Do you know relatively where the lines run and the splices are? If you have a high degree of confidence, you could leave the water pressurized for a few days, then try driving a steel pipe down near the splices to see if you can locate a soggy patch of sub-surface dirt - kind of like attempting to take core samples of soil. Obviously you want to make sure you don't inadvertently punch a hole in your electric or damage the line further - hence the need to know where the line is!