Other partners in the invesigation are the federal Department of Transportation's Pipeline and Hazardous Materials Safety Administration and the pipeline operator, Enbridge Energy.
These government agencies will start off their investigation by recreating the scene digitally and mapping it out with a GPS software. The maps will tell them where the pipelines are, including the location of the fittings, the width of the trench, and more.
Darren Lemmerman is the acting chief engineer at the Minnesota Office of Pipeline Safety. He says Enbridge, the pipeline operator, will also submit information about its operating pressures -- details like when the company starts and shuts down the pipelines.
"There will be a review of their maintenance procedures. After that, the pipeline itself will be removed -- the components that failed -- and sent out for testing," says Lemmerman.
After that information is compiled, Enbridge will submit a report to the investigating government agencies. Lemmerman says the timing of the process will vary depending on what they find, what will be missing, or what steps may have to be redone.
About two weeks ago, Enbridge started repairing the pipeline that leaked Wednesday evening. The part that needed repair was taken out for testing.
"When they put in the new part, about two-thirds of the way through the maintenance process of putting in the new part, something failed," sayd Lemmerman.
And that's what's under investigation at this time to determine the cause.
Investigators will also interview workers who were on site when the explosion and fire took place. They'll ask questions about what workers were doing before the explosion, what they saw, heard, and smelled.
Once the report is completed, the National Transportation Safety Board and the federal Office of Pipeline Safety will each review it. They'll identify any deficiencies and ask Enbridge to make corrections so that an incident like this doesn't happen again.
Lemmerman says because the fire burned for such a long period of time, a lot of the evidence is gone. And that's the biggest challenge they have to deal with.
"When evidence is damaged, altered, or destroyed due to a fire, we take past history from other incidences and other engineering standards and practices to determine what may have happened. In some instances we will never know exactly," he said
Enbridge contractors and consultants are also working to gather information about the environmental impacts of the explosion. This separate investigation involving environmental consequences and cleanup will be monitored by the Minnesota Pollution Control Agency.