Hey
@Frillylily,
I don't claim to know everything or understand whatever you have got going on there--
but...
at the farm, I had a septic tank and a drain field that went who knows where and mature trees everywhere. The system failed, badly. New tank and new system installed to pump out to a long, narrow mound for drainage about 300 feet away from the tank and way on the other side of the edible garden along a grove of trees on the down-hill edge of the property. The mound discharge worked well --above the tree roots--and the trees drank up everything that didn't evaporate. The biggest problem was keeping saplings out of the mound, but I grew all sorts of shallow rooted flowering stuff on it. (It has since been converted back to grass so that it can be mowed periodically because there is no one to 'weed' the volunteer trees)
Soil testing revealed that the main problem I had was with organic and inorganic toxins rather than pathogenic bacteria.
Besides the septic failure, probably a result of the fact that it was customary in that area to bury garbage and all manner of junk or just pile it up randomly and leave it everywhere
and as Rick said, much of that stuff lingers on and on...
Plants are much more capable of incorporating organic and inorganic toxins than bacteria anyway, so that was my primary concern with the edible plants and location of the edible garden.
No doubt it would be expensive to convert your septic system to one that recycles treated water or one that drains differently, but it could be that with limited space in which to garden, conversion might be one of the most worthwhile investments long term. Something to consider anyway, but first you probably ought to figure out how and where it drains and what issues, if any, you have as a result.
The vertical axis is still very much an option, regardless. (I grew veggies and herbs in a discarded bathtub when I lived in a trailer)
Personally, I don't think a few raised beds over some areas of the potential drain field would compromise the drainage ... but, then again, I don't know how your place drains???
