I believe 64816 is one of the new Type II talkgroups for the County Public Works department. I am showing a lot of activity on it (approx 5000 comms). It might possibly be the engineering department. Looking back through the log file, it looks like a lot of the radio IDs that use this talkgroup also use FF3 (65328) and FFB (65456) both of which seem to be more active than FD3 (64816).
John