Hi Patrick,
Is the deepest part of the pond right up against the dam? I ask that because 16' is not trivial. That's a lot pressure, and extrordinary care must be taken to make the base of the dam thick enough and the dam tall enough to help pack it down.
How old is your dam?
When the dam was built, was the clay moist or dry?
When the dam was built, was the clay tamped layer on layer?
Was the dam keyed?
