Not as worried about the bottom as much as where to keep the tractor. No need for it to find the bottom.
Sounds like this is maybe what you have discovered. A sinkhole that was back filled with "not so clean fill".
Yup...posted before I got to the end of the thread Caught the phone line too eh? Could have been worse. Not near as costly as this screw up with fiber optic....
You know something, that is entirely more accurate! 7 out of 8 really do know!!! You're on your game tonight, sir!