TG 7.5 monitors also manned checkpoints on Site Elmer when H&N workers were leaving or returning at irregular work hours. 4.3 Underwater Monitoring The use of underwater monitors during this Operation was an innovation in Rad-Safe monitoring procedures. The underwater monitors performed radiation surveys prior to work required of H&N divers. Three H&N Rad-Safe personnel were checked for physical fitness and swimming ability, and then were given instruction in the use of the Scott AquaLung. Also, the AEC Rad-Safe Assistant, having previous skin diving and swimming experience, became a member of this team. During the Operation the underwater monitors made 52 dives to depths varying from 15 to 85 feet. Radiation intensities in some areas of the lagoon bottom were found to be in excess of 50 roentgens per hour. The Rad-~Safe divers were instrumental in detecting and recovering a radioactive source that had been dropped from one of the shot barges into 85 feet of water, The underwater survey instrument utilized, (UW-1), designed by Riggs Nucleonics Corporation of Burbank, California, 50 r/hr. has a range of 0.05 r/hr to Figure 4,2 shows this instrument and other diving equipment used by the underwater monitoring team, 18