Remember Ego; NRCS soil survey samples are taken from a depth no greater than 60", often less. We took our samples (and I believe many do the same) with the excavator, reaching to a depth below the lowest point of the proposed pond depth. Based on what I see from your original topo, I think you are a dug pond so a dam won't be necessary...but...If a dam is required and there is questionable integrity in the soils within the pond basin, a core would likely be recommended and sampling the core zone to the same depth practice noted above would be wise.
Another huge help to me was the ability to secure the water well drilling records of close neighbors from the State website; usually buried within the State DNR section. In fact, I remember getting drilling records from areas where oil wells were tested. They were interspersed with the water well records. Anyway, if you can find these drilling records for activity nearby, they usually have a table of the soils encountered during the drill and at what depths.
