Getting road salt down to a science

27 Feb 2022 12:21 PM | Smart About Salt (Administrator)

Valley News - Getting road salt down to a science (

CLAREMONT — The Claremont public works department has technology on its four newest trucks that calibrates salt distribution to road temperatures and air temperatures. Drivers prescribe just enough salt to keep the roads safe, and no more.

“We were using 350 pounds per lane mile; now it’s a little under 200 per lane mile,” said Ted Wadleigh, the city’s assistant director of public works. “We cut it by half.”

Reducing deicing salt is an important environmental goal. The salinity of freshwater ecosystems is climbing across the world as salt from fertilizers, mines and deicing highways washes into ponds, lakes and rivers. Salt concentrations far below the Environmental Protection Agency’s threshold still cause significant environmental damage in lakes and ponds, according to a new international study that Dartmouth contributed to.

The researchers concluded that there is an “immediate need to reassess current governmental thresholds to protect lakes from salinization.”

The EPA threshold for salt contamination is 230 milligrams of chloride per liter, while Canada’s is only 120 milligrams of chloride per liter. (Chloride is one of the two chemical components in rock salt). Even at Canada’s lower limit, researchers saw massive declines in zooplankton.

The Dartmouth researchers gathered water samples from Storrs Pond, Mascoma Lake, Boston Lot Lake and Goose Pond to recreate lake ecosystems in trash cans buried on the Dartmouth Organic Farm. They inched up the salt concentrations in the “mesocosms” each week. It only took days for zooplankton to suffer from high salt levels, said Jennifer Brentup, a former postdoctoral fellow at Dartmouth who conducted research for the study.

Zooplankton are crustaceans so small that they are hard to see with the naked eye. But they are a critical hub in the traffic network of lake ecosystems, said Kathryn Cottingham, a professor of biological sciences who led Dartmouth’s research team. Fish eat the zooplankton, and the zooplankton eat phytoplankton, also known as microalgae. The zooplankton are at center of the food chain, passing energy that the phytoplankton capture from the sun up the food chain. Without them, the more recognizable inhabitants of our lakes and rivers, such as trout and salmon, cannot survive.

“Basically, if you break the traffic network, then everything further up will fall apart,” Cottingham said.

As salt levels rise, negative impacts cascade through the ecosystem. Phytoplankton populations rose in nearly half of the study sites. In some sites, they formed a mat on the surface of the water, blocking light. Fish hunt by sight, and so they go hungry in the dark. The rapidly reproducing phytoplankton consume the oxygen, stifling fish.

The Dartmouth researchers said that lakes and ponds close to roads are most at risk. In 2021, the U.S. Geological Survey estimates that the U.S. consumed 54,000,000 metric tons of salt, and approximately 42% was used for highway deicing. Deicing salt damages more than the natural environment. It also seeps into groundwater, contaminating drinking water with a salty flavor and harming people with high blood pressure. Salt corrodes cars and infrastructure. The EPA estimates that the U.S. spends $5 billion dollars on annual repairs because of rock salt.

Climate change puts upward pressure on the amount of deicing salt New England needs to keep its highways safe. In New England, Brentup said that climate change is bringing more extreme winter precipitation and temperature swings. Rapid freeze-thaw cycles mean more ice on roads, and more salt.

Lakes and ponds in the region are suffering, and the problem is escalating each year. In 2008, New Hampshire listed 19 chloride-impaired water bodies that passed the EPA’s threshold. By 2020, that number climbed to 50.

“The chloride concentrations in New Hampshire’s lakes have been creeping steadily upwards since late ’80s and early ’90s,” Cottingham said. “Especially with interactions with global warming, we could be hitting thresholds that could cause big changes fast. How can we slow those things down?”

Cottingham emphasized that what we do on land affects our water. The New Hampshire Department of Environmental Services warns that neither evaporation nor chemical breakdown nor plants remove any significant amount of chloride from the environment. The salt we spread on our roads and sidewalks will almost all eventually end up in our water. The department emphasized that the only way to prevent more contamination is to limit how much salt we put down, without compromising safety.

New Hampshire has led a road salt reduction program that trains snow and ice management professionals to use as little deicing salt as possible. As of November 2020, the EPA credits the program with reducing road salt use by 20%.

Brentup listed off many ways we could reduce our dependence on deicing salt. Porous pavement absorbs the water that would otherwise freeze into a treacherous sheet of ice. “Brining” roads with a salt-water solution before a snow event requires much less salt than spreading rock salt. And some road crews are using biodegradable substances such as beet and pickle juice to slow ice formation and make the salt solution stick to roads rather than wash off.

Last year, the Claremont Public Works Department tried magnesium chloride mixed with molasses. The molasses limits rust on vehicles and sticks to the roads, reducing how much magnesium chloride the department’s trucks spread, Wadleigh explained. But magnesium chloride works only when temperatures stay far below freezing. In a warmer winter, it turns slick, reproducing the dangers of the ice it is supposed to limit. Over time, Wadleigh said, the department will update all its vehicles with new technology that distributes salt more efficiently.

On average, over the last two winters, Claremont spent $168,426 to buy 2,700 tons of salt. This year, salt prices are up, but the city needs much less than it used to.

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