Assessment of a radioactive waste disposal site at Enewetak Atoll

The 43 nuclear tests conducted at Enewetak Atoll by the United States between 1948 and 1958 produced close-in fallout that contaminated the islands and lagoon of the atoll with radioactive fission and activation products, and unfissioned nuclear fuel. In 1972, the U.S. government announced that it would conduct a cleanup and restoration operation to return the atoll to the Enewetak people. The radiological cleanup began in 1977 and lasted to 1980 and focused on reducing the concentration of the transuranium elements (238,239,240Pu and 241Am = TRU) in soils on some of the islands that might eventually be used for residence or for subsistence agricultural. The cleanup plan called for relocating soil and some other contaminated debris to Runit Island on the eastern perimeter of the Atoll. Some of the contaminated soil was mixed with cement and the mixture placed below the water level in the Cactus Crater that was formed by a nuclear explosion in 1958. The remainder of the contaminated material was mixed with concrete and placed above ground over the crater in the shape of a dome. A concrete cap was constructed over the dome of soil. Concern has been expressed by the people of Enewetak and by others over the possible aquatic impacts from the radionuclides entombed in the crater. A National Academy of Sciences committee examined the dome and concluded that the containment structure and its contents present no credible health hazard to the people of Enewetak, either now or in the future. The committee suggested that "at least part of the radioactivity contained in the structure is available for transport to the groundwater and subsequently to the lagoon and it is important to determine whether this pathway may be a significant one." Therefore, a surveillance program was started in 1980, in conjunction with other research efforts, to study the radionuclides in samples of fish, groundwater, and lagoon seawater. Our data and conclusions support the findings suggested by the National Academy committee over a decade ago in that any assumption of rapid remobilization of all or any of the dome's transuranics or other radionuclides is an extreme one. Any fear that this structure contains amounts of activity whose release would cause damage to the environment that will result in greater effect on human health is unfounded.