300 pounds of road salt is applied per lane per mile. It sounds like a lot! That is the industry standard! Certainly less is applied if conditions require it, but it takes many factors to determine the correct treatment to keep roadways safe in the winter months.
According to to Wisconsin Saltwise, an organization designed to educate Dane County residents and maintenance professionals about road salt safety, it takes one teaspoon of salt to permanently pollute five gallons of water to a level that is toxic for freshwater ecosystems.
An average of 500 tons of salt a year is put into Lake Mendota during an average winter. Not intentionally of course, but the salt can wash into the lakes when met with rain.
Not only does salt degrade lake ecosystems, but it also diminishes the quality of drinking water.