Road Salt Is Washing Into The Mississippi River… And It’s Not Washing Out

7:45 minutes

A truck carries salt mined from an enormous salt deposit behind it.
A loader carries a load of salt to a waiting truck Dec. 13, 2022 on Jones Island in Milwaukee, Wisconsin. Credit: Mark Hoffman, Milwaukee Journal Sentinel

state of science icon

This article is part of The State of Science, a series featuring science stories from public radio stations across the United States. This story, by Madeline Heim, was originally published by the Milwaukee Journal Sentinel.

This winter has already brought significant snowfall to much of the U.S. Historically, more snow has meant more road salt. It’s an effective way to clear roads — but also brings cascading environmental impacts as it washes into rivers and streams.

But amid one powerful winter storm that walloped the Midwest in December, employees from the La Crosse County Facilities Department did something a little different.

As usual, they clocked into work well before dawn to plow the county’s downtown parking lots. They were followed by facilities director Ryan Westphal, who walked each of the lots, checking for slick spots. Finding none, he didn’t lay any salt down on top.

That’s a major departure from how he would have handled the situation a few years ago – before their department made the decision to dramatically cut back on salt use to prevent it from flowing into waters like the nearby Mississippi River, which new data show has been growing saltier for decades.

Under the previous protocol, in Westphal’s words, his crew would have “salted the crap” out of the lots after a snowfall like this, without giving deference to whether they actually needed it. Today, there’s a careful calculation after each time it snows to ensure they’re using just the right amount of salt.

Westphal acknowledged that the new way isn’t faster, nor is it easier. If a half-inch of snow falls today, for example, a handful of employees will take a few hours to plow the lots, versus the one employee who could have thrown salt down in an hour.

But he said the extra time is worth it.

“There’s pretty good evidence that if we continue to use salt at the rate we do now, it’s going to be detrimental to the rivers and lakes eventually,” Westphal said. “We need to do something about it now.”

The use of road salt during winter is nothing new for people across the Midwest, particularly in its upper stretches where the presence of snow and ice can linger from December into April. But there’s growing awareness of the harm it can cause to freshwater resources – wreaking havoc on aquatic life, disrupting ecosystems, making its way into groundwater and corroding pipes.

New data reveal that levels of chloride – one of the elements that make up salt – have increased by more than a third since the late 1980s across the entire Upper Mississippi River basin, which extends from the river’s headwaters in Minnesota to southern Illinois. Reported increases are even higher at monitoring sites in Wisconsin and Minnesota. And the problem is magnified in smaller rivers and streams that can’t flush the same volume as the Mississippi.

There are other reasons for increased chloride in water, like salt from water softeners and the use of potassium chloride fertilizer, but road salt is typically a dominant source in colder states.

It’s leading people like Westphal – as well as those in state and federal environmental agencies – to realize a change is needed.

The River is Getting Saltier

Unlike other pollutants, chloride doesn’t break down in water over time. In other words, once it’s in, there’s no getting it out. Just a teaspoon of salt can pollute five gallons of water forever.

So the increase in chloride in the river isn’t from a recent overabundance of road salt being laid down in the winter months. It has built up over decades. And because it doesn’t break down, it’s all headed down into the Gulf of Mexico.

In a forthcoming report on water quality in the upper river, the Upper Mississippi River Basin Association (UMRBA) found that chloride had increased at least 35% across the basin between 1989 and 2018. All 14 sites on the river where chloride was measured, plus one on the Illinois River, which feeds to the Mississippi, showed increases in the pollutant during that time period, according to UMRBA data.

At a Wisconsin Department of Natural Resources monitoring site in Lynxville, about an hour south of La Crosse, chloride levels in the river had increased by more than 60% since the 1980s, according to a 2021 study from two Mississippi River water quality specialists with the DNR.

And chloride levels in the portion of the river that runs through the Twin Cities metro area increased 81% between 1985 and 2014, according to a 2016 report from the nonprofit group Friends of the Mississippi River.

Chloride levels are rising at all 43 DNR river monitoring sites across Wisconsin.

“It really shows that we’re not on a sustainable path,” said Shawn Giblin, who coauthored the 2021 DNR study. “You can’t keep having 1 to 4% annual increases. You’re eventually going to get to chronic toxicity levels.”

The concept of freshwater becoming saltier, known as freshwater salinization syndrome, isn’t unique to the upper Midwest. In November, the U.S. Environmental Protection Agency said its scientists have been studying the issue because of “dramatic” salt concentration increases in freshwater around the country and globally.

Both the EPA and state environmental agencies set limits for when chloride becomes toxic to aquatic life. In Wisconsin, for example, 395 milligrams per liter of chloride in a water body for days at a time is considered chronically impaired, while 757 milligrams per liter, which is instantly toxic to fish, is considered acutely impaired.

Though the Mississippi River is under the limit, many smaller tributaries are not. In Minnesota, 50 lakes and streams are considered impaired by chloride, and another 75 have chloride levels near the standard, according to the state’s pollution control agency. In Wisconsin, 51 rivers and one lake are chronically impaired by chloride, DNR data show – most in the southeast part of the state.

Ecosystems Hurt by High Chloride

High chloride levels can have far-reaching destructive impacts on ecosystems.

Salt increases the electric current in a body of water and makes the overall environment less habitable, said Lauren Salvato, who coordinates the water quality program for the Upper Mississippi River Basin Association. By adding more and more to the water, the ecosystem starts acting more like an estuary, an area where a freshwater river or stream meets the ocean.

Toxic amounts of chloride can kill freshwater aquatic plants and animals. That includes zooplankton, microscopic animals that feed on algae. Die-offs can then lead to harmful algal blooms, which have their own adverse effects.

Chloride can also make its way into groundwater, the source of  drinking water for about two-thirds of Wisconsinites and about three-fourths of Minnesotans. Salt’s other component – sodium – can alter the taste of water and could pose health risks for people who are on low-salt diets.

Finally, elevated chloride levels can also pose an infrastructure problem, corroding lead and copper drinking water lines and leading to contamination.

Searching for Solutions

Many municipalities are already experimenting with ways to fix the problem. Brining, where salt is mixed with water before being applied to roads, resulted in a 23% reduction in salt use on average on Wisconsin highways, a 2022 study from the University of Wisconsin-Madison found. Some places even use beet juice to help the solution work at a lower temperature, since standard road salt is much less effective at temperatures lower than 15 degrees.

That can be combined with other techniques, like pre-wetting salt so it doesn’t bounce off roads and using underbody plows, which can remove hard-packed snow better than plows with a front blade.

In Minnesota, the state pollution control agency leads a Smart Salting training program to help road salt applicators better understand how too much salt can affect the environment. The training aims to help applicators identify the best balance between ensuring safe traveling conditions and protecting the environment.

To date, about 5,300 people are currently certified under the program, said Brooke Asleson, the state’s chloride reduction program coordinator.

The idea emerged in 2005, sparked by concern about Shingle Creek, which joins the Mississippi River in Minneapolis and was the first water body in the state to be designated as chloride-impaired about a decade prior.

Two years ago, the state made it a requirement for any entity that receives a municipal stormwater permit to get trained on proper salt use and the importance of protecting water quality. Enrollment in the Smart Salting training has significantly increased since then, Asleson said.

Some participants simply weren’t aware that they could be using less salt, she said. After implementing techniques from the training, many are able to cut their salt use in half.

One other change that could make a difference: protecting people from slip-and-fall lawsuits as long as they follow proper salting guidelines.

“Ultimately, the fear (from applicators) is if they don’t put enough road salt down, someone’s going to slip and sue them,” said UMRBA’s Salvato.

New Hampshire legislators passed a law in 2013 that gave partial immunity from lawsuits to snow-removal companies that participated in a voluntary training program for applying road salt. Similar bills have been floated in Minnesota – where it’s been proposed but not yet passed – and Wisconsin, where one is currently being drafted.

Communicating Why It Matters

Advocates for reducing road salt say public awareness is critical.

The general public is “mostly unaware” of trends in chloride contamination and the harmful effect it can have on the environment, according to a chloride resolution UMRBA adopted in February 2022. The resolution aims to facilitate upper basin states working together to reduce chloride in the river.

The EPA has also convened a group of cold-weather states to help them share information about easing the impacts of winter road maintenance on the environment.

“It is a big lift to tackle this chloride issue,” Asleson said. “The more collaboration we can do as states to share information and knowledge with each other, the better off all of us will be at protecting our environment.”

For Westphal, in La Crosse County, it wasn’t hard to convince his staff to get on board with being more mindful of their salt use because many of them share his appreciation for the Mississippi River and nearby lakes. His passion for the issue comes from a longtime friendship with Giblin, the Wisconsin DNR water quality specialist.

But this winter, which has already been a snowy one, could be a big test.

To get more salt applicators on board, Westphal sees three things that need to happen: Grant money for brining equipment and other materials, protection from lawsuits, and finally, some pressure from the state to heavily encourage people to make the switch.

Westphal said it comes down to “selling people on the right thing versus the easy thing.”

The Mississippi River, running just blocks away from their downtown campus, serves as a powerful reminder of why he thinks it’s right.

This story is a product of the Mississippi River Basin Ag & Water Desk, an editorially independent reporting network based at the University of Missouri School of Journalism in partnership with Report For America and the Society of Environmental Journalists, funded by the Walton Family Foundation. 

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Segment Guests

Madeline Heim

Madeline Heim is an environment reporter for the Milwaukee Journal Sentinel and the Mississippi River Basin Ag and Water Desk.

Segment Transcript

MADDIE SOFIA: This is Science Friday. I’m Maddie Sofia.

KATHLEEN DAVIS: And I’m Kathleen Davis, and now, it’s time to check in on the state of science.


SPEAKER 1: This is KER–


SPEAKER 3: Saint Louis Public Radio.

SPEAKER 4: Iowa Public Radio news.

KATHLEEN DAVIS: Local science stories of national significance. In many parts of the country, we are already in peak snow season, and to combat snowy and icy roads, there’s one thing that usually works pretty well. And that’s road salt. Salt is good at preventing your car from sliding all over the road.

But when too much salt runs into waterways, it can disrupt sensitive river ecosystems. It can also corrode water pipes and make drinking water too salty. Our next guest looked into this growing problem in Wisconsin and across the upper Mississippi River basin. Madeline Heim is an environment reporter for the Milwaukee Journal Sentinel and the journalism collaborative The Mississippi River Basin Ag and Water Desk. Madeline, welcome to Science Friday.

MADELINE HEIM: Thanks so much for having me.

KATHLEEN DAVIS: Nice to have you. So to start off, Madeline, can you explain how we got here. It’s not just that we’ve been eagerly over salting the roads in the past couple of years, I would imagine.

MADELINE HEIM: Right, so chloride, which is what we’ve been finding in elevated levels across the Mississippi River and, frankly, in lots of waterways across the upper Midwest, it’s a pollutant that doesn’t dissolve or break down over time. So essentially, once you are putting in road salt, putting in chloride into a waterway, if you start putting that in 1980, that stuff is still in there today.

The Mississippi River basin, upper basin overall, has seen at least a 35% increase in chloride levels since the late 1980s. Because it never goes away, obviously, it’s going to be in there for life.

KATHLEEN DAVIS: Just how high are these chloride levels in the upper Mississippi River basin and in Wisconsin? How grim is the situation?

MADELINE HEIM: Yeah so it’s a little bit different, depending on where you look. The upper Mississippi River and the river, in general, is, obviously, a huge body of water, so it does have a lot of capacity to flush, flush the water in and out. And so although we’re seeing large percentage increases of chloride– for example, there’s a spot a monitoring station in Western Wisconsin that was saw like a 66% increase from the 1980s to today– but the numbers aren’t as huge because the river has the capacity to flush that stuff out.

The places where it’s more difficult are the smaller streams, and rivers, and lakes, and some of those places have reached acute toxicity for chloride. That’s something that both the EPA and several individual states measure. And so we’ve seen places in the Twin Cities or in southeastern Wisconsin– obviously, that’s not along the river basin, but there are some places that have reached acute toxicity for chloride.

So it’s kind of a mixed bag. There are some water bodies that have not reached that point, but I think folks who are interested in this and concerned about it are worried that they’re going to eventually.

KATHLEEN DAVIS: So what happens when a waterway reaches that acute toxicity? Why is it so dangerous?

MADELINE HEIM: Yeah so essentially, if you think about the aquatic life, and the fish, and the plants, and the birds, and everything that lives in a freshwater ecosystem, they, obviously, live in a freshwater ecosystem for a reason. They’re adapted to living in freshwater. And so when the water becomes saltier and, in some of these cases, becomes excessively saltier, they just can’t handle that.

So those toxicity levels that I mentioned before from the EPA, if you’re reaching these acute levels, which, obviously, that does take a lot of chloride– but this has happened in some places– that can kill plants and animals pretty quickly. It’s changing their whole entire habitat, which they’re used to freshwater, to something that looks more like saltwater, obviously, not as salty as an ocean or anything. But it’s just changing gradually, and that can have an effect there.

And as far as further-reaching effects, salt, when it gets into groundwater, it gets into pipes. It’s corrosive, so it can corrode infrastructure, lead and copper pipes. And if it gets into drinking water, drinking water that’s too salty, we can actually start to taste that. Obviously, no one wants their drinking water to taste super salty, but for folks who are on like low-sodium diets, for example, that tends start to be unhealthy.

KATHLEEN DAVIS: Yeah, I would imagine so your reporting did focus on the upper Midwest, but I would imagine that this isn’t just a problem there. Is that right?

MADELINE HEIM: Yeah, this is a pretty widespread problem, so much so that the EPA had released a statement, believe, late last year, just saying that they’re looking at this issue of freshwater salinization, that it’s a big enough issue that they’re looking at it countrywide, that fresh water is turning into turning into salt water, so to speak.

And I would say it’s prevalent here in the upper Midwest with road salt just because we are a colder climate and we have to use that. But there are other reasons that chloride can get into the water through water softeners or potassium chloride fertilizer, so there’s certainly this issue in other places. With colder states, it does tend to be road salt that’s a dominant factor.

KATHLEEN DAVIS: In your reporting you also looked at some solutions to this problem. Can you tell me about some of those?

MADELINE HEIM: The biggest thing that I heard from the experts that I talked to and the folks just working on the ground on this stuff is that it’s really about– not about cutting salt use out entirely because, obviously, some salt use is really important for keeping us safe and keeping us from slipping and falling. And so no one’s arguing we should just completely stop using salt.

It’s more about using it properly and applying it properly, so for example, salt doesn’t work very effectively at temperatures below 15 degrees. So if it’s 0 degrees out and you’ve got your salt trucks out there just dumping salt pile after salt pile on the road, that’s not actually really going to do anything. So a lot of the people who are working on this are interested in helping salt applicators really understand and become educated about the proper salt application, how much to apply.

And then we do also see solutions like brining, which is when you mix salt with water, dissolve the salt a little, cut down on how much salt you’re using. In Wisconsin, it cut down on salt almost a quarter on average on Wisconsin highways last year. So it works, so there’s certainly like solutions to be found there.

Of course, any new equipment that people are going to have to buy is expensive, so I think the facilities folks who are applying salt are certainly looking to– they’re going to look for needing grants and things attached to that. But there’s definitely lots of possible solutions out there.

KATHLEEN DAVIS: And some cities are using beet juice, too, right?

MADELINE HEIM: Yeah, yeah, beet juice is a– you can use that as a brining agent to help it work in lower temperatures as well. So yeah, that’s certainly one of the more creative solutions out there.

KATHLEEN DAVIS: Well, as long as nobody is licking the roads, hopefully, that solution will be a good one. Thank you so much, Madeline, for joining us.

MADELINE HEIM: Thank you so much for having me.

KATHLEEN DAVIS: Madeline Heim, environment reporter for the Milwaukee Journal Sentinel and the journalism collaborative The Mississippi River Basin Ag and Water Desk.

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