I might use a plastic trench liner keyed into the clay in the bottom. At any rate, I will wait for the pond to leak down so there is no water in the trench. When it leaks down to the excavated portion, the leak stops. I would try soilfloc again, but am unsure if it would be the proper remedy for the kind of leak I have, plus there is almost no suspended clay in the pond water, plus lots of FA on the bottom.

Edit: I drove 3" PVC standpipes about 4 inches into the hard clay in the bottoms of the test holes, and dipped he water out of the pipes. The bottoms of the pipes have not accumulated any water. The water is standing about 16" deep on the outsides of the pipes. I guess this proves that the water is seeping under the dam between the bottom of the clay that forms the dam and the impervious layer about 16 inches below. Also, if that lower layer was pervious, the water wouldn't still be standing on the flat behind the pond over two weeks later.

Probably the old part of the dam built about 60 years ago was never cored.

Last edited by John Fitzgerald; 03/17/18 02:56 PM.