74 Planning and Programming RADIOLOGICAL CLEANUP OF ENEWETAK ATOLL Task Group were Mr. Tommy F. McCraw (AEC Operational Safety), Drs. W. Nervik and D. Wilson (LLL), and Mr. W. Schroebel (AEC/ Division of Biomedical and Environmental Research). The Group was assisted by average exposure rate was defined for each island. When an average rate was neededfor a group ofislands, it was obtained by weighting individual island rates according to the area of eachisland in the group. The exposure rates were converted to absorbed dose based on assumed duration of seven consultants. All members and consultants workedeither directly for the AEC or for an AEC laboratory, and most had been associated with AEC efforts at Bikini Atoll. Liaison representatives of DNA, EPA, and DOI attended the Task Group meetings. The AEC Task Group’s findings were compiled in a ‘‘Report by the AEC Task Group on Recommendations for Cleanup and Rehabilitation of Enewetak Atoll,’ which was circulated in draft form for comment in February 1974 and, after revisions, again in April 1974. There was lively debate, even among the AECstaff, over aspects of the report. Typical points at issue were: the appropriate contamination threshold for removal exposure. Inhalation dose estimates were determined using the InternationalCommission on Radiological Protection (ICRP) lung model. Intakes to this model were derived from concentrations of plutonium in soil and an assumed air-mass loading. (Average concentrations for plutonium in soil of islands/group of islands were used.) This method was considered preferable to using thesurvey air sample data, which were representative only of a very short period of time. Had actual air sample data been used, inhalation dose estimates would have been several orders of magnitude lower than reported. Ingestion dose estimates were based on an assumeddiet (including local marine andterrestrial food and imported food) and measured or derived of soil from Runit and Boken, the scientific or technical basis for making a judgment that plutonium levels in the soil on Runit and Boken were high enough to justify removal of large amounts of soil; and the limited (3 weeks versus an annual program) air sampling data which indicated that airborne plutonium levels at Runit were quite low, comparable to some concentrations of radionuclides in components of the diet. Significant radionuclides for ingestion dose were determined to be cesium-I37 and strontium-90. A concentration for these nuclides was determined for the average fish ofthe atoll, for use in estimating doses via the marine food pathway. The concentration of the significant radionuclides in terrestrial levels in the United States.56 Dr. William Ogle, an eminent scientist long associated with the nuclear test program, was consulted by DNA on the Task Group Report. He questioned the recommendation that the dri-Enewetak be kept off Enjebi foods was estimated primarily by correlation between concentrations of radionuclides in soil and in indicator plants or animals. The survey report included estimates of annual dose rate ‘and until subsequent AEC measurements and analysis indicated that they could return to that island. His concern was based on the belief that the U.S. would not be in control indefinitely. He recommended that cleanup actions be taken which would allow the dri-Enewetak free use of the atol! in the future. Regarding Runit, he felt there was every reason to suspect that the problem was caused by small particles of plutonium. He accumulated dose. over extended periods of time for the various living patterns. The effect on possible dose due to cleanup modifications, e.g., covering contaminated soil with clean soil, plowing soil to mix contaminated surface layers with cleaner subsurface layers, was assessed. The report ranked dose pathways in the following order of decreasing dose: ingestion of terrestrial food, external gamma exposure, ingestion of questioned the need for the dri-Enewetak to stay off Runit.5’ He realized that the AEC recommendations assumed there was a genuine hazard, but he felt that the information available did not fully support that assumption. He felt that Runit should be cleaned as well as possible and turned over to marine food: and inhalation of contaminated air. The most significant contribution to dose via the terrestrial food chain was determined to be strontium-90 in pandanus, breadfruit, and coconut.*° The Enewetak Radiological Survey provided a data base and general concepts for radiological cleanup. Considerable effort was still required, however, to evaluate and adapt the data for actual cleanup operations. the people.>8 . DNA believed that the recommended cleanup standards (in terms of residual radiation) were too low (that is, too conservative), that cleanup to these levels was not necessary, and that the funds likely to be made available for cleanup would not permit reducing residual radiation to these In July 1973, an AEC Task Group was appointed by the Director, Division of Operational Safety of the AEC, to review NVO-140 and to prepare cleanup and rehabilitation recommendations. Members of the we ee AEC TASK GROUP REPORT: JULY 1973-JUNE 1974 75 levels. In commenting on the April 1974 draft, one AEC office expressed the belief that the plutonium cleanup could be generally characterized as ‘‘reduction of plutonium contamination accessibility’? and recommended that no numerical guides be published for residual plutonium levels in soil except those essential for guidance of a group of experts in the field to