Just had a pond dug/built. I would say the answer depends on how much clay has to be trucked in and how the dam was originally constructed. I would drive a freight train over my dam after watching how they built it. Are you saying the length of the road across the dam is 50 yards? If they can add clay and shape easily on top of it as is, I'd say you are looking at a day or two of dozer work plus the cost of dirt trucked in. If there are other structural issues where a large portion of the dam has to be reworked, obviously going to be a different story.