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WUWM's Susan Bence reports on Wisconsin environmental issues.

UW-Milwaukee researcher looks into how road salt impacts Wisconsin waterways

Snowplow spreading salt on the highway
nd700
/
Adobe Stock
Milwaukee has been busy salting roadways.

Milwaukee has been busy salting roadways due to this week’s icy conditions, but that salt doesn’t just stay on the road. Instead, it can make its way into waterways and groundwater, impacting water quality and animals.

UW-Milwaukee assistant professor Charlie Paradis is studying how that road salt impacts waterways in our area. “We suspect that there’s a subsurface component that is storing road salt over the summer months,” he explains.

Paradis says that the Southeast Wisconsin Regional Planning Commission came up with the hypothesis. “SEWRPC wrote a really nice report two or three years ago about high chloride concentrations in many rivers throughout southeastern Wisconsin. They actually hypothesized in the summer when there is no road salt applied that road salt is actually being stored in groundwater — that is in hydraulic connection to surface water — and that [it] is persistent chloride throughout the summer months. But that hypothesis was never really tested."

UWM grad student Leah Dechant filtering samples along the Root River in Racine.
Charlie Paradis
UWM grad student Leah Dechant filtering samples along the Root River in Racine.

Paradis’ labis putting the hypothesis to the test in a river with chronically high chloride levels. “Every week or so in the summer, [students] drive down to Racine and sample two sites on the Root River, a rural site and an urban site, for groundwater and river water and precipitation,” he explains.

They tease out the river’s signals, he adds. “The signals are flow, how fast is the river flowing, chloride concentrations. Rain [and] precipitation is another signal, and isotopic signatures that can tell you about the age of the water. So, if I’m in the river and I’m taking a sample, maybe I can look at that water and look at its isotopic composition and tell you whether most of its young from rain or old from groundwater."

UWM student Adam Schmidt running samples in Paradis lab for water quality.
Charlie Paradis
UWM student Adam Schmidt running samples in Paradis' lab for water quality.

The samples are tested in Paradis’ lab, “and then we send them to Tim Wahl at the School of Freshwater Sciences and he does [a] really high level analysis of these stable isotopes,” he says.

All of that data determines where the chloride is coming from and whether it’s old or young. “We think it’s coming from the groundwater and that it’s old, but we have to have enough of a data set to test that hypothesis,” Paradis explains.

Paradis says public education is also a component of the project. He’s got two models — one the size of a bathtub, which helps illustrate how road salt and other inputs influence watershed. “So the idea is to get these two models going, bring them down to Discovery World or the Betty Brinn Children’s Museum or the Urban Ecology Center. We identified three places that we can take these physical models to teach people about groundwater flow and salt water transport."

Hydrogeologist Charlie Paradis uses sampling, testing, modeling & physical models like the one behind him to learn and teach more about the impacts of road salt on our waters.
Susan Bence
/
WUWM
Hydrogeologist Charlie Paradis uses sampling, testing, modeling & physical models like the one behind him to learn and teach more about the impacts of road salt on our waters.

And, Paradis thinks the project could help inform policy. “Road salt is good for public safety, but it can be hurting the environment. So where’s that sweet spot at? Well the best way to determine where the sweet spot is is to have all the information you possibly could have. [But] we are lacking scientific information on road salt transport in the summer month."

Graduate student Leah Dechant works with Paradis. She'll be presenting preliminary findings at the Wisconsin section of the American Water Resources Association Annual Meeting in March.

Paradis says the final findings will be presented at next year's meeting. In the meantime, his team will likely take its groundwater models on the road starting this summer.

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Susan is WUWM's environmental reporter.
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