Is it possible it's not so much a leak but the fact that the watershed is insufficient to keep it from evaporating? Or a combination of both? I honestly don't see how that pond would stay full being 2 feet above the rest of the watershed.
In my area if the sand vein is quite small it would be much less than $5,000.00 to pack in some clay over the vein. I only paid $300.00 to have my 1/2 acre pond dipped a few years ago!
