One site is a water reservoir, the other is a pump station and pressure relief valve down the hill from it. I don't believe there's line-of-site available. The pump station either has or will be getting a DSL internet connection; it looks like the 2km cable is newer direct burial and my understanding is that it was just pulled in, probably replacing an old telco line.
There will also be a wireless link (UBNT AirGrid) between the reservoir and another several KM away; each reservoir has a small NVR and two cameras, as well as an alarm and a Viscount "nanocube" access control module that are currently running stand-alone.
Currently the output relay on the nanocubes, and an intrusion switch into the wells, tie into the SCADA system that relays data back to the city works yard, one input for the switch indicating the hatch has been opened, another to signal that a valid fob has been swiped (it doesn't actually GRANT access, it's essentially just replacing a keyswitch that used to "disarm" the alert). There's generally up to a 10-minute polling delay with SCADA though, so the hope is that all three will have internet access from the city works yard... not necessarily to live-stream the cameras or record off-site, but just to have access to them if necessary. Of course, it would also facilitate adding/deleting fob users from the connected sites without needing to visit them.
We've looked at a wireless link direct back to the works yard, and there SHOULD be line-of-sight from one reservoir or the other... MAYBE. The SCADA system relays through several different sites to get back there, though, and matching that path with the UBNT wouldn't be practical. We figure since the pump station will have internet, and already has a wire in place to one reservoir, it would be silly not to investigate linking the two with that.