I'm not sure what agency that might be with a dispatcher in Williamston, but 18992 is part of the "SC EMS" series of talkgroups.
Previously, 19088 had been indentified as SC EMS Region 3, the Grand Strand area. 18960 is the SC EMS Statewide talkgroup. I suspect that 18992 is Upstate region, and 19024 is the Piedmont region. 19120 might be SC EMS in the Charleston area.
I assume that the SC EMS talkgroups are for EMS "mutual aid" state-wide. Probably for ambulance services and hospital ERs.
That's about all I know, and those talkgroups are only guesses.
Brian