You're "pretty sure" the soil would be unsafe to grow food plants? I'd ratchet that up to "darned certain." I mean, if you apply poison to your garden where do you think it goes?
I'd either go the raised beds option, or replace a significant amount of dirt where you'd like to grow food crops.
Last edited by MassWineGuy; 06-24-2014 at 12:47 PM.