Road Salt & Water Quality

Use of salt to prevent ice from forming on roads has likely saved thousands of lives, but it negatively impacts the environment, including our waterways, and degrades infrastructure, such as buildings and bridges. Lake Champlain Sea Grant partners with scientists, winter maintenance professionals, businesses, and residents to maintain safety while reducing the amount of road salt we use. Learn about road salt and how we can reduce its use.

Diagram showing grains of salt on sidewalk How much salt do we use?

We have used road salt on U.S. highways since the 1930s. At that time, we applied about 5,000 tons (2,000 lbs/ton) of salt on highways per year. Today, we use an estimated 20 million metric tons (2,200 lbs/metric ton) of salt on roads in the U.S. each year. This is enough salt to fill dump trucks bumper to bumper for 8,333 miles! That’s a distance from Burlington, Vermont to Seattle, Washington, back to Burlington, and then back to Glacier National Park in Montana!

How does salt impact the environment?

All that salt washes off roads, parking lots, driveways, and sidewalks and can kill vegetation, move through the ground into drinking water wells, flow into local water bodies, and harm fish and other aquatic life. Chloride can accumulate in a lake or pond, which makes the water saltier over time. In northern lakes, including Lake Champlain and Mirror Lake in Lake Placid, New York, we see increasing chloride concentrations. Researchers have observed salt settling to the bottom of Mirror Lake, where it hinders natural lake processes and shrinks the area of the lake where fish can survive during the summer.

Salt also degrades buildings, bridges, and pipes, costing U.S. communities $200 to $500 million or more in maintenance and repairs annually.

How does salt work?

We most commonly use sodium chloride, often called rock salt, to keep ice from forming on hard surfaces like driveways and roads during the winter. When we spread sodium chloride and it mixes with water, it breaks into its individual components, called ions, which are sodium and chloride. These ions act like referees in a hockey game preventing fights between players; that is, the sodium and chloride ions get in between water molecules and inhibit them from joining together to form ice crystals. The jostling for position of the sodium and chloride ions between water molecules decreases the freezing point of water and minimizes ice formation.

Learn more about how salt melts ice in this short YouTube video by the American Chemical Society.

When doesn’t salt work?

It is important to know that sodium chloride only works to reduce ice formation when pavement temperature gets as cold as about 16F (-9C). Below that pavement temperature, other types of deicers, such as magnesium chloride or calcium chloride, must be used. When these deicers mix with water and break apart into their separate ions, they also create heat that helps keep ice from forming. The chemical properties of sodium chloride do not allow it to work in this way.

What can we do to minimize negative impacts of road salt?