Even in a winter like this, with seemingly endless snow, cities are discovering the benefits of putting a pinch on the salt that makes roads safe.
The South Washington County Watershed District, which manages numerous water quality projects in eight cities, is focusing new efforts on helping cities manage how they apply salt to roadways.
It's good for the environment and the bottom line, said Matt Moore, administrator of the watershed district.
"It's a win-win -- there's less chloride use and less environmental impact," he said. "But what's not going to go away is the need to balance that against safety."
In 2009, the watershed district awarded Cottage Grove a $50,000 cost-share grant to retrofit its fleet of snowplows with new technology that takes the guesswork out of applying road salt.
It uses GPS technology that regulates truck speed and an infrared system to gauge road temperature to automatically and precisely regulate how much salt is dispersed.
It's proven so successful, he said, that other cities are likely to pursue the technology.
A second project under consideration is a road salt storage facility in St. Paul Park. The district would fund half the building's $80,000 cost.
The upgrade will better prevent runoff of chlorides, Moore said.
Calcium chloride is the most common salt used to clear roads in winter, because it's more effective at melting ice at lower temperatures than sodium chloride, the chemical equivalent of table salt. It's also less harmful to the environment than the salt found in shakers, but still has potentially damaging effects.
Chloride can only be removed from water by reverse osmosis, and it doesn't break down but moves along with water. That means it keeps building up in the environment.
In high concentrations, it can kill fish and other aquatic species. At chronic, lower levels, it can impair lakes, streams and other waters, according to the Minnesota Pollution Control Agency. Studies also have linked salt to bird deaths and suggest that some amphibian species like frogs are sensitive to high levels of road salt. It also hurts plants and makes soil more prone to erosion.
The first winter of the retrofitted plows in Cottage Grove brought a significant reduction in salt use, said Jennifer Levitt, city engineer. "The key thing is that it applies the correct amount of salt for the temperature and road conditions."
The technology is better able to adjust to all the variables that go into plowing and efficiently salting roadways: Truck speed, the rate at which salt comes out of the box and how wide a swath is being covered.
The computers now do those calculations, Levitt said. The infrared sensors even gauge the road temperature, so that when plows come to a colder bridge deck or shady spot, they will increase the salt being spread. This system even eliminates the problem of piling of salt at intersections.
Besides saving money and helping the environment, she said, the new system has virtually eliminated the need for spreading sand along with the salt. That also spares the environment and saves the city money, because in spring the sand must be swept from streets and removed from sewer pipes and ponds to keep sediment from building up.
Jim Anderson • 651-735-0999