I have a feeling after reading that document that HMARS does not have it's own dedicated TRS, but rather has reserved talkgroups across the area's various local radio systems (kind of making an educated guess here). When they mention 700Mhz system, I'd bet a dollar they're referring to the DC TRS. If you look at the various systems around the area, there looks to be a few that list HMARS talkgroup(s). The radios mentioned probably have a zone programmed for HMARS and possibly nothing else, and just affiliate with whatever system is closest depending on their location. Those talkgroups are just simulcasted among the various radio systems that carry them and also via a private telephone system. Just like med channels are used across a particular region, but are accessible via any local trunked radio system.