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The Environmental Costs of Road Salt

Putting rock salt on roads to keep them clear of ice and snow has become a mainstay of road management. The trouble is: After it’s used, it doesn’t disappear.

Plow Salting Road
Image source: Pixabay
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It’s hard to imagine a Northeastern winter without road salt. Since 1938, when New Hampshire first started experimenting with putting rock salt on roads to keep them clear of ice and snow, salt has become a mainstay of road management. The US currently uses roughly 20 million tons of road salt a year.

Salt works like a charm on frozen roads. The trouble is: After it’s used, it doesn’t disappear. Salt leaches into groundwater, runs into streams and collects in lakes and ponds. It builds up in the environment, so even if we use the same amount each year, the effects of salt on drinking water and ecosystems are increasing with every snowy winter that passes.

The center of expertise on how road salt affects our waterways isn’t a big Ivy League university. It’s a little research center in rural Dutchess County: the Cary Institute of Ecosystem Studies in Millbrook, where scientists have been tracking and measuring the ecological impact of road salt for years. Recently, the Institute published a sobering report on the topic: “Road Salt: The Problem, The Solution, and How to Get There,” a followup to another report they published in 2010.

The worst impacts of road salt on streams are felt by ecosystems. Communities of plants and animals in streams are more sensitive than most humans to small fluctuations in salt content. Even when concentrations of road salt in streams don’t rise high enough to kill stream wildlife, road salt can harm the ability of fish, amphibians and freshwater invertebrates to thrive and reproduce. A 2017 study by scientists at Yale and Rensselaer Polytechnic Institute found that frogs raised in pools laced with road salt developed skewed sex ratios, with more male tadpoles hatching than females. Over the long term, a shift towards more male frogs is likely to cause a decline in the population.  

Nationwide, road salt contamination poses an increasing threat to drinking water for humans. A 2009 study by the US Geological Survey found that two percent of wells nationwide had chloride levels above federal drinking water standards. In 2017, the Cary Institute released a study of 956 private drinking water wells in the Dutchess County town of East Fishkill. More than half of the wells had sodium levels above federal drinking water standards. In a region where private wells are common, and rarely tested, salinization of drinking water could become a public health problem even if public water supplies aren’t impacted.

Road salt played a large, if underappreciated, role in one of the most notorious public health tragedies of the past few years: the epidemic of lead poisoning in Flint, Michigan. In a recent feature in The Revelator, an online magazine published by the Center for Biological Diversity, Cary researcher Gene Likens explains the link:

When the city switched sources of water to the Flint River, the water had a much higher salinity because of runoff from road salts, which, without proper treatment, increased the corrosivity of the water. “That change in the chemistry of the water flowing through the pipes liberated lead from the pipes or lead-soldered connections,” explains Likens. Lead was the villain, but salt was its enabler.

Knowing the location of salt pollution hotspots can help municipalities prevent drinking water from becoming unfit for consumption. This map depicts chloride concentrations in East Fishkill, NY.  Areas in green had relatively low chloride concentrations, whereas orange to light pink areas had high chloride concentrations. Source: Kelly et al 2018, graphic used in a Cary Institute release.

Better Alternatives?

Alternatives to road salt exist, but none of them are perfect. One technique that has been shown to reduce the need for road salt is the application of salty brine. Salt dissolved in liquid doesn’t bounce off the surface of an icy road, and requires less salt to do the same job.

Brine can be made from regular road salt, but there’s also a free source—with a catch. For many small towns and villages in regions where hydraulic fracturing is producing large amounts of salty brine waste, using “fracking brine” in place of or in addition to road salt has proved a tempting solution. Using leftover brine from fracking wells can save a small municipality tens of thousands of dollars a year on expensive road salt. But fracking brine comes with another problem: radioactivity.

A study from Penn State researchers in 2018 found that brine used on roads in Pennsylvania towns had median radium levels of between 1,200 and 1,500 picocuries per liter, far surpassing the limit for industrial discharges of 60 picocuries per liter, and releasing more than four times as much radiation into the environment as wastewater treatment plants that handle oil and gas wastes.

Several years ago, with the debate over whether to allow hydraulic fracturing in New York State at a fever pitch, a movement to outlaw the use of fracking brine on roads succeeded in passing a ban on the practice in Ulster County. At least fourteen other New York State counties have adopted similar bans.

Other (and less literally and politically radioactive) options include molasses, beet juice, liquids left over from wine and beermaking, or brine from making cheese and pickles. But other methods come with different environmental problems, USA Today reports:

Russ Alger, director of the Institute of Snow Research at Michigan Technological University, says some of the alternatives to salt there also pose environmental concerns. Beet juice, for example, may deplete oxygen in waterways.

“When you look at all the options, a lot of time road salt turns out to be pretty good,” Alger says. “So we keep coming back to road salt. Cost-wise, efficiency-wise, availability-wise, it’s just the best answer. I don’t see it getting replaced for a long, long time, if ever.”

The best option, according to Cary researchers, is to be smarter and more strategic about the use of road salt. When forecasts are predictable, trucks can spray brine before snow and ice falls, which requires less salt for the same effect. Another is outfitting trucks with applicator regulators, so the precise amount of salt needed can be measured and used.

Developing a road salt management plan, and keeping careful records about how roads are managed, can help local municipalities cut down on salt use, sparing the environment and lean budgets at the same time. According to the Cary Institute, the Dutchess County town of East Fishkill saved $242,810 in the first year after outfitting their trucks with application regulators in 2009—a financial win for the town, even after spending $140,000 on the new equipment.

When environmental problems have a single, obvious source—like GE dumping PCBs in the Hudson River—it’s easy to find a villain to blame. Complex problems like road salt contamination are more nuanced, and solving them often forces communities to weigh competing priorities and develop new expertise.

Problems with nuance and depth also deserve careful, thorough reporting: the kind of reporting we’re building a local newsroom to deliver.