The Plum EOC/dispatch center is slated to close later this summer and I believe county 911 is taking over all dispatching duties for them as a cost saving measure. I think the old frequencies will be phased out totally at some point.
Plum fire departments have been with the county a couple of years. They are on East Fire 1 470.3875 PL 123.0, and respond on East Fire Ops 2 470.325 PL 131.8. They do have East fire and Mon Valley linked for now, and I suspect this is a temporary thing until they get the Mon Valley radios programmed, and get them phased in to the new system.