Rock salt means safer roads, but it can also wreak havoc on the environment, leaving public works officials across the state trying to reduce salt use while preserving safe road surfaces.
Salt’s advantages are obvious. It is cheap, natural, easy to apply and effective. Still, with concerns about the impact on the environment, human health, road infrastructure and vehicles, those who plow the roads are always seeking ways to use less salt.
A survey of area towns and cities shows dramatic differences in the amount of rock salt used on local roads, with Fairfield using more than three times the rock salt per mile than Farmington.
With roughly a billion pounds of rock salt spread on Maine’s roads every year, the consequences for the environment, human health, public infrastructure and vehicles are significant.
“It doesn’t disappear,” said Sarah Flanagan, who published a study on ground water quality in New England for the U.S. Geological Survey earlier this year. “It has to go somewhere.”
Salt can change the living conditions in the local watershed by increasing the salinity of lakes, streams and vernal pools, killing or weaken native species like white pines, salamanders, frogs and fish while encouraging more salt-tolerant invasive species, like phragmites, a hardy European reed.
Groundwater contaminated by rock salt is a human health hazard in the form of unwanted sodium.
And, as many vehicle owners are aware, salt’s corrosive influence can shorten the life of a vehicle and lead to costly repairs. The total value of vehicle damage is not known, but the cost of corrosion on public roads and bridges is an estimated $16 billion to 19 billion per year.
During the past 10 years, as awareness has grown about the negative impact, technology and practices have emerged to minimize the amount of salt needed on the road.
A salty state
The state Department of Transportation treats 8,350 miles of road during about 30 storms per year. Depending on the storm conditions, anywhere from 20 to 800 pounds of salt can be used per two-lane mile per storm.
Roads in the Northeast get more road salt than in any other region in the country. Maine has 23,450 miles of public roads, more per person than any other state in New England, so the emerging issue of salting the state’s environment is particularly important.
A 2010 University of Maine Study showed that 490,000 tons, or about one billion pounds, of rock salt was bought statewide in 2008 — four times the total weight of the state’s 1.3 million residents.
Nationwide, studies estimate that about 23 million tons of salt are applied to paved areas every year.
A study in New Hampshire found that private roads and parking lots accounted for about half of all road salt, while municipalities accounted for 30-35 percent. The state was responsible for the rest.
Some towns saltier than others
The amount of rock salt that communities throughout central Maine use on their roads varies widely.
Most used between five and seven tons per lane mile, but Augusta used eight tons and Fairfield 10. At the other end is Farmington, which used just 3.26 tons.
Farmington Public Works Director Denis Castonguay said the town has been making progress in leaps and bounds by participating in education programs offered by the state and the University of Maine.
“Our operators are just getting more and more aware,” he said.
Last year, he said, the town used 784 tons, far less than the 2,000 used annually just six or seven years ago.
Castonguay couldn’t point to a single factor to explain the improvement.
“It’s the little things,” he said. “We monitor the storms real close. We also monitor the road temperatures, and we start early.”
Unlike in many towns, Castonguay has a laser-based temperature sensor in his truck that he uses to read the road temperature, an important data point that can make salting more efficient.
Still, he said, he sees room for improvement.
“We’re about 10 years behind the technology that’s out there,” he said.
Fairfield Public Works Director Bruce Williams said he isn’t sure why his town uses more salt than others in the area. Town Manager Josh Reny pointed out that the town has no salt-priority roads, which are treated exclusively with salt, instead of a sand and salt mixture.
It seems obvious that roads requiring only salt would get the most, but Castonguay said the opposite is true. During a storm, he said a salt-priority road that has been pretreated with a relatively small amount of salt will melt snow as it lands. When plows revisit a stretch of road multiple times during a storm while spreading a sand and salt mix, it creates layers of icy grit on the road that then has to be melted with more salt at the end of the storm.
The Department of Environmental Protection is hosting two workshops this month to help plow operators and others who are responsible for snow removal to manage salt more efficiently. Spokeswoman Samantha Depoy-Warren asked that those who are interested in learning more about the sessions, scheduled for Portland on Nov. 20 and Augusta on Nov. 27, call 215-9237.
Brian Burne, highway maintenance engineer for the Maine Department of Transportation, said strategy to reduce salt continues to evolve.
“It’s a big change from the days when we would drive around and throw sand out the back,” he said.
The state’s plow trucks, and most trucks in most towns, are equipped with computer control systems that spread salt optimally for factors like truck speed, air temperature and storm condition.
In Farmington, Castonguay said, the systems, which cost a few thousand dollars apiece, pay for themselves in a single winter by reducing salt cost. Data from infrared temperature sensors mounted on the side of plow truck mirrors is fed into the computer system for more efficient plowing.
Some alternative substances are inexpensive but unproven or are associated with different environmental concerns. Others work only during a fairly narrow range of storm conditions. And others are consistently effective but cost too much.
According to Burne, one alternative, calcium magnesium acetate, is about 15 times more expensive than road salt.
“If we switched entirely over to that, it would eat up our entire budget so we couldn’t pay for people or equipment,” he said.
One product that has gotten a lot of attention recently is Ice B’Gone, a beet sugar based additive that gums up rock crystals, preventing them from bouncing off the road and into a ditch without melting any ice. The liquid, which has been endorsed by the federal Environmental Protection Agency, also helps the salt to be effective at lower temperatures.
Many public works directors are taking a wait-and-see approach to the relatively new product but it is in use by the state transportation department and in Skowhegan, where Road Commissioner Greg Dore said it has helped to reduce the amount of salt used by about half.
Burne said even more advanced equipment remains beyond the reach of the state. One example is flexible rubber-treated carbide blades that will mold to the contours of the pavement, which leave less snow behind to be melted. Another is a GPS system that automatically adjusts the amount of salt being spread using real-time information such as the vehicle location, traffic flow and weather systems.
All of the public works directors agreed that there’s another obstacle to reducing salt: changing public expectations.
They said it wasn’t that long ago that roads would go unplowed for days after a storm and people traveled at their own peril.
The directors said more people now expect to be able to drive fast during and after a snowstorm, which requires more resources, including more salt.
Matt Hongoltz-Hetling — 861-9287