Road salt is washing into Wisconsin's major waterways, with alarming results

Madeline Heim Caitlin Looby
Milwaukee Journal Sentinel

As temperatures plummet, snow and ice will take up take their place in Wisconsinites’ lives – and so, too, will road salt. 

That's nothing new.

But there is growing awareness and concern that salt is making its way into the state’s rivers and lakes, with the potential for catastrophic consequences.

It can wreak havoc on aquatic life, disrupt the ecosystem of a body of water, make its way into groundwater and corrode pipes.  

New data reveals how serious the problem is getting. At a long-term monitoring site on the Mississippi River south of La Crosse, levels of chloride – one of the components of salt – have increased 66% since the early 1980s. 

A loader carries salt to a waiting truck Tuesday on Jones Island in Milwaukee. In an internal report, DNR staff members wrote this year that Wisconsin is on an “unsustainable” path of road salt usage.

And roughly 2.2 billion pounds of chloride flushes into Lake Michigan each year, according to a recent study. That’s the equivalent weight of 9,500 blue whales. 

The problem is magnified in smaller tributaries, putting them at a greater risk because they don’t have as much water to dilute the salty pollutant.  

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.

In an internal report to a committee of Wisconsin’s Department of Natural Resources that works on water quality issues, DNR staff wrote this year that the state is on an “unsustainable” path of road salt usage.

And this isn’t a seasonal problem. Chloride, unlike other pollutants, doesn’t break down over time. In other words, once it’s in, there’s no getting it out. 

“All we can do at this point is slow the increase,” said Shannon Haydin, the DNR’s stormwater section manager, who helped write the chloride report. “We’re going to potentially see some significant concerns in our water bodies. We’re trying to figure out: How do we get people to care?”  

Salt piles are stored on Jones Island in Milwaukee earlier this month. Roughly 2.2 billion pounds of chloride flushes into Lake Michigan each year, according to a recent study.

Wisconsin's waters are getting saltier

Data collected over the last few years show Wisconsin’s waters have been getting saltier for decades. Chloride levels are rising at all of the 43 river sites where the DNR conducts long-term monitoring across the state – most seeing increases between 1% and 4% annually and some more than 10% annually. That kind of change adds up quickly.

At the DNR monitoring site in Lynxville, about an hour south of La Crosse, chloride levels in the Mississippi River had increased from about 12.7 milligrams per liter in 1982 to about 21 milligrams per liter in 2020, according to a 2021 study from Mississippi River water quality specialists with the DNR. That’s a 66% increase.

A forthcoming study from the Upper Mississippi River Basin Association found that chloride levels have increased at least 35% between 1989 and 2018 across the entire upper basin, which extends from the river’s headwaters in Minnesota to southern Illinois. 

Lake Michigan has become about 7.5 times saltier since the 1800s, according to one study. And more than 70% of the lake's salt pollution comes from discharges involving just five rivers: the Fox and Milwaukee rivers in Wisconsin and the Grand, St. Joseph and Kalamazoo rivers in Michigan. 

Although the larger rivers bring in a lot of salt, they also bring in a lot of water, making the share of chloride small compared to the total amount of water flushing into the lake.  

Even bigger problems exist in the smaller tributaries – some so small they don’t even have names – that drain into the lake, said Rob Mooney, a freshwater scientist and author on the study. Because they don’t have as much water, their concentrations can skyrocket.

These smaller streams often get overlooked, but “they’re still important ecosystems in their own right,” Mooney said.  

“Even though Lake Michigan as a whole isn’t becoming the next inland saltwater lake, these streams could have some harsher impacts sooner than the actual lakes.”

Freshwater salinization syndrome

The concept of freshwater becoming saltier, known as freshwater salinization syndrome, isn’t unique to Wisconsin or even 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 the DNR set limits for when chloride becomes toxic to aquatic life. Wisconsin’s are more up-to-date than the federal limits, which haven’t been updated since 1988. In Wisconsin, 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. 

Fifty-one Wisconsin rivers and one lake are considered chronically impaired by chloride under those standards, according to DNR data – most in the southeast region of the state. More than half of the water bodies on that list were added since 2016. 

In the Milwaukee River Basin alone, 117 miles of waterway currently have chloride levels that are considered impaired, according to data from Milwaukee Riverkeeper. 

Lincoln Creek, which flows through the city’s North Side neighborhoods, and Wilson Creek, which drains urban land including the airport, have had chloride levels that are five times the level instantly toxic to fish. The creeks downstream of Interstate 94, like Honey Creek, also have notably high levels. 

On the western side of the state, the aim is to prevent waters from reaching those chronic toxicity levels, said Shawn Giblin, a DNR Mississippi River water quality specialist who coauthored the 2021 study that examined chloride concentrations at Lynxville. 

But with increases building up fast, that may be a tall order, especially in the steeply sloped Driftless region where stormwater runs quickly down hillsides.  

More:Ice is a major barrier to Great Lakes shipping. New legislation is delivering a $350 million icebreaker to keep the waters open.

More:Hold the salt: Organization asks Wisconsinites to cut down on use of rock salt this winter to keep state waters clean

A handful of road salt is shown Tuesday, December 13, 2022 on Jones Island in Milwaukee.

Chloride's adverse impacts

Toxic amounts of chloride can kill aquatic plants and animals quickly, Giblin said. That includes zooplankton, microscopic animals that feed on algae. If they’re killed off by water that’s too salty, it makes conditions ripe for harmful algal blooms — overgrowths of algae in the water. 

Fish can even dry out if the water is too salty, said Cheryl Nenn, who manages the water quality monitoring program for Milwaukee Riverkeeper. This can reduce fishery quality and size, or kill them altogether. 

And too much road salt can change how a lake mixes, Mooney said. Because saltwater is more dense than freshwater, the salt-polluted water will sink to the bottom. Sometimes it will stop the lake from mixing altogether and even starve the water of oxygen so that fish and other organisms can no longer live on the bottom. 

Chloride also exists in the state’s groundwater, the drinking water source for about two-thirds of Wisconsinites, according to the state health department. Less than 2% of Wisconsin groundwater samples from the last 20 years had chloride levels above the enforcement standard set by the state of 250 milligrams per liter, according to data from the DNR’s Groundwater Retrieval Network. But the other component of salt – sodium – could pose a bigger health problem in drinking water for people who are on low-salt diets. 

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

And this isn’t just a problem in the winter, experts say. There is an immediate influx in the winter when the salt is applied. But there is also an influx when it's washed into the water by rain, or when it thaws. And there is a lag effect, which is why high chloride levels are also found in the summer months. 

“One of the concerning parts is when it gets in the watershed, it stays there for a while. It stays in the ditches. It gets into the soil. It makes it into the groundwater,” Mooney said. 

Fear of slip-and-fall lawsuits

People tend to think of municipal and county governments when it comes to salting, said David Strifling, the director of the Water Law and Policy Initiative at Marquette University. But as much as half of salting happens on private property, like private roads, driveways, sidewalks and parking lots. Owners of those lots, or the private contractors hired by them, are worried about people slipping and falling, and possibly filing suit. 

“When you’re faced with that kind of liability, your natural instinct I would suspect is to just put down more salt so you can prove you weren’t negligent,” Strifling said.

Another problem: Salt isn’t priced into the contracts with those private property owners, it’s an added charge. That can give contractors a financial incentive to use as much as they can, he said.

New Hampshire is one state paving the way for other snowy states with a limited liability waiver law that went into effect in 2013. This requires contractors to go through mandatory training in best practices when applying salt. If they become certified, they are immune to slip-and-fall claims as long as there wasn’t gross negligence. 

In Wisconsin, state Sen. André Jacque is drafting similar legislation, which would ask the state to create a certification program for commercial applicators and protect those certified against lawsuits. 

“It’s become clear that more is not always better when it comes to road salt, but we need to help training catch up to that fact,” Jacque said in an email. 

Some states have training programs to educate salt applicators about the proper amount of salt to put down. In Wisconsin, the group Wisconsin Salt Wise offers certification classes for public and private road maintenance workers on how to calculate the precise amount of salt needed to keep pavement safe. 

If enough people know that calculation, it can make a dent in the problem. In Minnesota, whose pollution control agency offers Smart Salting training, organizations that participate have been able to reduce their salt use between 30% and 70%, according to the agency’s website

That education can also be applied on a personal level for people’s driveways and sidewalks. Only one coffee mug worth of salt is needed for an average 20-foot driveway or 10 sidewalk squares, Nenn said. 

“If you hear the salt crunching under your boots, that’s too much,” Strifling said. 

Leftover undissolved salt can be swept up and used on the next icy day, Nenn said. 

Making people aware of the problem

A limited liability bill is just one potential tool amid many to decrease salt use – and several others are already being put into practice by Wisconsin’s road crews. 

Brining, where salt is mixed with water before being applied to roads, cleared Wisconsin highways faster and resulted in a 23% reduction in salt use on average, an April study from the University of Wisconsin-Madison found. Some counties even use beet juice as a brining agent to allow the solution to work at colder temperatures. 

Most people don’t realize that standard road salt doesn’t work if it’s below 15 degrees outside, Nenn said. 

Brining is combined with other techniques, like pre-wetting salt so it doesn’t bounce off roads and using underbody plows that can remove hard-packed snow and ice better than plows with a front blade. They resulted in a 30-year low in salt use across Wisconsin roads during the 2020-’21 winter season, according to the state Department of Transportation’s winter maintenance report from that year. 

Going forward, communication about the problem will be crucial, Haydin said. For example, the EPA has convened a group of cold-weather states to help them share information about easing the impacts of winter road maintenance on the environment. 

The most important thing will be to get the message out to the public about the consequences of too much salt.   

“It only takes a teaspoon of salt to permanently pollute five gallons of water,” Nenn said.

And when it comes to traveling on days where the roads may be slick, Strifling said, people need to manage their expectations. 

“It’s a bit unrealistic to think that you’re going to drive 65 miles an hour on the freeway immediately after a snow storm,” he said.

Madeline Heim and Caitlin Looby are Report for America corps reporters who write about environmental challenges in the Mississippi River Basin and the Great Lakes, respectively. Contact them at mheim@gannett.com and clooby@gannett.com.

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