Rock salt saves lives by helping tires grip on icy roads. Avoid broken bones when homeowners use it on slippery sidewalks, driveways and parking lots.
And in Kansas, one of the largest salt producers in the country, rock salt generates income.
But it also costs Americans billions by corroding cars and bridges. It adds so much sodium to drinking water in some places that it can affect people’s health. And in some places, toxic levels of salt kill or harm plants, animals and crops.
Experts say we can take immediate steps to reduce this toll without sacrificing road safety. (Read tips for homeowners here and winter maintenance crews here.)
The Kansas Department of Transportation has already implemented some of these measures, including brine spraying ahead of winter storms, a practice that can combat slippery roads with less salt.
And at Wichita State University and Iowa State University, scientists are carrying out research that could change the way we clean our sidewalk in the cold months.
Supported by a $1.4 million grant from the National Science Foundation, they are working to capture some of the salt that pollutes our water — such as salt from the nation’s burgeoning water softener industry — and convert it into an environmentally friendly antifreeze product .
“We save extraordinary lives on the road” by de-icing it, said Wichita State mechanical engineering professor Shuang Gu. “I appreciate this practice. (But over the decades) we have applied road salt exponentially.
The rise of road salt
Americans may like salty food, but we use far more sodium chloride on our roads than on our plates. Its use has increased at a meteoric rate over the past century as we built interstate highways to allow more vehicles to travel at higher speeds.
Today, the United States dumps approximately 160 pounds of salt per person onto roads, sidewalks, driveways, and parking lots.
Groundwater and lakes are in trouble in some places, especially in the north of the country. Because it takes time for salt to worm its way from our roads and ditches to streams, lakes, wells and aquifers, scientists at the Cary Institute of Ecosystem Studies say salt levels in our freshwater could continue to rise for years or decades. even if we immediately stop using road salt.
The prospects for reversing this damage look slim, scientists say, fueling a mad rush to reduce our reliance on this deicer.
Yet salt is cheap. So while alternative substances already exist on the market, they come with higher prices, logistical challenges or other limitations.
This means that salt, especially crushed rock salt, remains the #1 method. #1 for de-icing pavement, says the American Geosciences Institute.
What’s the impact?
For centuries, humans have told stories of conquerors sowing salt in their enemies’ fields. Those may be fairy tales, but the fact that we are salting our watersheds today is not.
The Geological Survey has tracked the effects for more than half a century on streams and other sites in eight states. At nearly a third of their sites, chloride pollution reached toxic levels, on average, a third of the year.
In New York, scientists sampled private drinking water wells and found that most exceeded EPA health standards for salt in water. High salt levels endanger trout in New York City by hampering the lake’s natural water circulation so less oxygen reaches deeper depths.
The Environmental Protection Agency says road salt also requires about $5 billion in repairs to bridges and other infrastructure each year. And it’s a suspected cause of lead pipe corrosion that poisoned the water in Flint, Michigan.
Road salt is also a concern for people with high blood pressure whose local drinking water has higher sodium levels, the EPA says. It kills roadside plants, damages crops, increases erosion, and harms frogs and insects, both of which play important roles in the food web.
Some northern states are taking action. A decade ago, New Hampshire launched a salt reduction program because chloride pollution had become a problem in dozens of its water bodies. The state has reduced demand for road salt by a fifth, the EPA says.
What’s happening in Kansas?
Kansas sits on a salt sea. Literally.
Hundreds of millions of years ago a shallow sea dried up. Today, mines in central Kansas turn those vast salt deposits into jobs and income.
Kansas is among seven states that produce 95 percent of the nation’s salt, says the US Geological Survey. Nationwide, salt is a multibillion-dollar industry. Kansas produces more than $200 million of ore annually.
The Kansas Department of Transportation distributed 83,000 tons of rock salt to protect drivers on state highways during the 2021-2022 winter.
“Our teams feel very responsible when they’re on the road,” said Clay Adams, director of field operations, “to make sure the roads are as safe as possible.”
But the agency has also made changes to address salt pollution.
It has moved its salt stocks to facilities where it can prevent runoff and has begun cleaning its trucks in wash bays to capture the highly salty wastewater for treatment.
“We used to wash them outside, just outside in the parking lot outside our stores,” Adams said.
The agency also makes an effort to calibrate its trucks so they spread the right amount of salt, another important check, says the Cary Institute.
And the agency is increasingly relying on brine, one of the best tricks of the trade for preparing for storms and one that can reduce the need for rock salt after snowfall.
State workers began experimenting with brine in central Kansas in the 1990s, mixing it in a backup tank in one of the garages.
Roger Alexander was a KDOT engineer in Salina at the time with a penchant for trying new things.
So the agency had tasked him with working on a federal project designed to look at different ways of clearing roads in the United States and around the world and determine which worked best under which conditions. Brine can work wonders.
“It would stick to the road better than anything,” he said. “If it started to snow, instead of having the snow packed and frozen, it would melt and basically run off the road.”
The Cary Institute says that proper brine treatment can reduce overall salt use by up to 75%.
Pretreatment with rock salt, on the other hand, does not work. When cars pass, it bounces and scatters.
“Whatever you put down,” he said, “you just wasted it.”
Today, Kansas uses the brine treatment statewide. He also taps into other tricks, like coating rock salt with brine to help it stay put, or adding viscous byproducts of beet and corn processing to his road treatments. These compounds can turn snow into a kind of oatmeal texture that’s easier to plow.
Alexander says engineers and street crews have a long list of factors to consider when evaluating their options. Is the day very windy? Will a storm start with rain and end with snow? What type of plows and how many do you have available? Sometimes rock salt is their best option.
What are Midwestern scientists doing?
Scientists from Kansas and Iowa imagine a new way to keep us safe in the winter by recycling salt found in urban wastewater.
They are working on the production of sodium formate, a non-corrosive de-icer used by airports and military facilities.
Studies suggest that bacteria break down sodium formate, and the compound doesn’t harm the environment the way salt does. (However, part of the four-year plan includes further examination of its effects.)
Substance has two notable drawbacks that the Wichita State and Iowa State teams want to overcome. One, it’s too expensive to use on America’s vast system of roads and highways. Two, it’s made with natural gas, which raises other environmental concerns.
Lead researchers Gu and Wenzhen Li (a professor of chemical and biological engineering at Iowa State) have figured out a way to make sodium formate without fossil fuels.
The process involves concentrating salt from wastewater – specifically, the highly concentrated salt released from increasingly common water softening systems – and using it in a chemical reaction that combines carbon dioxide and salt into sodium formate without the need of natural gas.
This would produce chlorine as a by-product, which could be used for sanitary purposes and swimming pools.
The EPA says scientists are also exploring other approaches to the nation’s salt problem, such as using porous pavements that let water seep through and reduce ice formation in the first place.
Gu calls himself a realist. Solutions will take time. The work of his team will take years. However, with each passing winter, more salt builds up in US waterways. The best tool available today is the public buy-in.
“There are many challenges ahead of us,” he said. “We should go some way to raising awareness…Let people know that there is a problem and that we need to use road salt more responsibly.”
Celia Llopis-Jepsen covers the environment for the Kansas News Service. You can follow her on Twitter @celia_LJ or email her at celia(at)kcur(dot)org.
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