Vermont's Winter Eco-Imperative: Hold the Salt
VERMONT -- Vermont is renowned for its eco-awareness. But for six months a year the state intentionally dumps a chemical into the environment that contaminates public waters, kills vegetation, injures wildlife, damages personal property, destroys vital infrastructure and harms human health. And we Vermonters just ride right over the problem.
We're talking road salt. Last year, the Vermont Agency of Transportation (AOT) spread more than 108,000 tons of sodium chloride on its roads and highways -- more than it did the year before but less than the annual average over five years. That number doesn't include the tons spread by municipalities, schools, private contractors and homeowners. Winter hasn't even officially begun, and already the AOT has used more than 15,000 tons of the stuff. Nationally, the use of road salt as a de-icer has been steadily climbing. In 1940, the United States used 164,000 tons of road salt. Last year, it used more than 16 million.
How healthy is Vermont's salty diet? For decades engineers have known about salt's tendency to penetrate concrete, and to corrode rebar, bridges and overpasses. But reliable, up-to-date statistics on the true cost of road salt are elusive. A report by the Transportation Research Board in 1991 estimated that repairing and replacing salt-damaged infrastructure nationwide cost from $3.5 billion to $7 billion per year. The automobile insurance industry doesn't even track the economic depreciation of rusting vehicles -- road salt plays such a crucial role in keeping accident rates low.
The impact of road salt on the environment has been more exhaustively studied. Besides harm to roadside trees, vegetation and soil, the biggest concern is its impact on drinking water. Two months ago, the National Academy of Sciences released a study which found that chloride concentrations in public drinking water from road salt are increasing at an alarming rate -- in winter, rivers and streams in parts of Maryland, New York and New Hampshire measure one-quarter the salinity of seawater. The report concludes that if road salting continues at its current rate, "many surface waters in the northeastern United States would not be potable for human consumption and would become toxic to freshwater life within the next century."
Oddly, the federal government doesn't regulate road salt or track its usage. But the justifications for its pervasiveness are obvious. Road salt is abundant and cheap -- about $44 per ton, compared to, say, $400 per ton for magnesium acetate, another chemical deicer. Rock salt is stable and easy to store and transport, and it does an effective job of retarding ice buildup by lowering the freezing point of water. Even factoring in environmental and infrastructure costs, many state DOTs have concluded that it's still the most cost-effective way to keep roadways clear in winter.
In Vermont, going salt-free simply isn't an option, for economic and public safety reasons, according to AOT's hazardous materials manager Mike Morissette. The department has experimented with alternatives, which proved less effective and more expensive. For years, state airports used a urea-based de-icer, since salt corrodes aircraft. But the urea was also harming groundwater and has since been discontinued.
On heavily traveled roads like the Winooski Bridge, "We're kind of caught between rock salt and a hard place," says Morissette. "If we put the salt down before a storm, it's all gone in five minutes. If we wait until the precipitation falls, with all that traffic and heated tires, it turns to ice immediately."
Interestingly, Montana, Colorado and other Rocky Mountain states don't use sodium chloride at all. Their snow tends to be colder and drier, making it less likely to form ice. Their roads are also made of different base materials, which react better to chemical deicers such as magnesium chloride and calcium magnesium acetate. Also, on mountainous switchbacks, rock salt is more likely to fly off the road and cause damage to vegetation and power lines below.
Morissette says that Vermont is working on ways to reduce its salt output. For example, it abandoned its "bare and wet" road policy, which required all state roads to be completely clear of snow -- a mandate which required enormous amounts of salt. Recently the AOT purchased tankers that spread a liquid brine instead of rock salt. Brine has several advantages, Morissette says. The oatmeal-like substance can be used in advance of a storm and in heavy traffic it doesn't bounce off roads, so the environmental impact is reduced. Brine can cut down salt usage by as much as a third. Morissette says the AOT plans to test it on I-89 between Montpelier and Burlington this winter. If it works well, they'll expand the practice statewide. And by the end of next winter, Vermont's cars may not all look like margarita glasses.