A guy I talked to a number of years ago about digging a pond in sand/gravel (he needed the material for a private road) said he works silt in to the sand/gravel and compacts it. Said it helps with a sand/gravel pond to seal itself.
I was reading some stuff this morning, and apparently, it is a practice.
I didn't buy it at the time, but may be something to investigate further. Maybe only to slow down the leaking. Only sources of water available are water table and pumping from a well. Virtually no runoff. EPDM liner is about 35-40K
