I do seem to be gradually tracking down the problems and getting them fixed, and each time I do I seem to end up with another permanent gain of a few inches of water.
I used the bentonite in 2 ways. In the winter when everything is wet I used sticks or even the baseball bat to make 2 or 3 foot deep holes where the dam was mushy and I poured and rammed bentonite into those holes in the hopes of firming things up. Even though we built the dam in September, it was still too wet to properly compact, so that is the problem I have been having to deal with. As the dam dried out and developed small cracks I discovered some of them went deep enough I could pour in several gallons of bentonite soup, and if I let it dry out for a week I could do it all again. At the end of the summer those same cracks would only have room for a couple cups of the mixture, and I reasoned that the air spaces I was slowly filling up with bentonite residue as the water dried, were the spaces that were transmitting water when the pond was full in the winter.
Bentonite seems to need to be confined by something to hold it in place. If you put a cup of dry granules in a bucket of water it just turns to soft liquid mush. When you pack it into a confined space, its swells and it's own swelling prevents it from absorbing enough liquid to loose the solidity it needs to withstand water. I wonder if putting bentonite into a bunch of gelatin capsules which slowly break down, would be a way to get the bentonite to go deep inside a leak, before it began to swell?
The tamping I did was to compact natural clay, not the bentonite. From what I have seen, I don't think bentonite is really the best material for compacting. I'm not even sure it would compact at all.
My dam is on the south of the down hill side of a slope, and this last leak was on the east side in the natural soil, just above the solid clay subsoil. I was worried that side would always leak, once the water got above the solid clay, but the topsoil has a high clay content and it doesn't seem to loose much through there. It seems the water just found one place that let it through, and gradually created a good sized hole for itself. Because it's in natural topsoil and there is some rocks, it's not so easy to compact it. Because there was an obvious hole with a current, trying to block it up with acrylic wool seemed the best bet.
For compacting I have come to prefer a heavy axe head. But a light weight wooden baseball bat is nice to smooth this out.
It sure does look nice when it's totally full.
