I don't envy you in the least. You have a nightmare job on your hands. If you get me anywhere near a hydraulic valve and I have a shovel in my hand I'm going to cut the supply tube in half. It's just too easy to do.
I've heard about a tool that can send a pulse down the pipe so you can trace it. I've never seen one so I googled. Maybe something like this will work for you on such a big job. Maybe you can rent one.
www.rjmcompany.com/Plastic-Pipe-Locator.htm