Makes me want to start digging mine out .... but I'd be too tempted to leave it all dirt, with no concrete.
I'd have to go down an extra foot and fill that in with crushed stone - otherwise I'd have a REAL swamp down there. You normally hit water on this property just 4' down.
Then there's the hourly rate for a bobcat ......
On second thought, I think I'll leave well enough alone.