The EDACS system you linked to is indeed no longer active, however the frequencies attributed to it are still active.
The callsign
WPLU704 is still licensed to the SC Ports Authority, and that callsign is also associated with the
Palmetto TRBO system site #5 in Mt Pleasant. It's a DMR system.
When I was in the area back in December 2021, I verified that this site was active, but I didn't listen to it long enough to verify that this site carried radio traffic specifically related to the Port Authority. But that's where I would start.
Also, there are some active talkgroups on the Charleston County section of the
Palmetto 800 system (site 1-10, primarily) that carry some Port Ops. They're attributed to the SC Port Authority Police Dept. According to the database, they're in the clear (not encrypted) and I seem to recall that being the case when I was there in December.
I would also suspect that there are conventional frequencies in use (probably simplex, non-repeated) for port operations. If you're close, then you'll probably hear some of it. I'd focus on the
marine channels (for communicating with ships entering and exiting the port) as well as
UHF common business channels ("DOT" and "STAR").
Let us know what you figure out.