Welcome to the forum!
I'm 5-6 miles to your NE as the crows fly. The bad news is that I'm a newbie with ponds too.
I'd recommend giving the DEC fisheries people in Avon a call. I emailed them about cattail control and while they gave me marginal news, they tried to be very helpful. At the very least they should be able to lead you to a soils expert. Speaking of the DEC, I think you're looking at an excavated pond. I don't know for sure but my guess is that they won't let you dam that creek even if you had the clay. There was a guy near us that built a pole barn in his back yard (literally 30 yards from his house). He had to tear it down because the DEC considered it "wetlands."
Regarding the water in your test holes... keep in mind that the whole area is pretty saturated right now. I have standing water in my yard. A word of caution: ground water ponds go low quick when you have a dry spell. This is really important if you can't get more than 9' deep. You'll want every inch of that depth as often as you can - especially going into winter. Mine went several feet low in June, July and into August. I'd much rather have a pond with a good seal.
I have a good deal of clay in my soils so you should be able to find some good lining materials fairly close. The geology is slightly different North and South of Ridge Rd. If I had the funds for a reno, I'd triple the size of my current one and tell 'em to dump the spoils in your yard!
It looks like there are several ponds near you (use Google or Bing Maps on Satellite view). Any luck talking to the owners about builders or soil structure? With a bit of luck you might become fast friends with a farmer that has some equipment.
You could also try to talk to the water department in your town or the one to your north. If they can't give you details on the soils, they'll at least know who does a lot of work in the area.
Sorry I couldn't give you more specific advise. I wish you the best of luck. Keep us posted, I'm very interested in how things turn out for you.
