I am digging a trench across my dirt, or sand, driveway to run a 2" pvc water line. How deep do I have to dig? I am planning on running the line in some bigger 4" old pvc in the actual driveway area. Do I really need to do that? There isn't that much traffic in my driveway. I am doing that all by hand so I want to make sure I don't dig too deep. LOL Appreciate any suggestions. This is my first time to run any kind of pvc line.