http://seattletimes.nwsource.com/htm...leanup23m.html
Here's one article from a Seattle paper which mentions why salt and sand are not their first choice, but doesn't go into much detail. One reason why Seattle wouldn't use the chemicals is more about geography than about tree-hugging. All of that runs into the sewers and directly into Puget Sound. Granted stuff used on the east side can run into the Columbia and the Snake, and eventually out to the Pacific. It is also much more humid on the west side due to the rain forest and the proximity to the Ocean. It is much drier over here, which can help, and it stays colder longer (though it is raining and melting now, ugh, so it can refreeze snow on top of ice).
This article
http://seattlepi.nwsource.com/local/...lackice20.html discusses other alternative deicing such as waste water from cheese making. I'd also not like salt as the underneath of my car has corrosion, which didn't happen from my town, but from previous winters in Alaska before I bought it and from traveling in other states.