I'd worry about the ground water that started appearing when you were excavating. If it is a spring or a seam from the creek, it will run both ways. Depending, of course on which is the lowest.
Also, when they hit rock, they may have hit a rock strata that goes to the rear of the dam and shows up at that point.
I see nothing to seal it but I would personally be very happy with only a 1/2 inch loss per day. Heck, I have that much evaporation.
