The tank. I think he say it was about 6-8’ in the ground. Not sure how deep the clay is
6 to 8 inches?
or what you wrote...
6 to 8 feet?
6 to 8 inches depends on the type and size of the of tank.
6 to 8 feet... mostly unheard of but you could drive anything over that.
I have a 1250 gallon drive over tank, reinforced tank.
My tank is 3 feet in the ground and the leach (drain field) is about 2 to 3 foot underground.
Never have an issue with working over that.
If the tank and leach field are 6 to 8 inches, I wouldn't put any equipment on it ever.
Your very liable to do some hidden damage to some part of the system.
Personal advice I would stay off of it.
Business advice STAY OFF OF IT, unless you can get it in writing from the septic installer that you won't do damage to it, and that any damage that happens is covered by them at their expense.