I appreciate all the advanced science of soils, believe me, but see nobody saying, some clay breaks down a bit, when submerged, and blend with other soils, making them more clayish, hence making these blended soils, in combination, tend to seal.
I've heard of ponds filling two or three times and leaking all the way down before a seal is made. I do think Bill has the right answer though, don't trust your pond to time driven sealing. Compact it down with good clay and seal it yourself.
Interesting thread.
