The city of Seattle doesn't put salt to clear roads covered by snow because they don't want the salt to run off into Puget Sound according to this article:

http://thesecretsofvancouver.com/wordpress/saltless-in-seattle/environment

I don't know much about the salt content of the water in Puget Sound, but it is hard to believe that salty water run-off from roads in the city on the rare occasions when it snows there would make much difference. Not clearing the roads leads to inconvenience for the public, and more auto accidents. This seems to be another instance where environmental absolutists are unwilling to do a cost-benefit analysis.