Thanks for the reply Scott.
I built my pond with a fel, it was slow but kinda fun. I dug and then built the dam side up in lifts of 6-8 inches, compacting as I drove over it. Mostly all a shale/clay mix. I removed all the top soil before starting. I dug down until I encountered a solid layer of shale. I put about a foot of shale/clay back over the solid rock layer and compacted it in. Makes my pond about 7 foot deep if it ever reaches full fill to the overflow.