Because it’s in the FCC rules: “...Amateur stations will be permitted to commence operations after a 30 day period unless UTC notifies the station that its fix

Because it’s in the FCC rules: “...Amateur stations will be permitted to commence operations after a 30 day period unless UTC notifies the station that its fixed location is within one kilometer of Power Line Carrier (PLC) systems operating on the same or overlapping frequencies. This notification process will ensure that amateur stations seeking to operate in the above noted bands are located beyond a minimum separation distance from PLC transmission lines, which will help ensure the compatibility and coexistence of amateur and PLC operations, and promote shared use of the bands.”