Where the dam meets the bowl can be a problem area if they did not get proper compaction or marry the two different materials together well enough.
When the snow gets off and the ground dries up, walk the back side of the dam where the dam meets the original earth. Look for leaks there.
Where the water is getting to a certain level and not going any higher, pay particular attention to the area behind the dam that would be at the water level or a little below. Might even be just one spot causing the problem or they might not have brought the core trench far enough the perimeter so that particular area has no core to tie the subsoil in with the dam material.
Hopefully it heals itself or you find the leak and it is a relatively easy fix. Sometimes it is not.
