hey joe, i know a little (that was a great skynard song), but its hard to give you exact answers for the reasons rocky states. that said, water tables usually fluctuate on a seasonal basis. in my neck of the woods, they can vary over 10 vertical feet from spring to winter. if you built the pond to hold water at levels higher than the water table, and did not seal off the water table, the pond would seep and lose its water until it re-equilibrated with the level of the water table. the rate of loss would be completely dependent upon the shallow subsurface geology, but it sounds pretty high based on the rapid re-charge into the test pits.
as rocky said, sounds like the choices are
A) to dig out the pond so that the high water mark corresponds to the current water table level(hoping yer water table doesnt vary much seasonally), or
(B) construct a high sided dam and line the bottom with compacted clay soils above yer current water table level.
