TL;DR: Does burying a cable provide shielding? I.e., is a shielded cable in air equivalent to an unshielded cable buried ~ 6 inches in soil?
Long: I'm a technician at a university. I don't have formal training in electrical engineering, but one of my tasks is designing an environmental monitoring system for the field. Analog voltage sensors (thermocouples) will be read by a device in the field, and the signal will be passed ~100 m to a datalogger via shallow buried cables. In selecting these cables, I was concerned about voltage drop (since thermocouple signal is a very low voltage to begin with) and cable shielding (since there are power transmission lines in the area, and AC power supply for the datalogger in the same enclosure box). I asked a more experienced technician for advice, and he advised that in this application he would be concerned about both things.
However, when I approached the project manager about this, I was told not to worry about voltage drop (no reason given), and that burying an unshielded cable was "the same as shielding it". I can order unshielded cable and spend no further time on the issue... but I'm concerned that the manager is just trying to save a buck, and that this could come back to bite us (i.e., I'll be creating more work for myself) in the future.
I'm also generally curious. Is he correct in saying that a shielded cable and an unshielded cable buried less than 6 inches in soil are equivalent?
*Edit to add detail: the site is a pine forest with well-drained (dry), predominantly sandy soil. I don't have much experience to go on, but I would say it's fairly quiet for EM. There's one high-power line ~200 m from the thermocouples, and 120V AC running through outdoor extension cords - the 120V lines are co-located, and will run alongside the TC's in some cases.
**Edit to clarify: I'm not concerned about voltage drop on the thermocouple itself. I'm concerned about drop on the 100 m cable that will carry the signal from the thermocouple voltage-reader (a Campbell Scientific AM16/32B multiplexer) back to the datalogger (a Campbell CR1000).