Brettski,
Thanks for your reply. I did not see that. The pond was excavated from a small stream valley with a lot of fall from back to front as we are in hilly country.
The dam was going to be really high so I doubt(?) he dug down alot deeper at the base of the dam. This is what I think you mean by coring-a 4 to 8 foot trench basically parrallel to the dam at the base- not perpindicular to the dam along the streambed?
These replies have been great. I wish some of you guys lived closer to me!