Just call 811 and let the utility figure it out.
Reps from the local telco showed up to one of the meetings to tell everyone that they didn't know where their copper lines were buried and that they were unsuccessful at locating them outside at all. They knew where both ends were but the middle was a mystery to them.
This statement made the architect's face contort into strange shapes. I joked that they call 811; some people thought that was rather hilarious, others much less so.
Anyway, the building wasn't in service yet and the telco said they'd fix it if we managed to naff them up, so away we dug. No telco cabling was damaged in this process. (We did dig up some plastic drainage tile but that was a simple farm store fix.)