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

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TABLE OF CONTENTS TASK GROUP STATEMENT CONCERNING THE THE TASK GROUP ASSESSMENT OF D.OSES AND THE RESULTS OF ALTERNATIVE E CORRECTIVE ACTIONS TASK GROUP OBSERVATIONS AND CONC LGSIONS REPORT, SUMMARY OF FINDINTGS CHAPTER SUSPENDED PLUTONIUM IN AIR AND PLUTGNIUhl APPENDm IV, ANNUAL BONE AND WHOLE-BODY DOSES

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On September 7, 1972, the Atomic Energy Commission (AEC) agreed to provide radiological criteria for cleanup and rehabilit.at<on of Enewetak Atoll to the Department of Defense (DOD) and to the Department of Interior “ (DOI) . AZC also agreed to conduct a comprehensive radiolo~ical survey. The purpose of the survey was to gain a sufficient understanding of the total radiological environment of Enewetzl. Atoll to support judgment as to whether all or any part of the Atoll can safety be reinhabited and, if so, to describe cleanup actions to be taken and any constraints. Radiological survey field operations were conducted between riid-Octcber 1972 and nid-~ebruary 1973. Smples tdien in the field have been analy:!ed and complete results of the survey have been published i-s a Nevada Operations Office document (iJ\’O-140), Enevetak Radiclo:;icd Survey, Vols. 1, 11, III. An abstract of NVO-140 is presented in Ap~endix I of this report, and the “Surmary of Findings” chapter is reproduced here in Appendix II. In July 1973, a Task Group was established to reviw t!le Survey fim?in~s and to prepare cleanup md rehabilitation recommendations foz considcra:icm by the Commission. Members Advisors and consultants to liaison representatives from Dlii\, EPA, and DO1 participated in Task Group The job of the Task Group ic to recommend radiological criteria for cleanup and rehabilitation o,r lhc~.etak Atoll and to recommend those rer.cz!ial

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measures and actions needed to reduce exposures of the Enewetak people to levels within these criteria , and to keep exposures as low as practicable. The Tzsk Group, advisors, and consultants have carefully reviewed the AEC Radiological Survey results; current information on the life style, diet, and rehabilitation preferences of the Enewetak people; applicable radiatios protection guidance established by various national and internatior.al Radiat:on Standards bodies; and current laws and regulations pertaining to dispcsal ofradioactive waste materials. The recommendations that were developed are those that, in the judgment of the Task Croup, advisors, and consultants, are most appropriate fox the U.S. Government to talce to provide a radiologically acceptable envircmrwnt for tile Ikewetak people considerin~ they will be long-terfi residents on the After thorough review of the Ikdiological Survey wAcs the following observations: o The survey provides an exceptionally complete Report., the Taslc data base for estimating radiation doses. It includes tile results of m aerial fiarzna radiation survey of land area plus radiochenical data from the analysis of over 4500 samples of air, soil, se~?imnt, water, and marine and land aninals.

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e The Survey report, plus the Master Plan for Rehabilitation and reand up-to-date assessment of the likely living patterns and diet of the Enewetak people. l “Several important components of the Enewetakese now available on the atoll, or are available in diet axe either not quantities which, are small conpared to available at all, new; pandanus and the needs of the people. Pigs and chickens are not but will be reintrod~ced. No breadfruit is growing tacca are growing only in scattered locations; and coconut is growing in quantity only on the southern islands. 3readfruit, pandanus, tacca, and coconut must be planted and will be~,in to produce crops after about ei@Jt years. Radiation dose estimates for these foods have had to be based on correlations with plants and anfmls ~ow present on the ztnll and c?. inferences drawn from earlier surveys on Likini zu~d Rcnfiehp. T1/eTc are many ‘data points, and these correlations provide the best. m~thoc! currently available for estimating internal exposures. l{evertheless, the method is not as reliable as direct neasurenent of the foods produced in the areas of concern. l Air samplin~ at Lne~*etak, accor.plished largely during a threz week period in Decenber 1972 on unin>abitcc! northern islands, showed extremely lo~- levels of airborne radioactivity. coi3- *“Ihewetak Atoll Master Plan for Island Rehabilitation and Resettlement,”

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prehensive air sanpling during 12” consecutive months under conditions closely approximating human habitation and soil disturbance would provide more accurate data on which to base l The Knewetak People principal source of advise that catchment rainwater is the customary 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 JLMIT in 1971. A t?lorou~h lens water sanpling, analysis, and assessment program requires sa.apling throu~il a full rain-dry season cycle, 12 consecutive months at a Dinim.um. Arrangements for sam?ling fresh water lenses are e It is the opinion of the Task Group that the results of aaditicnal air sanpling or lens water sampling probably would not significantly change the dose estinates in l\TO-140 nor ch~nge the recoriencl:*- tions of this Task Group. A review of the radiation protection standards and guides considered h’? the Task Croup to be applicable to Enewetali is presented in Appendix 111. This review indicates that the numerical standards and radiation prstectiGn philosophy of both national and international standards bodies are sirilar.

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Summarizing that appendix, the specific guidance and criteria used by the Task Group in its assessment o.= the data and recommended for cleanup and rehabilitation of the atoll, are as follows: G The population dose to the lkewetak people should be kept to the minitim practicable level. @ A value of 50 percent of the Federal Radiation Council (FRC) Radiation Protection Guides (?J%’s) for individuals is rcconmended for the criteria to be used in evaluating the various exposure reduction options considerin~ that such exposures cannot nov* be The follo:~in~ values apply: Whole body and bone marrow - 0.25 Rem/yr o The guide for gonadal exposure of the popula~ion shmlti. be - 4 remz in 30 years. e The.guidance for 239 Pu in soil s!~ould be the following:’: of soil - corrective action required. ~ese values are recommerided for use in cleanup of Enewetak Atoll only.

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The Task Group approach for the radiolo~ica.1 cleanup and rehabication of Enewetak was to consider a number of alternatives for exposure reduction thzt may be feasible. hasi( the procedure Involved four steps: a Assessment of doses for ~ population Ii\*ing on the atoli in its current radiological condition. e Assessment of dme reductions tl~at might be expected clue to rnodific tion of the diet. v Assessment of dose reductions that might be expected due to removal population doses on che atoll in its current radialo@cal condition for si living patterns chcsen to be nest representative of the Znewetnk pco?le’s desired l~f.e style after they return. In addition, dose esti~iitcs are K-M: fGr each of these liv~ng patterns for each of the following corrective acl o Gravel the village area and plow the villa~e island. Q Import pandanus and breadfruit from the sotithern islands (AL’/IllKEI’Ri) for inhahitancs of the northern islands. e Import pandanus, breadfruit, coconut and tacca from the southern Q Import pandanus, breadfruit, coconut, tacca, and domestic mat f~ the scmthern islands.

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The estimates for 30 year whole bociy” 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,” achives a minimal reduction in radiation exposure of whole body and bone for all living patterns$ and those living on JN??ZT would have to import most foods to avoid exceeding a whole body exposure of 4 reins in 30 years. Population dose guidelines used by the Task Group include annual dose rates as well as 30 year intergr81s for gezetis doses. Tables 3 aiid 4 show estimates of the “inaxfmumannual whole body In considczing the reduction in exposure renoval of contanlnated soil, the Task Group has to reduce internal exposures must be conf.irned throu[;h analysis of test In its assessment of dose reductions that mi~,ht be possible removal of contaminated soil, the Task Group posed the follok’iny, “Given the dose estimates of Tables 1-4, and the dcse reductions be expected due to modifications of the diet, can equivalent dose reductions be achieved by remcval of soil and, if SOS what volumz of soil woald have tc be removed froz cmtaminatcd is18nds”? In order to address this questim *A detailed description of the calculations leadln~ to the estimates in Tables 3 and 4 is given in Appendix 117. *Whe Task Group does not favor soil removal as a dependable exposure reductiori action. Howvcr, such action is re.vieved Report in order to present a ccmplete picture oi’ the various in the Task Growp

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one must know or have estimates of the areas to be used for housing and villages, for growing panda~us and breadfruit, for growing coconut, and for raising domestic animals. Figure 1 shows the Ihevetak Atoll Land We Plaxn as presented in the Enewetak Atoll Haster Plan. Of the northern islands only Enjebi (JANEI) is expected to be a residence and agricultural island. Aej (OLIVE), Lujor (PEARL), to be used as In order to to be renoved to LUCY, IIMY, lMliCY, and lJIL~) as food gathering and picnic the land use plan for lkrjebi Island (JMKT) , includtn$ get an approximaticm of the amount of soil that would ;lave bring about a given dose reduction, one needs to dete~lfne the three dimensional distribution of the radioactive contaiiination. ~i~u=e ~ shows the average depth of 15 cm on 90 Sr activities (pCi/Cm) in soil samples collected to a Appendix II of WO--l40. In addition to the 15 cm deep sanples, radioactivity distribution as a function of depth (“profile sanples”) was measured in fourteen locations on .TAIJH’. l)ata frcm these profiles arc presented in Figs. B.8.2.a-n of Appendix 11 of lNO-140. Inspection of these profiles indicztes that, on the average, about 40 cm of soil would have to be removed to reduce the activity in the top 2 cm Iayer.by a factor of 10. In addition,

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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, Table 5 sh&s pertinent data for . even at depths greater In an attempt to quantify this distribution and obtain an approximation of fourteen profile samples have been re~roduced in Tables 6 and 7. The average values for Sr for each sampling de~th are plotted in Fig. 4. It is apparmt from the surface to about 30 cm the 90 Sr specific activity is decrczsing with a “soil half thickness” of 8.4 cm, while in the 30 to 85 CIAdepth range the half thickness increases to 22 cn. The levels to not xet as low as those found on the southern islands (%0.5 pCi/gn) at any depth down to 180 cm. ThQsc profile samples which lie in or clcsest tc the subsistence agriculture areas thickness is only 4 cm from tl~e surface to 10 cm. huc increases to 25.5 cu in the 10 to 85 cm depth range. Similar treatment of the i37 Cs dat:. is plotted in Figs. 6 and 7. In Fig. 6, where z1l ~aples 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 (6.0.2 pCi/gn) arc found at depths below about 100 cn. In Fig. 7, the subsistence agriculture case For botl] 90 Sr and 137 Cs it is apparent that the profile avera~ed over all samples is more consemative than is the profile for subsistence a~ricultural areas for estimating the affects of soil rcnoval: therefore the Task Croup has used Figs. 4 and 6 for estima~ing dose reductions that tight occur due to removal of soil.

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In making these dose reduction approximations, one must keep two things in mind; first, that the NVO-140 does estimates for terrestrial foods grown I an island such as JANET are based on correlations between certain indicator average soil concentrations in the 0-15 cm samples (Fig= 3) sir;ce as pandanus and breadfruit were not found on .JAN2T and, second, concentrations are averaged over the 0-15 cm depth of Figs. 4 anc Estimates of dose reductions to be expected due to removal of soil to a give depth, therefore, require an estimate of the ratio of the averafie concenrra! of the nuclides of concern in the 0-15 cm depth of the newly ex~osed surfact to that for the surface which is present now. This approach does not cons~., che radioactivity in the soils deeper than 15 cm which may be ii~portant, particularly’for plants with roots that penetrate deeply into the soil. ‘la increment from. the present surface down to 105 cm as derived from FiCs. 4 c These estinatcs indicate, for example, thct removal of 15 cm of soil nk>y r: the terrestrial food dose due to 90 Sr by a factor of 3.3 and that due to 137 (k by 3.2. however, such reduction ray or may not be actually achieved There is no experience to support these reduction levels. Using the data of Table 8, one nay assess the dose reductions that mi occur due to sycific cleanup actions on J~TLT. Table 9 shows the doses that might occur due to seven different conditions. Case D represents the contributors to the 80 Rem bone dose of Table 2 using values for . 137 Cs averaged over all of JAIJET. Case D1 indicates that if subsistence agriculture is limited to shore) the Sr and resulting 30 yr hone dose the area shown in Fig. 2 levels may be reduced to

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137 Cs (4.5 cm) in the residential areas has little effect since that action influences only the external gamma dose. Removal of successive 15 cm lzyers of soil in the subsistence agricultural areas, however, may reduce the bone dose by si~ificant amounts. Removal of the top 15 cm layer, may reduce the 30 year bone dose from 57 P.em to 19 Rem~ while additional 15 cm may brin~ the dose down to 10.7 Item. Since soil renoval-vs-bsne dose reduction would possibly removal of an be most effective for pandanus and breadfruit, a variation on the estimates of Table 9 may be obtained by preferentially stripping soil in areas where these trees are to be grown. grown in the of soil have For case D-1, for example, if pandanus and breadfruit are subsistence agricultural areas only in sections from which 15 cm been renoved, the resulting bone dose may drop frcm 57 Rem to the dcse may drop to 23.7 k-m. achieved is through outside the atoll. The maxim.. dose reduction that can be importation of clean soil from the southern isiantis or from 90 Sr concentrations in the average profil?(’rable 6) do not get as 10V as those on the southern islands even at a depth of 180 Cm. To achieve this moximum effect, however, sufficient clean soil has to be imported to encompass the entire root systen …