Report by the AEC Task Group on Recommendations for Cleanup and Rehabilitation of Enewetak Atoll

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THE AEC TASK GROUP ON RECOMMENDATIONS P(3R CLEANUP AND REHABILITATION OF ENEWETAK ATOLL

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TABLE OF CONTENTS TASK GROUP STATEMENT CONCERNING THE RADIOLOGICAL SURVEY RESULTS RADIATION CRITERIA RECOMMENDED BY ASSESSMENT OF DOSES AND THE RESULTS OF ALTERNATIVE CORRECTIVE ACTIONS DISPOSAL OF CONTAMINATED MATERIAL TASK GROUP OBSERVATIONS AND CONCLUSIONS APPENDIX II, ENEWETAK IL4DIOLOGICAL SURVEY REPORT, SUMMARY OF FINDINGS CHAPTER SUSPENDED PLUTONIUM IN AIR AND PLUTONIUM APPENDIX IV, ANNUAL BONE AND WHOLE-BODY DOSES

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CLEANUP AND REHABILITATION OF IZNEWIZTAI(ATOLL provide radiological criteria for cleanup and rehabilitation of Enewetak Atoll to the Department of Defense (DOD) and to the Department of Interior (LIOI). 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 judgmen~as to whether all or any part of the fioll ~~~ty be reinhabited and, if so, to destribe ,cleanupactions to be taken atidany constraint%. 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 Radiologicd Survey, Vols. I, II, III. An abstract of NVO-140 is presented &r 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 A3iurveyfindings 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 “~Task Croup The job of the Task Group is to r[commend,radiological criteria for ‘] cleanup and rehabilitation of Enewetak Atoll and to recommend those reudial

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measures and actions needed co reduce,exposures of the Enewetak people to levels within these criteria. -to keep exposures as low as practicable. The Task Group, advisors, and consultants have carefully reviewed the AEC Radiological Survey results; current information on the life style, diet, and rehabilitation pzeierences of the Enewetak people; applicable radiation protection guidance established by various national and international ~adiation JtandardsAbodies; and current laws and regulations pertaining to disposal of radioactive waste materials. The recommendations that were developed are those that, in the judgment of the Task Group, advisors, and consultants, are most appropriate for the U.S. Government to take to provide a radiologically acceptable environment After thorough retiew of the Radiological Survey Report, the Task Group makes the following observations: l The survey provides an exceptionally complete data base for estimating radiation doses. It includes the results of an aerial.ganma radiation survey of land area plus radiochemical data from the analysis of over 4500 samples of air, $oil,.sediment, water, and marine and land animals.

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l The A?6rvey report, plus the Master Plan for Rehabilitation and resettlement of Ecewetak Atoll*, provide ~ 9 9 ~; ‘~ living patterns and diet of the Enewetak people. l Several important components of the Enewetakese diet are either nut now available on the atoll, or are available in quantities which are small compared to the needs of the people. Pigs and chickens are not available at all, but will be reintroduced. No breadfruit is growing now; pandanus and tacca are growing only in scattered locations; and coconut is growing in quantity only on the southern islands. Breadfruit, pandanus, tacca, and coconut must be planted and will begin LO produce crops after about eight 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 -thod currently available for estimating internal exposures. Nevertheless, the method is not as reliable as direct measurement of the foods produced in the areas of concern. l Air sampling at Enewetak, accomplished largely during a three week period in December 1972 on uninhabited northern islands, showed extremely low levels of airborne radioactivity. Com- *“Enewe’takAtoll Master Plan for Island Rehabilitation and (3 Vols.), Holmes and Naner, Inc., Nov. 1973.;..-,.’}‘,..-

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prehensive air s~piing during 12 consecutive months uiider conditions closely approximating human habitation and soil disturbance would provide more accurate data on which to base princfpal source of advise that catchment rainwater is the customary water for human consumption. Except in emergencies, water from underground lenses is not consuned. Samples of underground water were not obtained during the survey, and radiochemlcal 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 seascn cycle, a minimum. Arrangements for sampling 12 consecutive months at fresh water lenses are l It is the opinion of the Task Group that the results of additional air sampling or lens water sampling probably would not significantly change the dose estimates in NVO-140 nor change the recommendations of this Task Group. MDIATION 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.

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Summarizing that appendix, che 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: l The population dose to the Enewetak people should be kept to the mininum practicable level. l A value of 50 percent of the Federal Radiation Council (FRC) Radiation Protection Guides (RPG’s) for individuals is recommended for the criteria to be used in evaluating the varioua”~~osure,... ‘“\’ reduction options considering that such exposures cannot now be The following values apply: ,.. . The guide”-forgonadal exposure of the population should be - lY -See Appendix III for additional guidance.

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for individual and gonadal exposures are recommended as the criteria to be used in evaluating the various exposure radiation options. The numerical guidance therein should be reduced by the factors of 50% for indi~-idualexposure and 20% for ganadal 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: Whole body and bone marrow - 0.25 Rem/yr Gonads --------------------- 4 Rem in 30 yr

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ASSESSMENT OF DOSES AND THE RESULTS OF ALTERNATIVE CORRECTIVE ACTIONS The Task Group approach for development of judgments and recommendations for the radiological cleanup and rehabitation of Enewetak was to consider a number of alternatives for exposure reduction that may be feasible. Basically, the procedure involved four steps: l Assessment of doses for a population living on the atoll in its current radiological condition. l Assessment of dose reductions that might be expected due to modification of the diet. l Assessment of dose reductions that might be expected due to removal of contaminated soil. l Comparison of these dose assessment matrices with the population dose guidelines used by the Task Group. The Enewetak Radiological Survey ~port (NVO-140) contains estimates for desired life-style after they return.~ In addition, dose estimates are made for each of these living patterns for each of the following corrective actions: the village area and plow the village island. pandanus and breadfruit from the southern islands (ALVINfor inhabitants of the northern islands. pandanus, breadfruit, coconut and tacca from the southern l Import pandanus, breadfruit, coconut, tacca, and domestic meat from the southern islands.

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The estimates for 30 year whole body doses in the Survey Report are summarized in Table 1, and 30 year bone dose estimates are summarized in Table 2. Note that the option for “Gravel Village Area - Plow Village Island,” achi$es a minimal reduction in radiation exposure of whole body and bone for ail living patterns, and those living on JAi{ETwould have to import most foods to avoid exceeding a whole body exposure of 4 rema in 30 year>>Population dose guidelines used by the Task Group q“ include annual dose rates as well as 30 year integrals for genetic doses.d Tables 3 and 4 show estimates of the maximum annual whole body In considering the reduction in exposure that may be achievable through removal of contaminated soi2, the Task Group has taken the position that these predicted exposures are approximation+ only.. ,~e effectiveness of such actions to reduce internal exposuresAmust be confirmed through analysis of test ~z In its assessment of dose reductions that might be possible due to removal of contaminated soil, the Task Group posed the following questions: , and the dose reductions that can be expected due to / A can equivalent dose reductions be achieved by removal of soil and, if so, yhat volume of soil would have to ; be removed from contaminated islands”? In order to address this question ; -e Task Group does not favor soil removal as a dependable Report in order to present a complete picture of the various in the Task Group

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one must know or have escimaces of the areas to be villages, for growing pandanus and breadfruit, for raising domestic aninals. used for housing growing coconut, and for Figure 1 sham the Enewetak Atoll Land Use Plan as presented in the Enewetak Atoll Master Plan. of the northern islands o~ly Ihjebi (JMWr) ~ residence and agricultural island. Aej (oLIVE), Lujor (PEARL), to be used as In order to to be removed to agricultural islands, and the remainder (ALICE, BELLE, CLARA, KATE, LUCY, MARY, NANCY, and WILMA) as food gathering and picnic shows the land use plan for Enjebi Island (JANET), including (560,000 ft2, asstaningan average housing area to be 200’ a community center (200,000 ftz), subsistence agricultural ft2), and commercial agricultural areas (7,300,000 ftz). 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 depth of 15 cm on JANET. Similar figures for 137CS, 60Co, and 239Pu may be found i 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 from these profiles are presented in Figs. B.8.2.a-n of Appendix II of NVO-140. Inspection of these profiles indicates that, on the average, about 40 cm of soil would have to be’removed to reduce the activity in the top 2 cm layer by a factor of 10. In addition,

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as the depth increases rhe slope of the activity-vs-depth curve tends to decrease,i.e., the activity levels do not go to zero, even at depths greater than 100 cm. Table 5 shows pertinent data for Sr. In an attempt to quantify this distribution and obtain an approximation of 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 from the surface to about 30 cm the 90Sr 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~o not get as low as those found on the southern islands (%0.5 pCi/gm) at any depth down to 180 cm. Those profile samples which lia 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 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 (%0.2 pCi/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 85 cm. For both 90Sr and 137Cs it is apparent that the profile averaged over all samples is more conservative than is the profile for subsistence areas for estimating the ~ffects of soil removal: therefore the has used Figs. 4 and 6 for estimating dose reductions that might to removal of soil.

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In making &hese dose reduction approximations, one must keep two things in mind; first, that the NVO-140 doeu estimates for terrestrial foods grown on an island such as JANET are based on correlations between certain indicator plants and average soil concentrations in the 0-15 cm samples (Fig. 3) since foods such as pandanus and breadfruit were not found on JANET and, second, that these concentrations are averaged over the 0-15 cm depth of Figs. 4 and 6. Estimates of dose reductions to be expected due to removal of soil to a given depth, therefore, require an estimate of the ratio of the average concentration of the nuclides of concern in the 0-15 cm depth of the newly exposed surface to that for the surface which is present now. This approach does not consider the radioactivity in the soils deeper than 15 cm which may be important, particularly for plar.ts‘withroots that penetrate deeply into the soil. Table 3 presents these average concentrations and ratios for Sr and 137Cs for each 15 cm increment from the present surface down to 105 cm as derived from Figs. 4 and 6. These estimates indicate, for example, that removal of 15 cm of soil may reduce the terrestrial food dose due to 90Sr by a factor of 3.3 and that due to 137Cs by 3.2. However, such reduction may or may not be actually achieved. .,\$ Using the data of Table 8, one may assess the dose reductions that might occur due to specific cleanup actions on JANET. Table 9 show the doses that might occur due to seven different conditions. Case Dzrepresents the contributors to the 80 Rem bone dose of Table 2 using values for 90 Sr and 137Cs averaged over all of JANET. Case ~-{indicates that if subsistence agriculture is limited to the area shown in Fig. 2 shore) the Sr and 137Cs levels may resulting 30 yr bone dose becomes 57 be reduced to (i.e., along the lagoon such an extent that the

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of soil in cm) in the residential areas has little effect since that action only the external gamma dose. Removal of successive 15 cm layers the subsistence agricultural areas, however, may reduce the bone dose by significant amounts. Removal of may reduce the 30 year bone dose from 57 additional 15 cm may bring the dose down the top 15 cm layer, for example, Rem to 19 Rem, while removal of an Since soil removal-vs-bone dose reduction would possibly be most effective for pandanus and breadfruit, …