I have thought about this also. There are actually several gravel pits in the area along a live creek my property borders. I'm sure that I could sell it off in markets around me. Will the clay adhere properly to the side walls of some sand and gravel? I am also in the process of having someone determine if the rainfall in the area would be equal to or greater than the amount lost to the sides. Or maybe digging a well or possibly pumping in the water from the creek to keep up with the loss. I am scared to think of the cost of lining a 20ac site with a 20ft depth of water with clay. I have even thought of downsizing some of the depth to make it more viable. Maybe I need a lottery ticket.....