Thank you everyone for all the information! I know I've still got a long road ahead, but getting these questions answered makes me feel much better.
I did talk to my closest neighbor, his pond is 3-4 acres and is 550 yards west of our proposed site. He said his pond was built by selling the sand (as FishinRod mentioned above). He's had more sand removed every few years. I haven't asked him yet if he found clay at some point. But he doesn't seem to be super into the pond as far as being concerned with the details.
I should add that we had soil borings done near our pond. Closest one was about 25 yards north of the proposed pond edge. The soil borings were part of an environmental study we had to have done when purchasing the property. Our property has an old township dump on it (also no soil can be removed from the property, i.e. sand). I asked the environmental consultant what type of soil was in the sample near the pond area. They said there was "a silty type of clay" about 10 ft down. These borings were done at the grade, not in the basin, which would put the clay in the basin only about 5-6 ft below the current sand level in the basin (I'm hoping).
I left a voicemail with the local NRCS office today regarding watershed information. Hoping we can get a mini ex to dig some samples yet before winter. This last spring/early summer (which was a dry one) it was June before we were be able to get any type of equipment out into the pond area due to it staying wet.
I attached a couple pics just for the heck of it. The October picture (taken standing on North side of pond) from last weekend is current state of basin. Only two 1-2' deep water pockets are present, one right up front and one way in the back. The March picture (taken from West side of pond) shows how much water it has in the spring. The island that was left is about where the pile of sand is we have since created shown in October pic.
I'll post an update when I hear back from NRCS. Thanks!
