Bill,
In my case, our 5 acre footprint was a very gradual oval bowl with one narrow end that remained low, between 2 hills, where the dam was constructed. The majority of the basin was filled with hundreds of years of run-off sediment in the form of topsoil and silt. There was so much that we elected to leave alot of it within the pond. We had to cut thru 6 - 7 ft of this soil to get to the thick blue clay layer below, extracting this clay to line our built-up building site pad. I will say, tho, that this 6 - 7' layer was the thickest area of topsoil/silt. It was 3 ft thick at the other end, near the dam. As we moved up the slopes to the level where the water level would terminate as a shoreline, the layer was about 10" thick. When I quizzed my contractor on whether this would be an issue, he explained that the water would soak into this loose soil until it hits the clay liner waiting below.
