I was wondering if anyone has any knowledge on soil health in San Francisco. I live in the outer Richmond neighborhood (94121) and just got my farmbot in the mail. I want to build a raised bed and add at least a few inches of dirt. But, I’m worried I really should add 18 inches and put a barrier to prevent my plants from connecting with the natural soil. I live pretty high up on a hill and I’m pretty sure there has only been homes on this plot of land for all of time. Any advice?