An unexpected freezing rainstorm that began during the afternoon of New Year’s Eve left many local residents scrambling to rethink their holiday plans.
The weather event took many by surprise — including the city of Asheville. The National Weather Service did not predict the precipitation, so there was no indication that the city should pretreat the roads, says city communications specialist Polly McDaniel.
“Once the ice event began to occur, all Public Works Streets Division employees were deployed for around-the-clock shifts,” she says. “Those are 12-hour shifts, one in the day, one in the night.”
In response to the treacherous road conditions, public works employees turned to a reliable tool, one they’ve used countless times to reduce the hazards of ice on city streets: road salt.
Salt lowers the freezing temperature of water, halting the production of ice and ensuring that roads don’t turn into Slip ‘N Slides for motorists. But excess salt can travel into nearby waterways and soil, impacting the health of the environment.
“At high levels, salt is directly toxic to some aquatic wildlife such as fish, amphibians, invertebrates and plants,” says Ann Marie Traylor, executive director of the Environmental Quality Institute, a nonprofit environmental research laboratory based out of Black Mountain. “Lower levels can degrade aquatic wildlife’s health and survival more slowly. Salty runoff can also kill roadside grass and trees, which can lead to erosion.”
Salting the Earth
In each of the past two fiscal years, Asheville has used a little less than 1,300 tons of salt on city streets for snow and ice removal, says Greg Shuler, the city’s director of public works. Asheville maintains 409 miles of paved roads and partners with the N.C. Department of Transportation to treat an additional 91 miles of state-maintained roadways that fall within city limits.
Over the past four years, the NCDOT has used an average of 115,000 tons of salt annually. In Buncombe County specifically, NCDOT uses about 5,000 tons each year. “We utilize as little salt as possible not only to minimize cost but to reduce any potential environmental impacts,” says Mark Gibbs, a maintenance engineer for NCDOT who is based in Asheville.
He says NCDOT calibrates its trucks each year to place salt at a specific rate on highways. Along with the use of salt and sand mixtures, these measures minimize salt application. In Asheville, the Public Works Department sweeps nearly 4,000 miles of street each year to remove salt and debris.
“This sweeping occurs every day and night during the week — weather permitting — to assure timely and thorough removal of salt and other contaminants from reaching our creeks and rivers,” says Shuler.
A salt industry advocate argues that road salt has only a transient impact on the environment. Wilfrid Nixon is a scientist at the Salt Institute, a nonprofit trade association.
“Like all tools that we use, there are pluses and minuses,” Nixon says. “When you put a material out into the environment, it remains in that environment until it is either broken down or it washes away. With road salt, it doesn’t break down. The sodium or the chloride, they don’t go into different forms. They stay there and they will eventually get flushed out of the environment by rain, going into rivers, going down streams back to the ocean, which is ultimately where all the salt came from.”
Wherever it eventually ends up, some salt does find its way into nearby bodies of water. The Environmental Quality Institute operates a monitoring program that tests water on a monthly basis at fixed locations in Western North Carolina. One of the measurements the monitors pick up is conductivity, which measures the electrical conductance of the water.
“Conductivity is higher when salt is present, so it’s a good indirect test,” says Traylor. “We usually see a rise in conductivity after winter weather events, especially after melting and rainfall on primary roads.”
As an example, Traylor says the conductivity reading last January was extremely high at a monitoring site in Ross Creek near Tunnel Road, a body of water that receives runoff from Tunnel Road and Interstate 240.
“For perspective, only two samples from Buncombe County have exceeded this level since our monitoring began in 1990,” Traylor says. “We were able to alert our local government officials and watershed planners, so they could coordinate and be on the lookout for a solution.”
The best option
Alternatives to road salt come in several forms. Some municipalities have even used a mixture of salt and beet juice to treat roads but for local agencies, salt still tends to be the best available option.
Shuler says Asheville has considered alternative de-icing methods, but none appear to be as effective as road salt. “We continue to monitor how advancements in the industry progress and keep our options open to deliver the best results for the city to recover from snow and ice events,” says Shuler.
NCDOT, meanwhile, will sometimes use salt brine before a storm, which reduces the overall usage of salt. The city has used this method, but Shuler says it’s only effective for weather events that aren’t preceded by rain, which can simply wash away the brine.
NCDOT also uses a compound called calcium chloride in extremely cold conditions — 15 degrees or less — but Gibbs says the department limits the use of the product and others because of its cost.
“The bottom line is that salt is the most cost-effective treatment with minimal to no impacts to the environment provided it is utilized properly and at the correct rates,” says Gibbs.