Update: We dug test holes today with a backhoe and there is two to three feet of gravely overburden under the 12 inches or so of clean top soil. Below that, there is rocky clay with average six inch rocks. My pond builder agreed we would have to haul away most of the overburden, or have a big eyesore. The pond would more likely than not leak. It is a no-go, we have decided. The other place we could build a pond that would definitely work and has good clay is right below and directly east of the existing pond, but is too far from the house (600 ft) to have good aesthetics. We wanted to see the water from our back porch and be close enough to run aeration, etc.
