I have installed liners in leaking ponds in the past and sealed up a few bad spots with bentonite but never did an entire pond with bentonite before, I know how much to put down but was wondering if spreading soil over it after tilling and compacting is recommended, I have seen it both ways but any advice or past experiences would be greatly appreciated.
Nick, Bentonite tends to become colloidal and not settle out of the water....I'd add a foot of good compacted soil over the properly tilled/compacted bentonite mix if I were doing the job.
I have a lot of experience with bentonite but in a different area than ponds. I look at it like this. Bentonite is a clay and one wants a layer of clay on the bottom of the pond so it will hold water. I would add a layer of clay, not disk because that would dilute the clay, pac the clay down and then I might add some soil on top of the clay to reduce the bentonite mixing in the water and becoming a colloidal or water suspension problem. I am no pond seepage expert but that is how I would do it.
Due to my past experience, I have no advice. But, you can call Texas sodium bentonite for advice. The owners name is George. Don't remember his last name. Nice guy.
I don't think you would hurt anything by adding additional clay on top of the bentonite. I just finished up patching a rocky area in my pond that I believed was leaking. What I did was remove dirt over the rock, applied bentonite in power form and covered it back up with dirt. I then used my disc to work some in on top of the dirt too and pack best I could with my tractor. Then I pulled in clay from above the leak for added protection.