For 60Hz and modern, in the sense of Ethernet, they should be close completely immune. A voltage induced on D+ will also be induced on D-, and the difference will remain constant. If there is going to be a problem it will be on non-differential lines, like RS-232, and not differential lines, like Ethernet, RS-485, RS-422, etc.In metallic conduits, none. In non-metallic conduits, little.
Modern data lines are almost immune to 60 Hz interference.
Lol " lessor separation may be used when the parties concur" . We should have concurred!National Electric Safety Code [C2-2007] Rule 320 Location B. Separation from other underground installations