herongrrrl
Here’s King County’s website about this:
http://www.kingcounty.gov/healthservices/health/ehs/toxic/TacomaSmelterPlume/background.aspx
I’ve done a bunch of research on this because I was concerned for my own garden. The key thing to remember is that arsenic “dilutes” in soil very quickly and easily when the soil is disturbed. Unless the soil where you’re planning to make your garden hasn’t been disturbed at all in the last 50 years or so, your soil is probably fine. The places of most concern are in Tacoma and on Vashon/Maury. Friend of mine who live on Maury built raised beds and brought in clean soil, and don’t grow any root vegetables as precautions.
What I haven’t been able to find out is whether or not some plants absorb more arsenic or other impurities from the soil than others. If anyone knows where to find that, I would love to know!