Report by the AEC Task Group on Recommendations for Cleanup and Rehabilitation of Enewetak Atoll, June 19, 1974

Page 2

The Task Group wishes to thank all those who participated in development of input material for this report and particularly the Interior, and Defense Nuclear Agency for their comments

Page 3

Table of Contents Task Group Statement Concerning The Radiological Radiation Criteria Recommended By The Task Group . Assessment of Doses and The Results of Alternative Disposal of Contaminated Material .......... Task Group Observations and Conclusions .i..... Enewetak Radiological Sumey Report, Summary of Review of Radiation Protection Standards ...... Attachment I, Relationship Between Resuspended Plutonium in Air and Plutonium in Soils ......

Page 4

REPORT BY THE TASK GROUP 011?JZCO>!MEHDATIONSFOR On September 7, 1972, the Atomic Energy Commission (AEC) agreed to provide radiological criteria for cleanup and rehabilitation of Enewetak Atoll to the Department of Defense (IXID) and to the Department of Interior (DOI) . AEC also agreed to conduct a comprehensive radiological survey. The purpose of the survey was to gain a sufficient understanding of the total* radiological environment of Enewetak Atoll to support judgment as to whether all or any part of the atoll. can safely be reinhabited and, if so, to describe cleanup actions to be taken by DOD and any constraints. These tasks are identical to those performed for cleanup and rehabilitation of Bikini ‘Atoll and that experience has greatly aided the development of recommendations Radiological survey field operations were conducted between mid-October 1972 and mid-February 1973. Samples taken in the field have been analyzed and complete results of the survey have been published as a Nevada Operations Office document (NVO-140), Enewetak Radiological Survey, Vols. I, II, III. An abstract of NVO-140 is presented as Appendix I of this report, and the “Summary of Findings” chapter is reproduced here in Appendix II. In July 1973, a Task Group was established to review the survey findings and to prepare cleanup and rehabilitation recommendations for consideration Advisors and consultants to the Task Group have included Dr. E. Held (AEC/REG), liaison representatives from DNA, EPA, and DOI attended Task Group meetings.

Page 5

The job of the Task Group is to recommend for consideration by the Commission, radiological criteria for cleanup and rehabilitation of Enewetak Atoll and to recommend those remedial measures and actions needed to reduce exposures of the Enewetal: people to levels within these criteria. The objective is to keep exposures as low as practicable. advisors, and consultants have carefully reviewed the AEC results; current information on the life style, diet, and The Task Group, preferences of the Enewetak people; applicable radiation protection guidance established by various national and international radiation standards setting bodies; and current laws and regulations pertaining to The recommendations that were developed are those of the Task Group, advisors, and consultants, are most disposal of radioactive that, in the judgment appropriate for the U.S. Government to take to provide a radiologically acceptable environment for the Enewetak people considering they will be long-term residents on the Atoll. Recommended measures for Enewetak Atoll are very simular to those that guided cleanup and rehabilitation of Bikini Atoll. TASK GROUP STATEllENT CONCEIUTING THE RADIOLOGICAL SURVEY RESULTS After thorough review of the Radiological Survey Report, the Task Group makes the following observations: o The survey provides an exceptionally complete data base for estimating radiation doses. It includes the results of an aerial gamma radiation survey of land area plus radiochemical data from the analysis of over 4500 samples of air, soil, vegetation, sediment, water , and marine and land animals.

Page 6

l The survey report, plus the Master Plan for Rehabilitation and resettlement of Enewetak Atoll*, provide information on possible living patterns and diet of the Enewetak people. . l Seve~al important components of the Enewetakese diet are either not now available on the Atoll, or are available in quantities which are small compared to available at all, now; pandanus and the needs of the people. but will be reintroduced. tacca are growing only in Pigs and chickens are not No breadfruit is growing scattered locations; and coconut is growing in quantity only on the southern islands. Breadfruit, pandanus, tacca, and coconut must be planted and will begin to produce crops after about 8 years. Radiation dose estimates for these foods have had to be based on correlations with plants and animals now present on the Atoll and on inferences drawn from earlier surveys on Bikini and Rongelap. There are many data points, and these correlations provide the best method currently available for estimating internal exposures. Nevertheless, the method is not as reliable as direct measurement of the foods produced in the areas o Air sampling at Enewetak, accomplished largely during a 3 week period in December 1972 on uninhabited northern islands, showed extremely low levels if airborne rad~oactivity. Comprehensive air sampling during 12 consecutive months under conditions closely approximating data on which to and soil disturbance would provide more accurate base inhalation exposure estimates. *The report, “Enewetak Atoll Master Plan for Island Rehabilitation and Resettlement ,“ (3 Vols.), Holmes and Narver, Inc., Nov. 1973, contains information on the preferred living pattern for resettlement of Atoll obtained prior to completion of the AEC evaluation of radiological survey findings.. The people are to be given another opportunity to express their views on the remedial actions under consideration by the .4EC after they have been informed of radiolo~ical conditions in the Atoll, and the subjects of radiation exposure, radiation standards, radiation protection objectives , and remedial measures and their effectiveness have bpen diycussed.

Page 7

The Enewetak people advise that catchment rainwater is ‘the customary principal source of water for human consumption. Except in emergencies, water from underground lenses is not consumed. Samples of underground water were not obtained during the survey, and radiochemical analytical data on lens water is limited to that obtained from a few samples taken on JANET in 1971. A thorough lens water sampling, analysis, and assessment program requires sampling through a full rain-dry season cycle, 12 consecutive months at a minimum. Arrangements for sampling fresh water lenses are being made. This work will be done It is the opinion of the Task Group air sampling or lens water sampling results of additional would not significantly change the dose estimates in NVO-140 nor change the recommendations of this Task Group. RADIATION CRITERIA RECOMMENDED BY THE TASK GROUP A review of the radiation protection standards and guides considered by the Task Group to be applicable to Enewetak is presented in Appendix III. This review indicates that the numerical standards and radiation protection philosophy of both national and international standards bodies are similar. Summarizing that appendix, the specific guidance and criteria used by the Task Group in its assessment of the data and recommended for cleanup and rehabilitation of the Atoll, are as follows: The population dose to the Enewetak people should be kept to the minimum practicable level. The Federal Radiation Council (ERC) Radiation Protection Guides (RPG) for individual and gonadal exposures are recommended as the criteria to be used in evaluating the various radiation exposure

Page 8

numerical guidance therein should be reduced by the percent for individual exposure and 20 percent for gonadal exposure considering that exposures cannot be precisely predicted. The detailed rationale for these reductions is provided in Appendix III. The resulting guides for planning cleanup actions will then be: lhole body and bone marrow - 0.25 Rem/yr Gonads - 4 Rem in 30 yr o Since there is no adequate scientific information which would support general guidance for cleanup of plutonium contaminated soil, guidance can only be developed on a case-by-case basis using conservative assumptions and safety factors. With this in mind, the Task Group recommends the following for use in making decisions concerning Pu cleanup operations at Enewetak: b. 40 to 400 pCi/gm of soil - corrective action determined on a basis* considering all radiological conditions. of soil - corrective action required. ASSESSIIE1{TOF DOSES AND THE RESULTS OF ALTEPJIATIVE CORRECTIVE ACTIONS The Task Group approach for development of judgments and r.eco~endations for the radiological cleanup and rehabitati~n of Enewetak was to consider a number of alternatives for exposure reduction that may be feasible. Basically, the procedure involved four steps: *See Appendix 111 for additional guldace.

Page 9

Assessment of doses for a population living on the Atoll in its current radiological condition. Assessment of dose reductions that tight be expected due to modification of the diet. Assessment of dose reductions that might be expected due to removal of contaminated soil. Comparison of these dose assessment. matrices with the population dose guidelines used by the Task Group. The Enewetak Radiological Survey Report (NVO-140) contains estimates for average population doses on the Atoll for 5, 10, 30, and 70 years in its current radiological condition and for six living patterns covering a range of exposure conditions and including the pattern considered to be most representative of the Enewetak people~s desired life style after they return. are made for each of these living patterns for each of the followin,q corrective the village area and plow the village island. pandanus and breadfruit from the southern islands (ALVINfor inhabitants of the northern islands. pandanus, breadfruit, coconut a~d tacca from the southern o Import pandanus, breadfruit, coconut, tacca, and domestic meat from the southern islands. The estimates for 30 year whole body doses in the Survey Report are summarized in Table 1 of the Task Group report, and 30-year-bone dose estimates are summarized in Table 2. Note t’hat the option for “Gravel Village Area - Plow Village Island,” achieves a minimal reduction in radiation

Page 10

whole body and bone for all living patterns, and those Ilvlng on have to import most foods to avo}d exceeding a whole body 4 reins in 30 years. Population dose guidelines used by the Task Group include annual dose rates as well as 30 year integrals for genetic doses. Appendix IV provides a detailed description of thecalculations leading to estimates of maximum annual exposure for the critical organ of the segment of the population expected to receive the highest exposure. A detailed assessment of dose was made considering dietary changes that can be expected to occur with time and with age as these would influence dose to the fetus, the newborn, to children, and to adults. Estimates are developed both for persons who are adults when they return and for children born after return of their parents to the Atoll. Dynamic situations were evaluated such that exposures in the highest year are predicted. These estimates are not therefore average years should be lower than the predicted dose. Conservative values have been selected for variables in models for assessment of expected doses. Though conservative, the estimates are not considered ultra conservative and do not constitute the theoretical maximum credible or worst case exposure. These conservative estimates of expected maximum annual exposure presented in Appendix IV are considered by the “la.skGroup to be applicable to individuals in the Ene.wetak p~pulaticr.. There will be few persons within this population at any one time who are fetus, newborn, or infants, believed to be the most sensitive members. Therefore, the predicted exposures are judged suitable for comparison with FRC exposure guides for individuals within an e~”osed population. Tables 3 and 4 show estimates of the maximum annual whole body and bone dose.

Page 11

In considering the reduction in exposure that may be ac ~evable throughL“ removal of contaminated soil, the Task Group has taken the position that these predicted exposures are approximations only. The effectiveness of such actions to reduce ‘internal exposures that come through the food chain must be confirmed through analysis of test plantings. The Task Group does not favor soil removal as a dependable or feasible exposure reduction action for the dietary pathway. However, such action is reviewed in the Task Group Report in order to present a complete picture of the various possibilities considered. In its assessment of dose reductions that might be possible due to removal of contaminated soil, the Task Group posed the following question: “Given the dose estimates of Tables 1-4, and the dose reductions that can be expected due to the indicated actions, can equivalent dose reductions be achieved by removal of soil and, if so, what volume of soil would have to one must know or have estimates of the areas to be villages, for growing pandanus and breadfruit, for

Page 12

In order to to be removed to get an approximation of the amount of soil that would have bring about a given dose reduction, one needs to determine the three dimensional distribution of the radioactive contamination. Figure 3 shows the average Sr activities (pCi/gm) in soil samples collected to a be found in Appendix II of NVO-140. In addition to the 15 cm deep samples, radioactivity distribution as a function of depth (“profile samples”) was measured in fourteen locations on JANET. Data in Figs. B.8.2.a-n of Appendix II of NVO-140. indicates that, on the average, about 40 cm of from these prof~les are presented Inspection of these profiles soil would have to be removed “ to reduce the activity in the top 2 cm layer by a factor of 10. In addition, as the depth increases the slope of the activity-vs-depth curve tends to decrease, i.e., the activity levels do not go to zero, even at depths greater In an attempt to shows pertinent data for . quantify this distribution and obtain an approximation of for calculational purposes, 90Sr and 137Cs data for each of the fourteen profile samples have been reproduced in Tables 6 and 7. The average values for Sr for each sampling depth are plotted in Fig. 4, It is apparent that from the surface to about 30 cm the Sr specific activity is decreasing with a “soil half thickness” of 8.4 cm, while in the 30 to 85 cm depth range the half thickness increases to 22 cm. The levels do not get as low as those found on the southern islands (10.5 pCi/”gm) at any depth down to 180 cm. Those profile samples which lie in or closest to the subsistence agriculture areas of Figure 2 have been averaged and plotted in Fig. 5. In this set, the half thickness is only 4 cm from the surface to 10 cm, but increases to 25.5 cm in the 10 to 85 cm depth range. Similar treatment of the 137Cs data is plotted in Figs. 6 and 7. In Fig. 6, where all samples are

Page 13

averaged, the half thickness is 4.5 cm down to about 10 cm, and 12 cm from 10 to 85 cm. Levels equal to those found on the southern islands (’LO.2pCi/gm) are found at depths below about 100 cm. In Fig. 7, the subsistence agriculture case gives a half thickness of 2.7 cm down to 10 cm, and 17.8 cm from 10 to Sr and ’37Cs it is apparent that the profile averaged over all samples is more conservative than is the profile for subsistence agricultural areas for estimating has used Figs. 4 and to removal of soil. In making these in mind; first, that the effects of soil removal; therefore, t~e Task Group 6 for estimating dose reductions that might occur due dose reduction approximations, …