Any sort of construction, etc. needs to have the machines avoid the drain field. I wouldn't drive over one. Something small like a skidder, maybe, if there were a plywood path to distribute the weight.
That said, newer fields are PVC, not clay pipes. At any rate I wouldn't want to compact it at all.
That said, newer fields are PVC, not clay pipes. At any rate I wouldn't want to compact it at all.