My pond is now drained and the leak looks like it has stopped because there is barley any pressure there now.

I think I will try like Cecil did and dig with the trench bucket on the backhoe and use that as a form? If I do find a little water going past the pipe, would it affect the concrete when I dumped it in?

I am also thinking of lining the top, bottom, and sides with bentonite.
Bentonite gets really soft when wet though. Good idea or bad idea?

Thanks for the help!