Road salt: A necessary evil in short supply
Ever since the New Year's Day major ice storm followed by minor storms, Thetford residents have been calling the road foreman to ask for town roads to be better salted and sanded. Complaints centered on Rt 132, Tucker Hill Road, and Academy Road, What people learned is that the Town is using salt sparingly — there is a road salt shortage.
Several factors account for this. The recent series of mild winters in the late 1900s into early 2000s led to a lower demand for road salt because states and towns reduced orders, anticipating that this trend would continue. In response, salt mines cut back production and stockpiled less salt. Then unexpected frigid winters returned, sending salt sales from 10.2 million tons in 1998 to 18.1 million tons in 2000 and depleting already low stockpiles. A strike at the world’s largest salt mine in Ontario didn’t help things. While geological deposits of salt are virtually unlimited, maintaining adequate supplies turns out to be another story. Salt production is determined by the number of worker shifts and the operational capacity of the massive equipment that does the mining. Miners are highly skilled and trained. When large numbers of them are laid off due to reduced demand, they are hard to replace when demand surges.
Due to the regional salt shortage, Thetford was unable to stockpile enough salt for this winter. In fact, the town keeps running dangerously low and is using it sparingly while the road crew waits for the next delivery. In a normal year, the vendor would deliver the salt. Now the town sends out its own truck to pick up salt whenever the road foreman learns that some is available. It's not a great situation. In fact, Town Manager Brian Story says this is the worst salt shortage ever.
Ice storms deplete reserves of salt very fast. To be effective, salt must be applied to the road before the storm, to prevent ice from bonding to the road surface. The downside of pre-application is that much of the salt is washed away in the freezing rainfall and is wasted. Pre-treating with solid salt actually relies on the warmth of the road surface to initially melt the freezing rain so that meltwater can combine with the salt to effectively coat the road. It is salt in solution, not solid salt, that impedes the formation of freezing rain ice crystals
Salt that is dumped on top of ice can improve traction when the sun or friction from car tires melts the ice to slushy water that can dissolve the salt and prevent re-freezing. And note that salt only stops water from freezing down to around 15 degrees F. Thus, salt pre-treatment of bridges is generally ineffective because they are colder than the road. Please heed the "Bridge freezes before road" sign! It also explains why salt is inadequate when temperatures are very cold. In these conditions, putting down sand can make the surface rough so that tires don't slip (as much).
The use of salt for road de-icing has grown exponentially in the US. From 164,000 tons in 1940, it rose to one million tons by 1954, then 10 million in 1985, to more than 24 million tons in 2019.
The Northeast is among the greatest consumers of road salt, with five New England states at the top. Per mile of road, between 2015 and 2019, Rhode Island used 44.2 tons, Massachusetts 34.6 tons, New York 28 tons, New Hampshire 25.1 tons, and Vermont 23.3 tons. Multiply that by the number of road miles per state, and the amount is staggering. Moreover, these figures do not include private use of salt by homeowners, businesses, shopping mall parking lots, sidewalks, etc.
Unfortunately salt doesn't disappear after it is applied. It washes off onto the surrounding land with the snowmelt and travels downhill into the nearest bodies of freshwater — streams, ponds, rivers, and lakes where aquatic life is adapted to freshwater. Even mild amounts of salt can kill zooplankton that are the basis of the food chain. These microscopic animals transfer food calories from tiny plants (phytoplankton) to higher life forms like fish. They also control algal blooms and recycle nutrients like nitrogen and carbon. Lakes that are ringed by winter-salted roads suffer loss of water clarity and worsening blooms of algae, including toxic blue-green algae.
Higher concentrations of salt cause alterations in the sex ratio of tadpoles, making them 10% more male. It can also stunt the growth of fish such as rainbow trout. Stunted, small size makes them more vulnerable to predators. Much research remains to be done in this area.
Over 47% of lakes in VT are contaminated with road salt. For some lakes, specifically Lake Mempgremagog, Lake Carni, Lake Rescue, Caspian Lake, Little Lake in Wells, Lake Morey, Ticklenaked Pond, and Shelburne Pond, these levels are on the rise.
Salt also makes its way into groundwater and shows up in private and public drinking water wells. And salty road spray causes the desiccation, browning, and die-back of roadside trees and vegetation.
And that’s not all. There's also a connection between road de-icers like salt and the costly rebuilding of interstate bridges, such as on I-91 in Fairlee in 2025, with entire bridge decks being replaced. Salt causes the surface flaking and peeling of concrete because salt prevents water from freezing and thus prolongs exposure of concrete to water. Thus, more water seeps into the concrete's air spaces. Inevitably this water freezes, expands, and exerts stress on the superficial layers of the concrete, resulting in flaking. It gets worse when salt contains magnesium chloride, a de-icing additive. The magnesium actually leaches the calcium out of concrete. An analysis of bridge decks in Oregon showed that they had lost 40% of their strength due to calcium loss, even though they appeared solid by visual examination.
The steel parts of bridges are also vulnerable to salt and other agents of corrosion. Even though the steel is embedded in concrete, over time moisture, oxygen, and salt permeate the concrete and rusting begins. When steel rusts it expands, cracking the concrete and inviting in more contaminants to make more rust, till the concrete starts to fail. The National Association of Corrosion Engineers estimated in 2002 that the direct cost of repairing and replacing corroded bridges in the US was $8.3 billion per year. A more recent estimate reported by the Federal Highway Administration placed this figure at $13.6 billion per year.
There are ways to reduce the amount of salt applied to roads. One is to use brine that contains 23.3 % salt. It starts working right away to prevent ice from forming and also melts snow and ice.
The Town of Thetford would switch to brine, except the cramped Town garage on its one-acre lot does not allow any space for a brine-making facility. Neither is there a regional, shared facility. Town Manager Story is searching to relocate the Town Garage to a larger lot. If this can be accomplished, he is eager to switch to making and using brine. In the meantime, Thetford will just have to continue the deleterious tradition of spreading salt.