upstate New York.
Enbridge, the owner of the pipeline that broke in Romeoville, has had two significant pipeline breaks in seven weeks. A third, smaller oil line was shut down in New York Monday, though that does not appear to be from a significant leak.
Still, this raises questions about maintenance practices on oil pipelines that have some years on them, and at the same time it may also reveal that even "better than required" maintenance doesn't always prevent problems.
The 12-foot section of Enbridge Romeoville pipeline that contained the break-point is on its way to Washington for analysis. A new section is being welded into place. That doesn't mean oil starts flowing again right away. There must still be regulatory approval. And it is unclear how long that may take.
While that process goes on, investigators will try to determine what caused a 2-inch crack in the bottom of the steel tube.
Professor Sheldon Mostovoy of the Illinois Institute of Technology said shifting soils can cause problems.
"It can put stresses on the pipe. If there's water nearby, the water normally congregates underneath the pipe, and if the water is highly acidic, for example, that can work it way into the pipe as a general corrosion or stress corrosion," said Mostovoy.
Mostovoy is an IIT expert on material and metallurgy. He is not a party to the investigation and spoke to ABC 7 Tuesday in general terms about pipeline stresses. But his point about the possibility of water playing a role is interesting, because at the site of the oil pipeline break in Romeoville, investigators also found a fractured water service line leading to a nearby business.
It is too early to say if there is a link, but it is something investigators will be looking into.
Pipeline owner Enbridge says it inspects this line at two-year intervals. That exceeds government requirements. The last inspection was in 2008.
Pipeline owners typically used a device called a "smart pig," which is run through the line and uses ultrasound signals to determine whether the pipe is showing signs of weakness or deterioration.
"So if there's any corrosion that goes on within the pipe, or outside the pipe more likely, it can more likely detect that in the signal coming back from the ultrasound," said Mostovoy.
Stress corrosion caused by something outside the pipe is not something easily detected by a computerized machine running inside the pipeline. Some of this may be touched on when a House subcommittee holds a hearing on the Enbridge oil line break in Michigan in late July. That line was quickly repaired, but it is still not yet operational. Enbridge estimates the cost of cleanup there at between $300 and $400 million.