I have a question for Otto or anyone else who can answer. I am currently cleaning out what will be a 3 acre pond. By looking at soil types while diggingit looks like a small creek was dammed without much excavating except for the dam. I am digging down to sandstone and stopping. Some places soil/muck is 3 feet but up to 8-10 feet deep. I have breached the dam. My question is how close do I get to the dam excavating down to sandstone and do I do anything at that junction to prevent leakage?