If you live in a place with both cars and snow, chances are you’ve witnessed first hand the annual salting of the roads. Since at least the 1940s, Americans in the snowy states have salted annually, often many times a year, in an effort to make our roads safer. Ask anyone who has spun out while driving, or unwittingly hit a patch of black ice: slippery roads are nothing to scoff at, and salt can be a necessary, even life-saving, tactic for winter road warriors.
The problem is, salting the Earth is something of a Biblical notion: it’s what one did to an enemy to make land unproductive for agriculture.
In the 20th century, salt transformed from ancient warfare tactic to an economically necessary step that has kept the country’s industrial engine revving. Salt’s new job became keeping U.S. roads open at whatever cost. The economy depended on it.
But now, those Biblical results are manifest: The environmental damage must be reckoned with. Yet, we simply cannot afford to go salt-free.
Today, shutting down a state’s roads due to winter weather can cost hundreds of millions of dollars, says Michael Smith, technical training specialist with Bay State Roads at the University of Massachusetts Transportation Center. For example, shutting down the roads of Massachusetts (as happened statewide during a 2013 nor’easter) can cost between $300 and $700 million dollars per day, Smith says.
And so, as a nation, we dump 22 million tons of salt every year on our roads.
Fish, animals, insects, plants and algae have changed their behavior in response to the current levels of road salt washing into their habitats. Some species of frog are, incredibly, changing sex as a result of these massive doses of salt. High enough doses can kill them and other wildlife. For the naturalist, folks who like to fish or otherwise enjoy nature, and for locals who rely upon natural tourism, salt’s side effects can’t be ignored.
A hybrid beet juice-salt water brine is helpful to coat asphalt in advance of a snowstorm to prevent precipitation from sticking to the roads. (AP Photo/Gene J. Puskar)
Salt runoff also makes its way into our drinking water supply. It corrodes our pipes, which leads to higher levels of lead, manganese and mercury (among other heavy metals that are all toxic to humans) in our drinking and bathing water. Experts agree that exposure to such high levels of salt can even be problematic for people required to eat a low-sodium diet.
Perhaps more relevant to the pocketbook is the effect of salt on our vehicles: That rust on your car? Salt. The road deterioration that damaged your car? Salt. Or perhaps more specifically, magnesium chloride. In fact, the umbrella term “road salt” refers to any one of three chlorides: sodium chloride (rock salt), magnesium chloride and calcium chloride.
Dr. Rick Relyea is the director of the Darrin Fresh Water Institute and the Jefferson Project at Rensselaer Polytechnic Institute in Troy, New York, which has been studying the effects of road salt since 2014.
Relyea stresses, “It’s undeniably important for safety to remove ice.” But at what cost?
“In general, what we now know as road salt can be lethal to a wide variety of plants and animals, and as is always the case, it depends on the dose,” Relyea says. “So if we have high amounts of road salt we can kill all kinds of plants and animals. In different parts of the world it’s different.”
In the last five years as public awareness of the problems with these chlorides has grown, municipalities nationwide have responded with changes that, they hope, will be cost effective, good for the environment and good for public safety.
In Lake George, New York, environmental research has uncovered surprising and significant damage to the natural world, and has inspired a shift in how roads are salted. In Cambridge, drinking water is so heavy with salt runoff that coffee machines are corroding, and the city seeks to mitigate the problem both within their own city limits and in neighboring towns that affect their watershed. And in Helena, Montana, concern over salt’s effect on the environment — and cars — has inspired a program that takes recycling to new levels.
In Lake George Village, New York, says Relyea, they use a brine, applying it to the road before a snowstorm, which makes it harder for the snow to stick to asphalt and easier to remove by plow.
Brining might sound like something you do to meat before a holiday meal, and it’s a similar principle employed here. A brine is made of, for example, 80 percent water to 20 percent salt, and then that is what is put down on the pavement before a flake ever falls. Brine prevents the snow from sticking, making it easy to plow, and it prevents black ice from forming. Many municipalities have their own brine “recipe” that can be tinkered for local conditions. Often that recipe calls for “a little carbohydrate,” as more than one expert told us.
Carbohydrates — meaning, essentially, sugar — lower the freeze point. Beet juice is the go-to in some places, while others experiment with molasses, corn, and soybean oil. It’s the sugar that makes the brine sticky and effective at low temperatures. Think the same principle as putting a Coca-Cola or a bottle of vodka in the freezer; neither will completely freeze. In that way, the brine recipe really is, well, a recipe.
If you brine the road first, the snow doesn’t stick and the road can become dry asphalt quickly. If you pour rock salt on top of already fallen snow, more salt needs to be used, and then the snow melts top-down, waiting for vehicle tires to crush the salt and mix with the snowmelt to become brine anyway — rock salt doesn’t do anything to the snow unless it goes to a liquid or a brine state. Applying pure salt after the snow has fallen takes more time, more salt, and can leave lower layers of snow stuck to the pavement, because, you’re melting top-down instead of (as with the brine) bottom-up.
The Jefferson Project uses a network of high-frequency sensors, including this vertical profiler, to obtain real-time data on the movement of water and pollutants through the Lake George watershed. (Photo courtesy Jefferson Project)
In addition, says Relyea, Lake George changed the edges on their plows. A standard plow, probably ten to 12 feet wide, typically leaves snow in those dips asphalt roads incur. The plow is unable to follow the natural curves of the road. So the community started using a “live edge” of 5 smaller plows mounted on springs, so it can fit the contour of the road, and remove more snow.
Making these two relatively small changes has reduced the amount of salt used in Lake George by 30 percent in the last few years, which, says Relyea, is a big improvement.
The vast majority of salt Lake George uses is sodium chloride. But is that really safer than, for example, calcium or magnesium chloride? “Not really,” says Relyea. “Depending on what species [of plant, algae, fish, reptile or animal you’re talking about], some [chlorides] are much more lethal to plants and animals than others, and it’s not always the same one each time.”
Take the rainbow trout. Calcium chloride is worse for the fish than sodium chloride, he says. Magnesium chloride is bad for the fish too. “Which plant or animal [you talk about] depends which [road chemical] is worse.”
“Impacts are, in some cases, pretty straight forward,” says Relyea. “Salt does things to animals no one would have guessed.” For example, when wood frog tadpoles are exposed to high concentrations of salt, their sex can change. “No one had that expectation,” says Relyea.
“What’s really concerning [are the] groups of animals particularly sensitive to salt,” Relyea adds. “Zooplankton eat algae. They’re the reason a lake is clear. We’ve seen in Canada, where it only takes 50 milligrams [of salt] to kill them off.” Bigger fish eat those zooplankton, and then bigger fish eat them, and so forth. In an ecosystem built upon those zooplankton, that food source dying off is a problem.
“We need to be concerned about that,” says Relyea. “There is some level of hope. And that is that some animals can rapidly evolve higher tolerance to salt, within a matter of months. They are more tolerant than three months earlier. You can still kill them,” Relyea adds. But, “they’re a little more tough. It does suggest, others might have that ability. This ability to evolve might buy us time [with some species], but some things will not evolve and will die.”
And then there are the unintended trade-offs if species do evolve tolerances to road salt. Plankton, says Relyea, “evolve, but no longer have a circadian clock.” That clock previously dictated things like when to surface and when to go deep, all to avoid predators. The loss of the circadian clock makes them a sitting duck for predators. “That’s a huge impact,” Relyea says. Again, he notes, “Not at all something we expected to see.”
Another alarming consequence Relyea cites is the increasing salinization of the Great Lakes, where invasive, salt water-friendly species such as zebra mussels are doing well now. If the Great Lakes get saltier, invasive species will likely do even better.
Back at Lake George, the spring snowmelt runoff brings a mega-dosing of salt. During a spring rain or melt, Relyea says that salt levels in streams can spike to 2,000 milligrams of chloride per liter of water, instead of the 230 milligrams of chloride per liter of water limit dictated in EPA guidelines. (Canadians, he notes, have set the bar even lower, at 140 milligrams per liter.) Relyea says they don’t know what the effects of such short-term, massive spikes are yet. The short-term guideline set by EPA is 860 milligrams per liter, he notes. “We expect it causes lots of harm.”
Lake George is a key driver of the Adirondack region’s $2-billion tourism economy, so preserving the natural environment is important. Clear roads and a healthy ecosystem are crucial for seasonal tourism. To “put the whole watershed on a low-salt diet,” Relyea says, is a win.
Cambridge, Massachusetts, home of both Harvard and MIT, has its own water source, separate from many of the Greater Boston area’s systems. But the town’s drinking water reservoirs are affected by multiple lanes of high-speed, high volume traffic on Route 4, in addition to the 225,000 to 250,000 cars that travel Route 128 every day. Under those conditions, and during a snowstorm, road salt crews are in high demand and can get stuck in traffic, which makes de-icing more difficult. The need to keep busy roads safe for travel makes the watershed more prone to high salt content. A look at Cambridge’s water quality report over several years shows sodium content from road salt runoff to be a significant water contaminant.
For Cambridge coffee connoisseurs, the chlorides in the water mean trouble for the machines that brew their high-quality coffee. Even machines under warranty won’t be covered when subjected to salty water. “Under heat and pressure, chloride becomes acidic and corrosive. This means the equipment doesn’t last as long as it should,” reports local NPR outlet WGBH.
Stephen “Sam” Corda, Managing Director of the Cambridge Water Department, is responsible for keeping Cambridge’s water clean. “In general, it’s chlorides,” he says of what’s in Cambridge’s water. “Magnesium, sodium, calcium chloride and some sulphate. It’s increased over time due to de-icing materials [entering] our watershed.”
Salt runoff from residential use contributes to the problem as well — the salt we all put down on sidewalks and driveways to make sure neighbors and postal carriers don’t slip and fall. But the problem is not so much Cambridge residents as it is the local and state departments of transportation and other municipal entities that spread copious amounts of salt within the 24 square miles of the town’s watershed.
Paul Brown, former director of snow and ice for the Commonwealth of Massachusetts for almost 9 years, managed rural and urban, high-speed and low-speed roads and was also the chairman of Clear Roads, a research group dealing with snow and ice issues. He’s retired now, but others in the road de-icing industry who care about the environment still point to him as a leader on the issue.
Brown says he’s encouraged Mass DOT to do direct brine applications in an effort to reduce total sodium chloride use. (Mass DOT — following a trend in many state and local governments nationwide — declined numerous specific requests to speak with an official directly for this story.)
Cambridge's brine-manufacting facility aims to reduce salt usage on roads and cut down on the amount of salt in the city's water supply. (Photo courtesy TJ Shea)
Places with high-speed, high-volume road traffic are treated differently than less-traveled roads in upstate New York, Brown says. With high-speed, high volume roads, the demand from the customer for fast and clear roads, necessitates striking a creative balance in how everyone’s needs are met.
“We should be looking at a minimal chloride brine with minimum enhancement,” Brown advises.
The initial application of a well-crafted brine can reduce the amount of salt used from 300 pounds per single-lane mile down to 80 to 90 pounds of salt per single-lane mile. Some experts interviewed for this story say they’ve even seen upwards of 500 pounds of straight-salt application used per single-lane mile.
This kind of change, notes Brown, is not cost-prohibitive. In fact, brining before a storm can save a transportation department 30 to 40 percent of a materials budget, meaning for every $60 of salt, $20 could be saved.
That argument might resonate a bit more than, for example, expressing concern for the effects of high sodium chloride on zooplankton.
“Change is difficult,” says Brown, especially for a department of government tasked with public safety.
Accountability is also a key factor. The need to monitor how much salt or brine the trucks are applying is important, too. A simple recalibration of the truck can save hundreds of dollars in materials, not to mention the environment.
Corda works with the municipalities in the Cambridge watershed to help shift their de-icing practices. Still, in the absence of hard data from these communities that would support his recommendations, he’s not that assertive about the changes that need to be made. The last serious study on the source of chlorides here was done in 1985, he says. MASS DOT is conducting another one, adds Corda, expected to be completed by late 2021.
“If a municipality becomes the primary source [of sodium in the Cambridge drinking water], and the report says that, we have a bigger hammer,” says Corda, to encourage another municipality to make changes.
T.J. Shea, Superintendent of Streets for the City of Cambridge, says the city is trying to use less salt, which he says, “hurts the trees. It hurts the pavement.” Shea says the city of Cambridge experimented with making its own brine last year, and is now building their own facility to manufacture the brine. They will apply it themselves in a proportion that will preserve Cambridge’s water, decrease costs and possibly save its coffee machines, too.
But neighboring communities need to make some efforts, too, note the experts. The Cambridge water supply isn’t isolated from the rest of the region.
Here in Big Sky Country, brining isn’t an option for Helena’s department of transportation. “We have local opposition to using brine on the roads,” says City of Helena Transportation Systems Director David Knoepke. The public, he says, does not want to face the environmental effects of salt, in addition to the damage that salt can cause to vehicles. “We’re close to major rivers, reservoirs and lakes,” Knoepke explains.
Instead of brine, Helena uses traction sand mixed with chips from chip-seal projects — the gravelly, aggregate rock you might have driven over that gets pressed into a smooth road surface the more vehicles drive over it. Come springtime, the remaining sand and chips get swept up and recycled for the next winter. This process can generally reuse the sand mixture for 3 to 4 years.
“We pay for the chips so we might as well use them,” Knoepke says. What is Helena’s particular de-icing recipe? “We do mix some salt in the sand, a single-digit percentage. We apply that on our roadways, do use a little mag chloride, spray a bit on the sand before it goes on the roadways, it helps to stay on the roadways.”
In Helena, Montana, trucks spread a traction-enhancing mixture of sand and gravel chips on the roads. (Photo courtesy David Knoepke)
They procure the chips from their own projects, sweeping up the leftovers after the rock was rolled out on a road project. Every time the chips — or chip de-icing mix — goes for reuse, it gets tested for VOCs, to ensure it will not cause any health issues.
“When you put something on the roadways, you’ve got all these vehicles leaking oil, antifreeze, gas, whatever, and that’s what they’re testing for because there can be hydrocarbon remnants,” Knoepke says. “We test to make sure it’s clean when we put it back on the roadways. We’re the only ones in Montana who do that.”
Perhaps not surprisingly, this process also captures a lot of leaves and other foliage along with their winter sand, so they run the sweepings through a screener until it becomes too dusty to be usable.
“We’re trying to reuse [materials] to the benefit of the citizen and a reduced cost,” says Knoepke.
In addition, they don’t spread the winter traction sand mixture throughout the city. “For the average storm, we only sand the intersections and hills,” says Knoepke. “We don’t spread it constantly down a lane mile, like some do with liquid de-icer [brine]. We use it sparingly, when we need it, or if we get a sanding request for a hill or a police department.” Usage also depends on the storm. “If the roads are getting slick, then the guys are putting down more. We try to do the best job for the citizens of Helena, in the most economical way we can.”
Across the lower 48 United States, the blowing, blustery snow of the Plains is much different from the wet, heavy snow of the Great Lakes. And the nor’easters that hit New England are different events all together. Each place has to deal with the conditions, and environmental factors, differently in order to ensure public safety. When it comes to buses trying to get kids to schools, emergency vehicles, or regular folks getting to work, rock salt and liquid salt brine are still the most effective de-icers available.
Laura Fay is part of the winter maintenance research group at the Western Transportation Institute at Montana State University, studying the environmental impacts of de-icer, testing new formulations, and identifying best management practices.
“Any de-icer product has an impact,” says Fay. “It doesn’t matter what you’re going to do. It still has an impact.” Even Helena’s sand mixture could be problematic, says Relyea, who points to concerns about the sand being washed into streams and lakes that could potentially form deltas.
Fay’s work is in helping the people tasked with the job to understand: “If you’re applying the right material at the right time, you’ll save on product, money, and time.”
Equipment calibration alone, she says, can save $25,000 per salting season right off the bat.
“Human safety, cost, environmental—it’s a blend,” says Brown. “Changing a piece of equipment might cost money up front, but if it saves you in the course, it’s a good investment.”
“Only recently has sustainability and environmental stewardship come in,” Fay notes. She encourages folks to partner with other agencies. “You can say you want to reduce chlorides in the environment, in the waterways, but if you don’t monitor, you don’t know” if your efforts are working.
“One of the things we’re working on now is to have predictability,” says Relyea, in terms of how long it will take to restore the environment after decades of salting it. “How long will it take to restore? It will not be immediate. If we stopped using salt entirely, there will be salt coming out of [the] soil for years.”
Still, notes Relyea, an improvement can be seen quickly, within 1 to 2 years. “You can’t improve global warming in that amount of time. This is an issue that can be remediated to a substantial degree if we get everyone on board.”
After all, we’ve been loading up salt on the roads for decades. It’s past time to start to get rid of it.
“Snow and ice isn’t rocket science,” says Brown. Still, “if you’re in the snow and ice biz long enough, Mother Nature’s gonna kick your butt anyways. She’s gonna win, no matter what you do. The weather will beat you. You just want to make good, informed decisions.”
Valerie Vande Panne is a Next City Equitable Cities Fellow and a freelance writer. She travels extensively throughout the United States. Her work has appeared in Bloomberg, Columbia Journalism Review, In These Times, and Politico, among many other outlets. She is a former news editor of High Times magazine, and the former editor-in-chief of Detroit's alt-weekly, the Metro Times.