159.3975 is still active according to the FCC, however this is a old Police Freq when Plum did their own Dispatching and was a way for Plum to do police mutual aid with Murrysville. I have this old freq in my scanner and I don't see it in use. Plum Police, Fire & EMS are being Dispatched by Allegheny County 911 on East PD channel 2 .... 472.5875 pl 167.9 If you listen in Plum are cars 43xx and Penn Hills are 33xx. see above post for Fire/EMS info.
The original post was for a specific freq ch. 6. It is used very little as it is a GMRS . They have it listed as their ch 6 but I do not see a license for it. They may use it for Fire practice but Allegheny County 911 will not contact via this freq...
Brian