The Minnesota Department of Transportation is falling behind on its goal to use more liquid brine on roads, an effort designed to reduce the annual blankets of salt that make streets safer but can kill lakes and rivers.

Salting roads, sidewalks and driveways clears snow and ice, but the runoff also pollutes waterways with chloride, which are nearly impossible to remove. According to the Minnesota Pollution Control Agency, one teaspoon of salt can permanently contaminate five gallons of water.

That's part of why MNDOT is aiming to use 200 gallons of liquid brine for every ton of road salts it spreads by 2027. The ratio has been improving, but the agency only managed to use 54 gallons per ton across the state in 2023, according to a December report to the Legislature. At that rate, it wouldn't even be halfway to the benchmark in 2027.

Yet, Jed Falgren, the state maintenance engineer for MNDOT, is optimistic about the state's progress. The ratio has gone up consistently for the past four winters.

"What I'm most concerned about is the direction," Falgren said. "It takes some time to get this to move."

The state uses brine by itself, where it can be effective in clearing thin layers of ice, like the freezing fog that made some roadways slick across Minnesota this week. It also sprays a mix of brine with solid salt on icy or snowy roads.

Mixing the liquids and solids makes it less likely that rock salt will bounce off the road. It's also more effective: In testing conducted at Minnesota National Guard's Camp Ripley, the agency found that mixing 100 gallons of brine into each ton of salt required 30% less salt overall and melted ice 30% faster, Falgren said.

But using more brine means first fitting salt trucks with brine tanks and then making sure DOT has the equipment to mix the solution. Falgren said he had hoped to get $9 million in state funding for each of the next four years to build out that infrastructure, but was instead granted $4 million for 2024 and the same amount in 2025.

Another challenge is that it's counter-intuitive to spread liquid on a road in freezing conditions, and not everybody is on board with the idea. The brine MNDOT uses is about 23% salt, and just like rock salt, it lowers the freezing point to help clear ice and snow.

"We have to convince ourselves," Falgren said. "We have to convince our employees."

Salt pollution is the worst in the Twin Cities, which has multiple impaired streams, lakes and wetlands, according to MPCA. It's also the part of the state with the worst liquid-to-solid salt ratio: it used just 28 gallons of brine per ton of salt last winter, according to MNDOT.

The region sees its share of dangerous road conditions and car collisions every winter, and as a result, "they look with a skeptical eye at some of this stuff we're presenting," Falgren said.

While the state keeps updating its salting strategies, this relatively warm and dry weather has offered a reprieve. Falgren said that as of Tuesday, MNDOT has used just over 65,000 tons of solid salt. At the same point last year, trucks had already spread 163,000 tons.