Clarifying separation of ethernet cables from cables running power (underground)
You're not allowed to mix low-voltage and mains wiring in any way, shape or form in the same cables, conduits or raceways. The reason is safety: the data cables may not threaten the power cables, but melting or damage of the power cables absolutely could cross mains "hot" voltages onto your data cables.  

This is only allowed if the data cables and everything the data cables connect to is also inside Class 1 wiring methods.  Such as 24V latching-relay-based lighting controls.  Or 0-10V dimming controls run in the same conduit as mains.   Or ethernet used as SCADA between mains control equipment all mounted in Class 1 enclosures. 

What's not allowed is running an ethernet through a mains conduit, having the ethernet land at an Ethernet cover plate, and then proceed via Ethernet cable which is decidedly not a class 1 wiring method to a local PC, where it enters a data port not hardened for mains power.  

Anyway, as far as mains is concerned, "separate conduit and you're good".  If your conduit is metal, you probably really are good.  If it's plastic, then you might have signal interference if the signal is susceptible to 60Hz or whatever line noise is on the mains line; however the Electrical Code really doesn't care about that.  These days most electronic signaling is so high frequency that it seems unlikely that old mains line noise could have much effect.