Dr. James McDonald referred to this case in his prepared statement before the House Committee on Science and Astronautics in 1968.  It was one of seven multiple witness events that he had mentioned. He listed it Case 13.

Apparently there were a number of sightings at this location. The Project Blue Book UNKNOWNS included a May 10 incident but it couldn't have been the one McDonald was referring to. The date was wrong and the number of witnesses was way off

"May 10, 1952; Ellenton, South Carolina. 10:45 p.m. Witnesses: 4 Dupont employees at the Savannah River nuclear plant. Up to four yellow, disc-shaped objects were seen on five occasions between 10:45 and shortly after 11:15."

"Georgia and Alabama led the field (in sightings in the fall of 1952). Many of the reports came from people in the vicinity of the then new super-hush-hush Atomic Energy Commission facility at Savannah River, Georgia. And many were coming from the port city of Mobile, Alabama. Our first thought, when the reports began to pour in, was that the news papers in these areas were possibly stirring things up with scare stories, but our newspaper clipping service covered the majority of the southern papers, and although we kept looking for publicity, none showed up. In fact, the papers only barely mentioned one or two of the sightings. As they came in, each of the sighting reports went through our identification process; they were checked against all balloon flights, aircraft flights, celestial bodies, and the MO file, but more than half of them came out as unknowns."