nathan, the thing about springs in the bottom of a pond is that yes, they could maintain some amount of water in the bottom depending on the flow rate of the spring, but keep in mind that once the pond water reaches a certain depth (or height above the spring) the pressure of the pond water (against the spring entrance) can exceed the pressure of the spring (coming up in the pond) and cause reverse flow back through the spring and into the ground. this in turn (in the absence of rain) makes the pond water level drop (usually pretty fast) to the level at which the pond water pressure equals the spring pressure.....which is typcially really low.
a lot of people here when they find a spring (or water table water) in the bottom of a pond, they pack it off and seal it with clay and hope it doesnt leak.
since it sounds like you have good clay soils around the pond basin, it appears it wouldnt take too much to bulldoze that stuff around, pack off the spring, and essentially "renovate" at least the deepest area of the pond. maybe there could be an allowance in the purchase price for this?
