Wes,

I use USDA publication 590 as my "Bible" for pond construction. On page 63 of that reference is the following statement for thickness of a clay liner:

"Thickness of the blanket depends on the depth of
water to be impounded. The minimum compacted
thickness is 12 inches for all depths of water under 10 feet."

Personally, I have talked to many pond guys in my area and the consensus among them is 2 feet of compacted thickness. If it were me, I would error on the safe side and go with 2 feet even though that is a lot of clay. Good luck and please let us know what you decide and how it works. Thanks.

p.s. you can download that pub from their website...or I would be happy to forward one to you.