RS-485 over many 1000s ft, ground wire and termination always needed?
I would think it would be asking for trouble if you did not use termination and grounding. See Jan Axelson's write up. Also the further your cable extends, the lower the baud rate will be. At 4000' the maximum baud rate is 90kbps. I think using the shield as the ground is okay, but you need to isolate each node with 100 ohm resistors. I have used RS485 for short hops (~100' or so) without using termination or grounds, but I think for K's of feet you would be wise to stick to the rules.