Photo by Laura Pratt.

Balancing Water Quality with Safety: How Municipalities Use Salt on the Roads

Plows patrol the streets in Winooski, VT after winter storm Harper’s heavy snowfall. Photo by Laura Pratt.

In the fall, LCC attended the Lake Champlain Watershed Deicing Conference organized by Lake Champlain Sea Grant. The conference brought together private contractors, municipal staff, watershed groups and interested citizens to learn about the state of chloride in the Lake Champlain watershed and best winter management practices for reducing the flow of salt into our waterways. The following article discusses how area municipalities handle our region’s snowy roads, the environmental concerns associated with salt use, and new methods and technologies emerging in the snow removal industry to reduce salt usage.  

After winter storm Harper dumped over two feet of snow in parts of the Lake Champlain watershed, followed by more precipitation in the form of freezing rain, the roads were slick from both snow and ice. The few cars braving the weather might find themselves outnumbered by plows, earthmovers, and dump trucks. While the sudden appearance of plows and clear roads after a storm may seem like magic, the snow removal process takes careful planning. Even before the Lake Champlain basin’s heavy snow comes down, or freezing rain coats the roads, municipalities are already swinging into action.

While you may not have been thinking of snow removal in the fall, municipalities and plowing companies spend that time getting prepared. Salt spreaders – mechanisms that are usually attached to the back of a plow – are calibrated before any snow comes down to make sure they’re operating at peak efficiency, and that they’re spreading what the truck controls say they’re spreading. The method of calibration is simple: the salt spreader is set to lay down a certain amount of salt per square meter, and it is run across a designated number of meters of non-porous pavement. The salt is then swept up and measured, and if the math adds up the machine is good to go. If the actual salt laid down is more or less than anticipated, however, the salt spreader’s mechanism may have to be tweaked over a few more trial runs until it’s measuring the salt accurately. During this period of machine calibration, personnel are also trained on how to target their use of salt to the conditions: less for level stretches of road in mild weather, more for hills, sharp corners, and severe weather.

Members of the Fall 2018 De-icing Conference gather to view a salt calibration demonstration. Photo by Laura Pratt.

Calibrating salt spreaders is vital to reducing the amount of salt used overall, which is both good for business and makes environmental sense. While it is still the cheapest and most effective means of melting ice, salt does plants, animals, and drinking water no favors. Routine, and often excessive, use of salt has built up in the Lake Champlain watershed over the years, which can cause a host of problems. Salt damages plants’ ability to absorb nutrients, and can affect aquatic life if it’s washed into a water body. Chloride (salt) pollution also contaminates drinking water and damages infrastructure. Some invasive species, such as Eurasian Watermilfoil, aren’t harmed by higher chloride levels and can out-compete native species. As is the case in many Northeastern lakes, chloride levels in Lake Champlain have been steadily increasing since long-term monitoring started in 1992. A study by the Global Lake Ecological Observatory Network (GLEON) in 2017 found that chloride in Lake Champlain measured 11.528 milligrams per liter. This is a much higher level than other lakes studied in Vermont and upstate New York, the vast majority of which measured under one milligram per liter.

With their machines calibrated and their personnel trained, municipalities are ready to handle whatever nature throws at them. Thanks to modern meteorology, we can now count on some warning before a major snow or ice storm arrives. Before the storm even hits, trucks are already out on the road, spraying the pavement with the first line of defense: anti-icing fluid. Anti-icing fluid is usually a salt brine (23% salt and 77% water), although it can contain other components to maximize efficiency. The fluid acts as a bond-breaker to prevent ice from sticking to the pavement, which makes it easier to plow up after the storm. It’s much like spraying a pan with grease before cooking.

Because anti-icing fluid contains water, however, there are some limitations; it cannot be used when temperatures fall below 15°F, because air that cold will freeze the brine itself. It is also not typically used before a freezing rain, as the rainfall itself would wash the fluid away before it could be useful. That makes handling wintery mixes, like the sleet brought by this year’s storm, tricky. Rain will wash the brine away, while following temperature plunges makes later application dangerous. One solution is to sprinkle dry salt as soon as it’s cold enough for the rain to turn to snow, which turns the puddles of rain and slush itself into a brine.

As soon as the snow has stopped – or periodically throughout the storm, on busier roads -  plows are there to clear it away. This follows a principle that you may have experienced while shoveling your own walk at home: the earlier you get it off the pavement, the less likely the snow is to be trampled down and frozen into a sheet of ice.

If the worst does happen, however, and ice forms on the roads, there are still things municipalities can do to make the streets safe for driving. Salt brine isn’t just useful as an ice deterrent – wetting salt before spreading it over the ice actually increases its ability to melt the ice that’s already formed. Just wetting the salt can reduce the amount of salt needed by 20%.

Salt works by pulling water molecules out of their ice formation, which melts the ice into a liquid brine. When the salt is already a brine it has a larger surface area, and works a lot faster. Wetting the salt, distributing it as salt brine, and moving slowly as it’s spread can help it stick to the pavement and reduce the amount of salt that scatters off the pavement. Some municipalities are also using automatic vehicle location technology, which allows plow drivers to show their current location, and gives them information on where salt has already been spread.

Shoveling your walk right after a snowfall is an important step toward using less salt. Photo by Lori Fisher.

There are alternatives to salt, but they are more expensive and have a different application. For example, acetates are biodegradable and have a lower freezing point than salt (calcium magnesium acetate freezes at -18°F, and potassium acetate freezes at -76°F). However, acetates contain high levels of nitrogen and phosphorus that lead to cyanobacteria blooms in the Lake Champlain watershed. Another option, sugar beet juice, can be mixed into salt brine to increase its effectiveness. Municipalities in big cities like Toronto are just starting to incorporate this sugary by-product into their snow removal routine. However, large-scale use of sugar can be prohibitively expensive, so the sugar beet trucks are still a work in progress.

Municipalities work hard to keep the roads clear during the winter. There are things you can do to help them out in reducing the amount of salt needed for the roads. One of the unrealistic expectations we often have is for the pavement to stay bare and completely ice-free all winter. Ice and snow are a reality of winter driving, and trying to stop them entirely uses up a lot of salt and a lot of tax dollars. Even in the private sector there are misconceptions about how much salt is enough for sidewalks and parking lots (click here to read LCC’s clean lake tip on reducing your own use of sidewalk salt). Falling on the ice is dangerous, and when in doubt you should err on the side of safety. However, you do not need to feel the “crunch” of salt underfoot for the sidewalk to be safe. A little bit goes a long way, especially when it’s applied as a brine.

Another unrealistic, and unsafe, expectation is that you can retain the ability to drive fast during the winter. Slick spots on the road form quickly in the right conditions, and ice can be invisible, especially at night. If possible, avoid driving when travel is hazardous. If you must venture out on snowy or icy roads, slow your speed for the conditions and increase your following distance in bad weather. Learn ahead of time whether your car has an antilock brake system, which is designed to prevent your wheels from locking up while braking. If you do have antilock brakes, apply firm continuous pressure to slow down. If you do not, gently pump your brakes as you stop. For more winter driving tips, visit the National Highway Traffic Safety Administration’s website or download their handy write up

Luckily for the Champlain watershed, municipalities are continually fine-tuning their snow and ice removal methods to reduce salt pollution. Studies in the Great Lakes region indicate that most of the non-point source chloride pollution in fresh water originates on private land and parking lots. By simply being mindful of your salt usage this winter, and your snow removal expectations, you can make a positive difference in the Lake Champlain basin.