When winter snow arrives, the road salt comes out.

Salt, or sodium chloride, has been used to help keep highways clear in the winter for almost as long highways have been around. New Hampshire is credited as the pioneer, spreading the chemical on its roads beginning in 1938.

By lowering the freezing point of water, salt causes snow and ice to melt, making travel easier and safer. It’s no surprise that a tremendous amount of salt is used for deicing today. In fact, more than 40% of the salt used in the U.S. is spread on roads and parking surfaces. It amounts to more than 10 times as much salt as is used in food production.

But while road salt is helpful for drivers and pedestrians, it can harm the environment and degrade infrastructure. The chloride in salt is toxic to aquatic life and vegetation, and there’s no natural process that breaks it down to prevent it from building up to dangerous levels. Salt also corrodes buildings, vehicles, roads and other infrastructure. Estimates have placed the cost of road-salt-driven corrosion in the billions or even tens of billions of dollars per year. 

And the consequences of salt-driven infrastructure damage can be even worse. According to the American Chemical Society, road salt was a key element of the Flint, Michigan, water crisis. In 2014, the city switched to a water supply that had an unusually high concentration of chloride from road salt runoff. Because the city's water plant wasn't treating the water to control corrosion, the chloride quickly damaged old pipes, allowing extremely toxic levels of lead to leach into the municipal water.  

That’s why scientists are concerned that the world’s waterways and soils are getting much saltier. We're always building new roads and surfaces that need to be deiced, and research suggests that people are also using more salt to do the same job in the areas they need to clear. 

And while you might think that the majority of environmental road salt comes from deicing highways and other major roads, that’s not necessarily true. In studies of chloride-impacted waterways, the single largest source of road salt was private roads and parking lots.

This means that using road salt responsibly can make a real difference, even if you’re only clearing a parking lot. You can limit the damage caused by road salt runoff – to the environment and to your business infrastructure – while keeping pavements and walkways safe for drivers and pedestrians.

What You Can Do

The first thing to know is that you probably need less road salt than you think. One rule of thumb is that when you spread the salt, the grains should be about three inches apart. Another rule of thumb is to use one cup to one-and-a-half cups of road salt per every 250 square feet, which is about the size of two parking spaces.

Here are some more tips to use road salt in a way that limits the damage to infrastructure and the environment:

• Use a plow, shovel, broom or snowblower to remove snow before applying salt. Don’t use salt to burn off the snow.
• Sweep up excess salt and save it to reuse later. At season's end, you can save salt for next winter.
• Remember that as long as you're using an adequate amount of salt, spreading more won't make the snow melt any faster.
• Don't put salt where you don't need it. When using broadcast spreaders, make sure the salt isn't going further than you want it to by installing a deflector. Or for the most control of where the salt is going, use a drop spreader.
• Calibrate your equipment by measuring how much salt it spreads at different settings. Calibrate it once a year, after equipment maintenance and when changing from one type of salt product to another. For detailed guidance on equipment calibration, see chapter six of this guide from the Smart Salt Collaborative.
• Pay attention to the temperature. Rock salt isn’t effective below about 15 degrees F, and remember that what matters is the pavement temperature, not the air temperature.
  You can assess pavement temperature using an infrared thermometer. Rock salt will be wasted on pavements that are 15 degrees F or below. At those temperatures it makes sense to use a commercial ice melt instead.
• Consider making a deicing brine by mixing water and rock salt. Brine starts working more quickly than dry salt because the salt doesn’t need time to dissolve, and it eliminates bounce and scatter from salt spreaders. Typically, applications of brine use less salt than applications of dry product. You can spray brine from a backpack or hand-pump sprayer as long as you clean it of any herbicide or pesticide first, according to the Smart Salt Collaborative guide.
• The Smart Salt Collaborative guide also suggests limiting access to road salt, because people who aren't properly trained may tend to use too much of it. Don't keep a bucket of road salt in your business's entryway – or if you do, take steps that encourage people to use the right amount. For example, you can keep a small scoop in the bucket, avoid filling the bucket completely and create signs explaining when and how the salt should be used.