Definitely been a wet one this year! We are finally drying out on the other end of the lake (I am about an hour north of you). From what I know about the soils in your area, you should have no trouble with finding clay until you hit that shale layer which is present everywhere but in the valleys. So preferably, if you do hit shale, make sure and set aside a fair bit of the clay to line the hole with after you achieve the depth you want. I would hate to see you go through all this trouble to expose a crack in the rock to which all your water flows.

From the ponds I have seen down there, they didn't even need bother with a key in the damn the soils are so jam-packed with clay. Wish my soils we like that!

We kept our pond <1 acre to avoid the DEC factor and needing to hire someone to design it. Good luck with your project!