The team of UM researchers focused on the layer of lead scale inside ten service line samples from around Flint. Service lines connect homes and businesses to city water mains. In addition to examining pipe samples under a scanning electron microscope, the researchers pulverized the pipe linings to analyze what they're made of.
In the Flint pipes, they found a greater ratio of aluminum and magnesium to lead than is typical for lead service lines, when compared with data from 26 other water utilities.
Study co-author Brian Ellis is an assistant professor of civil and environmental engineering at the university.
He says the layer of rust that naturally develops in water pipes developed a “Swiss cheese” pattern.
“It demonstrated to be depleted with respect to lead, and we attributed this to the change in water chemistry,” said Ellis.
The UM researchers estimate that the average lead service line released 18 grams of lead during the 17 months that Flint’s tap water was without proper corrosion controls.
"If we average that release over the entire period the city received Flint River water, it would suggest that, on average, the lead concentration would be at least twice the EPA action level of 15 parts per billion," said Terese Olson, an associate professor of civil and environmental engineering and lead author of a study.
The researchers are now doing some house hunting in Flint. They are looking for a home with a lead service line where the water service has been cut off since 2014. The researchers want to use the home to verify their prediction of the amount of lead released by analyzing a lead service line that was not exposed to the corrosive Flint water.
The study is published in the journal Environmental Science and Technology Letters.