Question: How much salt should I use to melt ice on my driveway or sidewalk?
Answer: As a general rule of thumb, 1 pound of salt (one heaping coffee mug) is enough to clear a 20-foot driveway or 10 sidewalk squares (250 sq. ft.). If there is still salt on the ground once the ice is gone, you’ve used too much. Sweep up and reuse left-over salt to protect lakes, rivers, and groundwater.
Just before Christmas, cold winds blew in from the Arctic, snow glittered in the moonlight, and 5.4 million Minnesotans tried to decide whether they loved or hated winter. When the first round of snow came, my family flocked with others to the sledding hill at Stillwater Junior High where we tumbled down the hill with dog in tow for nearly an hour. The next weekend, when temperatures hit -20°, we holed-up inside baking dozens and dozens of cookies. If all goes according to plan, we’ll continue praising and cursing the winter in equal measures for the next three to four months.
Perhaps no aspect of winter is as tiresome and un-fun as shoveling our driveways and sidewalks. I clearly recall the morning three years ago when I called my husband, sobbing hysterically , after I’d spent over an hour trying to shovel my driveway clear while home alone with a two-year old. That was the year that we purchased a snow-blower. Slippery parking lots and sidewalks are a problem too, especially for elderly people who have trouble walking. To protect against slip and fall injuries, many businesses and homeowners heap generous quantities of salt onto the pavement to melt the ice. As much as we like to be safe, however, there is such a thing as too much salt.
Salt and other deicers work by lowering the melting temperature of ice so that it melts when the temperature is below freezing (32°F). However, traditional road salt (sodium chloride) doesn’t work when it’s colder than 15°F, so it is a waste of time and money to put down salt on very cold days. Other deicers such as magnesium chloride and calcium chloride work at colder temperatures (-10° and -20° respectively) but can be more expensive.
In addition, many homeowners and most businesses use way more salt than necessary. In reality, a relatively light dusting with about 3-inches of space between each granule of salt is enough to melt ice effectively without wasting salt. This translates into about 1 pound of salt (one heaping coffee mug full) for 250 square feet of pavement – a 20ft by 12.5 ft driveway or 10 sidewalk squares. Using more salt doesn’t melt the ice better; you just end up with more leftover salt sitting on the pavement. It’s important to note also that salt only works if you shovel your driveway and sidewalk first.
Using less salt this winter will help you to save money and protect our water resources. In the Twin Cities Metro alone, we use 349,000 tons of sodium chloride each year. Studies show that approximately 30 percent of the salt applied to the roads in the Twin Cities area ends up in the Mississippi River. The remaining 70 percent ends up in wetlands, lakes, soil, and groundwater. As a result, 30% of shallow monitoring wells in the metro have too high of levels of chloride, 39 metro-area lakes and streams are impaired by too much salt, and an additional 39 have almost surpassed health limits. This includes Carver Lake, Battle Creek Lake, Tanners Lake, Battle Creek, and Judicial Ditch 2/Sunrise River (impaired), as well as Perro Creek and Clearwater Creek (high risk of becoming impaired). There is currently no practical technology for removing salt from lakes, streams, groundwater and soil, so the only solution is to use less salt and hope that it doesn’t build up too quickly.
Enjoy warmer winter weather while it lasts and remember to take it easy on the salt this season!