Jeremy Smith climbed into the cab of a front-end loader last week and maneuvered it to lift several hundred pounds of coarse rock salt.

It was the day after the first lowland snowfall of the season, and Smith, a maintenance supervisor at the Vermont Agency of Transportation, wanted to make sure road crews were ready for the approaching winter.

But instead of dumping the gray crystals of sodium chloride into the bed of one of the orange snowplow trucks parked at the agency's Colchester outpost, Smith drove his load into a cavernous wooden shed and to a large metal hopper. He positioned the bucket over the machine's wide mouth and poured the salt inside. As he did, powerful jets of water sprayed the granules, dissolving them into a brine ready to be added to the 30,000 gallons already stored in towering tanks nearby.

That solution is a key component of the state's effort to reduce the amount of salt it spreads every winter. Road salt, a less processed version of table salt, works wonders to keep roads clear in winter by lowering the freezing point of water. But it also gets washed into streams and lakes, where it increases salinity and can harm fish and other aquatic critters.

"Salt is a pollutant, but it's a necessary evil," Smith said.

State-of-the-art plows spray salt brine, also called liquid salt, on top of dry road salt in a two-part process to make winter road travel safer. That allows crews to use less salt, reducing the environmental impact, Smith said. The state has been using this technique since 2008.

Despite the state's efforts, however, salt levels in waterways are on the rise, in part because most individual town road crews still treat icy roads the old-fashioned way. That compounds the water-quality challenges from pollutants such as phosphorus, said Tim Clear, a watershed manager at the Department of Environmental Conservation.

"When you start combining these stressors, it has a combined effect on things that live in these streams," Clear said.

Scientists agree: A recent article in the online journal Nature Reviews Earth & Environment concluded that increased salt use threatens to cause "serious or irreversible damage across Earth systems."

The United States uses 21.5 million tons of salt a year to keep roadways clear, much of it in the Northeast. The environmental impact of salt on waterways has been well known for years. In New York, the Lake George Association has one of the nation's most aggressive salt reduction campaigns, calling road salt "the acid rain of our time." Researchers have documented that salt levels in Lake George have tripled since 1980, creating potentially toxic conditions for wildlife.

Use of road salt contaminated the drinking water supply in Merrimack, N.H., forcing the local water district to stop using one of its wells. In response, the state launched a Green SnowPro program to educate private plowing contractors about the best salt application practices.

In Vermont, programs such as the University of Vermont's Lake Champlain Sea Grant hold annual workshops aimed at educating road crews and the public about the persistent problem.

That outreach hasn't yet made a measurable difference. Many communities and private property owners, including those with large parking lots, continue to use the mineral liberally.

"The goal, obviously, would be to use less salt, but it's a balancing act between safety and impacts to the environment," Clear said.

Runoff from agriculture, as well as water softeners used in residential wells, contribute to the rising salt levels in waterways, but road salt is the "overwhelming source of the problem," he said. Salts and other "chemical cocktails" that they create build up in soil, surface water and groundwater and are difficult to remove, according to the U.S. Environmental Protection Agency.

It's the chloride in road salt that is most problematic for the health of aquatic life. In 2022, seven streams in Vermont were considered impaired by high chloride concentrations, according to environmental regulators. Several of the waterways, including Potash Brook in South Burlington, flow through areas with some of the densest commercial and residential development. Another three streams will likely be added to the list in 2024.

Additionally, three waterways — the Upper and Lower Winooski reservoirs and Kettle Pond in Brattleboro — have been found to have average chloride concentrations greater than 230 micrograms per liter, the level that signals a chronic problem.

Clear said research has shown that lake zooplankton, microscopic animals that are an important part of the aquatic food chain, can be harmed by chloride levels as low as 50 micrograms per liter.

Chloride in Lake Champlain is well below that level — ranging from about eight to 16 micrograms per liter — but the concentration has been rising in the past decade.

The same is true for major rivers such as the Winooski, Lamoille and Missisquoi. The amount of chloride in the Winooski has increased the most, and fastest, with more than 25 micrograms per liter found in 2022.

"I think the ... trend is of concern," Clear said.

The Agency of Transportation is doing its part. By far the state's largest road-clearing operation, with 275 plows responsible for 3,300 miles of roadway, it has reduced use of salt significantly in recent years.

In 2022, the agency used 125,000 tons of dry salt and 1.4 million gallons of brine, both well below the five-year average. The 2,120 tons of sand it used in 2022 was also 32 percent lower than the previous year.

Milder winters are responsible for some of the drop, Smith said. But the expanded use of salt brine has also contributed significantly.

Several years ago, the state's garage in Colchester was the only one with brine-mixing capacity. Now seven VTrans garages have the equipment. Most of the state's fleet of snowplows carry brine in tanks holding up to 1,200 gallons. They spray the brew onto rock salt before it's spread on roads, Smith explained.

This "pre-wetting" activates the salt so it starts having a de-icing effect as soon as it hits the road. It also keeps more of the salt on the road by reducing the amount that scatters into ditches. Adding the brine to the dry salt creates a slurry that is the consistency of oatmeal, Smith said.

Crews used to apply brine directly to roads in advance of big storms to make clearing snow easier, but public concerns about corrosion to vehicles caused the state to abandon the practice, Smith said.

The salt solution works well down to about 15 degrees. Below that, the agency can use chemical additives such as magnesium chloride to prevent ice from forming, but that's rarely been employed in recent years, Smith said.

Following the state's example is not so easy for small cities and towns. The equipment needed to mix batches of brine costs about $100,000, said Mark French, the road foreman for Hyde Park, which obtained the necessary equipment to use liquid salt three years ago. While that is cost-prohibitive for smaller towns on tight budgets, it saves money in the long run by reducing the amount of salt the town needs to buy, he said.

French estimates that he's been able to cut salt use in Hyde Park by 40 percent in recent years, in part through the pre-wetting technique. Other helpful technologies include computerized salters that adjust the rate of salt spreading to match the speed of the plow. Ground temperature sensors on his five plows also let the drivers see when the road temperature is warm enough that no salt is needed, he said.

Kris Stepenuck, an associate professor at the University of Vermont's Rubenstein School of Environment and Natural Resources, said some Chittenden County cities have expressed interest in replicating what Hyde Park has done. But overall, according to surveys she's conducted, most communities are still not using best practices to reduce salt use.

"The message to me is, we have work to do to get different municipalities on board," she said.

According to a survey Stepenuck conducted in the Lake Champlain basin, Vermont cities and towns were hesitant to switch to lower salt methods due to concerns over liability and expenses.

But with salt costing $91 a ton this year compared to $71 just last year, reducing salt use isn't just good for the environment, it's good for the bottom line, French said.

"It's an investment that will definitely pay you back in a hurry," French said.