I've been pondering something for a bit, and thought I'd throw it out there and see if somebody has some insight. Water saturated soil can have some strange properties. If you've ever been to a beach and walked in loose sand at the waters edge and sank to your ankles, or been stuck in "quicksand", you get the idea. Could the found ransom have migrated from one level of soil to another because of buoyancy or density differences?
Normally, in mostly dry soil, I would say "no". But, because the area where the money was found was prone to be water saturated sand, could the sand become "loose" enough to allow lighter objects to float and heaver objects to sink?
Interesting notion, Nimi, and worthy of investigation. Then add that the bundolas were compressed and many bills stuck together. Did they all migrate upwards from a deeper, denser depth?
I used to run a company that picked rocks and cleaned beaches. It was named
Sandsifter, and the machines we used were modified potato harvesters. In that work I observed that the ground is not static, especially over time. Many things, such as rocks or bundolas, will float in soil and move upwards. I attributed this to long-term dynamics such as frost heaves, drenching rains saturating soils for short periods of time and creating a fluid mass - or a flood in the case of T-Bar.
Perhaps the bundolas were deposited by the dredge in '74 or so, then compressed over the next few years and by '79 and '80 had floated to the surface a few millimeters at a time?