Got scared enough I decided to do a Geo Survey. First picture is next to spring fed creek in centerline of dam. Do not have results back yet but 1-3' was sand, 3-5' was a water reservoir, at 5' started into a mix of clay/sand and at 8-13' looked to be very good clay, at 15-20' turned into pure white dry sand. My initial interpretation is that the 5' thick clay layer is holding water above it and as long as we do not break through that layer on the core trench I should have a nice seal. My borrow area material looked to be a dry clay/sand mix and I hope it will work as no other material is close enough to make the project feasible. I will post results of soil analysis when I receive them.
