I have messed up 2 septic systems.
1) guy told me it was ok to back over lawn to deliver 2 yards of soil with my pickup truck. WHAM! rear drivers side tire through the top.
2) doin a clearing / lawn extension job. had a 9K lb excavator there pullin stumps and moving vines around. Guy told me that the septic system was way over there and I didn't have to worry. Start diggin this one descent size cherry stump, start hittin these rocks, then I start to smell something, then I start to see a fluid coming out of the ground. Not my fault so I just burried it and told the customer.
3?) drove over a customer's leach fields to pull some trees over and got my ear chewed off for that. No damage as far as I know though.