grovers, please pardon my, uh, friends, uhm, and yes i am always dead serious especially about a leaky pond, they arent fun.
boy it really sounds like underflow. i'm not sure if compaction is as critical with bentonite, but sounds like he should have used a sheepsfoot roller or something other than just his equip, to compact. also, if he didnt get the trench deep enough, the bentonite wont help, but like he said it might take some time to swell and plug leak.
monitor the rate of the leak. obviously, if it decreases..great....if it increases and persists more than a few months, you still have a problem.
i fixed my underflow problem by putting a large clay patch extending from the lower part of dam (on the pond side) across the deepest parts of the pond basin. obvisouly this was done with no water in pond. IIRC, others here have had some luck patching the back (dry) side of dam.
good luck and post updates.
