Originally posted by patrick:
the bowl of the pond was excavated approx. ten feet below grade.
That makes a huge difference. 6' is minor compared to 16'.
If there's no sand or gravel beneath the dam piping water beneath it, chances are it needs compacting.
Soil is very heavy, and self compacts pretty well under its own weight. When soil is under water, the self-compaction is negated somewhat because it's much lighter when it's under water.
One way to apply pressure to the soil is to build the dam up 2-3 feet higher than needed. That will apply huge forces to the dam's base, and will help compact it. Of course you will need a large stand pipe or emergency spillway.
If water is seeping out well down the hill from the dam, you have a bigger challenge ahead.
