Welcome back to the forum.

I think the next step is get a backhoe out and dig test holes. Soil survey maps are great for a broad overview, but for pinpointing there's nothing better than actually seeing what's there.

Soil on top could be poor for sealing a pond, but down 5' it might be great. Test and verify.

Even if the soil is poor, if there is a supply of clay somewhere else on the property, that could be used to line the pond and seal it.

www.hoosierpondpros.com

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).