Road salt isn’t meant to melt all the ice and snow but to detach them from the road, creating slush instead of a slick sheet. Hundreds of trucks spread salt in and around Milwaukee during the winter, and repeat applications are often needed.
Despite efforts to replace salt with cheese brine or other agents, the city stockpiled some 57,000 tons of rock salt and 24,000 gallons of salt brine for the winter of 2017-18. In a survey of 22 states, Wisconsin was the fourth-heaviest user of road salt, behind New York, Ohio and Indiana. All that salt has to go somewhere, and it’s wherever runoff takes it.
In 2010 researchers tested water from 12 Milwaukee streams during February and March and found that salt had turned seven of them toxic to their plant and aquatic life. The salt levels drop during warmer months but have increased, overall, since 2010.
Even the salinity of Lake Michigan has begun to creep up, and while the impact on the big lake will probably remain low for years to come, local governments are on the hunt for a kinder, gentler replacement for road salt.