The Port of Charleston South Carolina is operated by the state of South Carolina. One of its serious limitations is there is no direct rail access. Both CSX and Norfolk Southern have rail yards in the area, but containers have to be taken back and forth one at a time.
http://scspa.com/facilities/facility-features/
Much of the ocean traffic in the area is for the BMW plant nearby, and the Coast guard.
The North Charleston port is little closer to the railroads, but is primarily a bulk cargo port. It’s also further inland, and subject to tidal currents and bridge height limitations