PREPACE Between 1948 and 1958 Enewetak Atoll in the Marshall Islands was used for U.S. nuclear weapons testing and 43 devices were exploded there. In 1972 the federal government announced that it would rehabilitate the atoll and return it to the government of the Trust Territory of the Pacific Islands and, subsequently, to the Enewetak people, who had been moved to Ujelang in 1947, 125 miles southwest of Enewetak. The Pnewetak rehabilitation effort involved many departments of the federal government with the Defense Nuclear Agency (DNA) being charged with the major radiological cleanup responsibility. In the process of this cleanup, radiologically contaminated soil and debris from many of the islands in the atoll were collected and transported to Runit Island on the eastern side of the atoll. The contaminated material then was contained in a.soil~cement matrix in Cactus Crater, which had been formed by one of the nuclear detonations. This material was surrounded by a concrete key-wall and covered by a concrete cap. In order to provide the people of Enewetak and the Marshallese government with an objective assessment of the safety of this contain~- ment structure, the DNA requested the National Academy of Sciences, through the Advisory Board on the Built Environment” (ABBE) of the National Research Council, to “assess the effectiveness of the Cactus Crater structure in preventing harmful amounts of radioactivity from becoming available for internal or external human exposure"; the DNA added later that this assessment should be "set against an under- standing of the expected living patterns of the people of Enewetak in terms of their degree of contact with Runit Island and their exposure otherwise to residual radioactivity on the atoll.* The committee appointed to conduct the study concentrated primarily on two issues: (1) the potential hazard of transuranics being trans- ported to the surrounding environment from the structure in its present configuration, and (2) possible sequences of events that could affect the structure's physical integrity and an estimation of radioactive hazards that might result from the dome's breachment. ‘Two subsidiary issues also concerned the committee and are commented on in the report; _ Mamely, possible hazards associated with the quarantined island of _*Pormerly the Building Research Advisory Board (BRAB). reel J004311