A snow plow works to remove snow and deposit salt on the Kennedy Expressway in Chicago
2014 is off to a snowy, cold start! Without maintenance crews working round the clock to keep our streets clean and safe, conditions would have been far more dangerous. But what happens to the tons of salt that are used to de-ice our roads and sidewalks in the aftermath of a winter precipitation event? As snow and ice melt, the salt crystals dissolve and enter soil and bodies of water like rivers and shallow aquifers.
The most common de-icing chemicals are chlorides—sodium chloride (table salt), magnesium chloride and calcium chloride—that do not break down or go away once they are dissolved in water. While chlorides aren’t harmful to human health, they can be harmful to aquatic plants and animals and are corrosive to infrastructure like roads, bridges and pipes. They also cause the cost of water treatment to rise as the resulting salty taste makes water undrinkable.
The negative environmental effects of using traditional methods of de-icing roads are well-documented in the region at this point. According to a 2012 report released by the Illinois State Water Survey, most rivers, streams and lakes in the Chicagoland region have higher chloride concentrations than what is considered normal for this area. Chloride concentrations have been increasing in the region since the 1960s. The report attributes the elevated concentrations largely to road salt runoff.
Cities and towns in the region have been experimenting with some interesting de-icing alternatives in recent years. Alternatives to traditional rock salt compounds—like molasses, beet juice and cheese brine—are gaining in popularity due to their lower costs and environmental impacts. And they aren’t just better for the environment; they’re better at their job.
“The mixture lowers the effective melting point, stores better in the storage facility and has a texture that creates less bounce coming off of the truck which allows us to use less,” explained Bill Edwards, maintenance superintendent for the Kane County Division of Transportation (KDOT). An effective product means that municipalities can use harmful de-icers at lower quantities—a win for both the taxpayers and the environment. In groundwater-dependent communities like those located in the Northwest Water Planning Alliance area, protecting water resources is especially crucial. Once groundwater is contaminated, it can’t be returned to its original state.
KDOT has been a regional leader in moving away from traditional road salt; they’ve used a mixture that is 80 percent magnesium chloride and 20 percent sugar beet byproduct or corn syrup for around thirteen years. The agency was one of the first in the region to use this mixture, and it has since become popular elsewhere.
“The carbohydrate is stickier,” said Edwards, “and that helps hold brine to the road. There is a longer residual.”
A longer residual—the amount of time salt is present on the road—means less salt has to be used, along with the county having to spend less on overtime and fuel costs. “There is a higher upfront cost that can be scary, but we are spending less on overtime and less on fuel, so for us it costs less in the end,” said Edwards. He added that KDOT got away from using the mixture for a period, but noticed the difference and went back to using the carbohydrate mixture. Because much less of an alternative solution than traditional road salt is needed to be effective, municipalities sometimes overapply. However, over time they find the amount that is most efficient—and most cost effective—for them. More salt does not mean more melting.
Moving away from traditional rock salt can increase public safety, cause less harm to our invaluable groundwater resources and cut municipal maintenance costs. It is encouraging to see Northwest Water Planning Alliance communities moving in an innovative direction. Make a resolution in 2014 to use salt more efficiently and to look into alternative de-icing methods in your community!
the amount of traditional road salt needed to permanently pollute 5 gallons of water
US EPA National Aquatic Life Criteria chronic freshwater threshold for chlorides, equivalent to two-tenths of a teaspoon of salt per gallon
US EPA National Aquatic Life Criteria acute freshwater threshold for chlorides, equivalent to just under two-tenths of a tablespoon of salt per gallon
Chloride concentration observed in several shallow monitoring wells along Interstate 94 during an Illinois State Water Survey study, equivalent to two-tenths of a tablespoon of salt per gallon