Upon reflection of my previous post and not knowing the particulars of your situation, I should qualify:

If the bentonite layer is <6" thick or so, an offset disk may mix in too much sand and dilute the bentonite's "mojo". A light disking with a straight disk would be preferable. If the bentonite layer is very thin, 1"-3" you might be better off leaving well enough alone and hoping it redistributes itself into the prism cracks after rehydrating. It sure is tough giving good advice over the web and not looking at the project in person!

If the pond is dry you could take advantage of the situation and track in additional bentonite into the sidewalls up to the target waterline. The stuff is like snot when wet so it's pretty easy to tell if it's in a dry enough condition to work.