The HF monster everyone is talking about in this thread is dangerous only as a concentrated acid. It's highly soluble -- reduce it with a rainstorm or two and let it recombine to a neutral pH and you rapidly get to (literally!) toothpaste-level toxicity.

There's a VERY serious discussion to be had about the safety for a backyard chip fabricator. But the idea that this is some kind of long term pollutant (relative to much more serious issues like the cleaning solutions in your very own closet!) is pretty spun.

Edit: yeah, as the responses point out, the "superfund" sites in question are things like VOC contamination you see with any urban industry, nothing particular to semiconductor fabrication that would justify the upthread quote about contamination "for many generations to come".