Here is a picture looking down into the septic tank, what this shows is the remanents of the old lid and the dirt that was sitting on top of it. The replacement of this lid is a dirty and nasty job and should only be performed by properly trained and equipped persons. KountyWide Septic has the equipment and experience.
New lid installed and ready for backfill. Morale of the story: Be careful where you drive your tractor;)