Notes of a Meeting DR Gilbert Attended in Joe Deal's Office on July 29, 1976 Discussing Upcoming Enewetak Cleanup

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FOLDER we Wetak lq7~ DOCUMENT DOES NOT CONTAIN ECI Notes d a meeting Dr. Gilbert attended in Joe Deal’s office on July 29, 1976 discussing upcoming Enewetak cleanup.

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Additional Guidance Needed for Enewetak Cleanup of Pu Contaminated Soil 1. Over what area or areas should Pu-in-soil” measurements be averaged: what areas should the Pu cleanup criteria, 40 pCi/g and 400 pC-i/g, .<,, 3. Lookin8 at past survey results compared with the cle”~nup criteria, which islands need cleanup? What levels of assu;ance that the criteria are met without clea~up are reasonable and attainable? ‘4. For certification Of islands for which cleanup of P.uhas been b. How are the data to be evaluated?- C. What are goals that are likely to bz attainable in terms of the assurance that can be give~ that the cleanup criteria have 5. For cleanup operations, is there some optimum combination of In-Situ, soil sampling, and “wet chemistry meastirements that yields the most relevant information to guide contaminated soil removal -at the least cost? Can a generalized approach be developed for use with all islands or should guidance be derived for the known conditicm; of each island

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Table 13. Number of sample locationson each island. Approx Assumed No. ofsample Iocatinns

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q2JifJ- The radioactivityseems to be fairly ~iclidr Mean Range homogeneously distributedthroughout the 137C5 36 5.6-141 struction activities,,such as the building :;~pu 12 3.9-68 of an a;rstripalong the center of the Coco 5.9 1.4-33 island and large-scale earth grading at Mean Range Mean Range Mean Range Mean Range (I.y:\];- Because of the complex distributionof activitieson Nort}~ernY\~ONN12 no sinclemean value for an isotoDe can be used for the island as a whole witll-

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Table 16. Encwetak soildata, southern islands (pCi/g in top 15 cm). iMean Range Mean Range Nlean Hange Mean Range aSAM, TOM, URIAH, VAN, ALVIN, BRUCE, CLYDE, REX, WALT, GLENN, HENRY, IRWIN, JAMES and KEITH. the northeastern end, took place during tivehomogeneity is also supported by the results of the aerial survey. The activitiesas a functionof depth, obtained from Locations 24, 26, and 100 within the island’sinterior,follow the general rule of a rapid decrease in activ~ itywithin the firstfew centimeters of the and then leveloff to become almost tion 100). Profile samples collectedat Locations 23 and 25, which are on or near the beaches, display essentially the photographs, this island is so heavily vegetatedthat itwas almost impossible to penetrate. The only exception is”the northeast corner of the island, which is relativelyopen with sparse vegetation. Most of the soilsamples were collected withinthe densely vegetated areas, ;vith a few obtainedwithin the sparsely vege - tated northeast corner. The following nuclide Llean Range Areas of dense vegetation Areas of sparse ve~etation The mean activitiesexhibitedby the samples from the northeast corner are roughly a factorof three smaller than those from the‘remainder of the iskmd. Since only a few samples were collected within the corner area,”the factorof three may or may not reflectthe true differencein the mean values. The aerial survey resultsdo not reflectthis

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Pacific Northwest Laboratories Defense Nuclear Agency ,, Kirtland Air Force Base, NM 87115 Enclosed are the 239-240 Pu in soil contours Dr. Pam Doctor and I obtained using the data you sent us that were collected at random soil locations on the island of Enjebi (Janet) Enewetak Atoll in 1972. The enclosure labeled “A” gives estimated contours in units of pCi/gram; in addition, the location of data points are indicated by a cross. Three cont,our levels in loge scale are indicated; 2.08, 2.71 and 3.56. These are rounded from actual contour levels of 2.079442, 2.70805, and 3.555348, which when antilogs are taken, correspond to 8, 15, and 35 pCi/gram, respectively. The contours on the plot are in loge units since the contours were obtained on the logarithms of the data. The coordinates around the plot correspond to the North and East coordinate system you supplied with the data. Enclosure “B” !ives the same contour lines as “A” and in addition plots the value of the 2 9-240Pu soil concentrations (pCi/gram) at.collection locations. These are the data used to estimate the contours. Enclosure “C” is identical to “B” except that Pam has roughed in the shoreline of Enjebi and colored the four bancls of estimated concentrations (<8, 8-15, 15-35, >35 pCi/gram). The contour lines extending off the island should be ignored. The estimated contours were obtained using a nearest-neighbor estimation routine on the SURFACE II Graphics System developed by the Kansas Geological Survey. This system is described in “The SURFACE II Graphics System” by R. routines used were GRID and NEAR. The basic idea is to estimate 239-240Pu concentrations at equally spaced grid points over the island. The grid size used here was 100 feet. The estimate at each grid point was obtained as a weighted average of the eight nearest data points, where the data nearest

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to the grid point are assigned the highest weights. As mentioned above, the data were transformed to logarithms before any calculations were made. Once the grid estimates are obtained the desired contour lines are drawn automatically by linear interpolation between grid estimates. Me did not iterate on the r[!siduals to produce the enclosed contours. Iteration does not seem to be required for these data, i.e. the contours obtained after iterating would, in my judgement, be about the same as those given here. The 239-240 Pu data collected at O-5 cm and 0-10 cm increments were adjusted to correspond more closely to the 0-15 cm increments used at most sample locations. This was done by dividing the O-5 cm and 0-10 cm data by 1.88 and 1.26, respectively. The factor 1.88 is the median of the ratios of O-5 cm to 0-15 cm concentrations obtained from the profile samples on Enjebi. Similarly, 1.26 is the median ratio of the 0-10 cm to 0-15 cm concentrations, The O-5, 0-10, and 0-15 cm concentrations were weighted averages of concentrations obtained at O-2, 2-5, 5-10, and 10-15 cm, the weights being 2/15, 3/15, 5/15, and 5/15 respectively. This is the same weighting procedure you have been using. I have enclosed the revised list of soil Pu concentrations dated September 1976 which you sent Pam Doctor in your letter of October 8, 1976. These are the data we used except for the circled data which are for the O-5 or 0-10 cm samPles The data used for these values are indicated next to the circled concentration. Please note that the North coordinate for sample location 120 appears to be in error since this N-E location is off the island. Using Figure B.8.l.f as a guide I replaced N144480 with N144880 which puts the sample in about the right position according to the figure. Also we have switched the Pu concentrations for samples 89 and 90 and for 27 and 28 since the Am/Pu ratios then fall into line. Since samples 89 and 90 are spatially adjacent and 27 and 28 fairly near to each otiler I don’t think the contours would change much if we hadn’t switched those samples. Now concerning the interpretation of the contour maps: It appears that the computer contouring has done a reasonably good job of automatically estimatiis the lack of confidence statements associated with the contours. As I have noted in our phone conversations, the method of contouring we have used does not provide for estimating these confidence intervals. This is most,unfortunate since we are left with a pretty map with little to guide us concerning its accuracy. Ue should recall, also that these contours were drawn without knowledge of the locations of detonation points, wind patterns at time of detc~nation, and other “subjective” data that might possibly be useful in drawing contours. I think we need to seriously face the question of whether

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our automatic contouring result are an improvement over someone setting down and drawing contours by hand. What is needed are estimates of variability on the contour lines. One can get a feel fo~ the relative accuracy of some of the contours in certain parts of theisland by noting whether any data points are in the vicinity of the contour lines. In general, other things being constant, the more dense the data points, the more confident we can be of the placement of the contour lines. We have talked some about Kriging and how this technique can give estimates of confidence limits on contours if the data are adequate. I understand you have a copy of Dr. Delfiner’s report on his attempts to use Kriging to answer the question “Which hectares on Janet exceed an average Pu concentration of 40 pCi/g”? His overall conclusion was that “this question cannot be ans!fered on the basis of the present data”. He indicated that denser sampling vias required in order to identify the “structure” (trends around the GZ’S or across the island) of the data for spacings less than 50 meters. This structure must be identified before Kriging can be applied to the above question. Dr. Delfiner suggested that “the best that can be done is to calculate an undifferentiated global mean. This raises the question of whether more samples could be collected around the GZ areas and/or hot spots suggested by the present data before the cleanup crew gets underway next year. These samples might allow thestructure to be estimated so that Krigin could be applied. Of course, the use of In Situ devices for measuring 24 Am on the island is another approach for obtaining data for estimating the structure. If the In Situ devices are used, however, it is imperative that the resulting In Situ 241Am data be calibrated with Pu concentrations in soil by taking a large number of soil samples close to each other and in the area “read” by the detector. This would need to be repeated at several locations on the island. This should be done before the In Situ device is used to make cleanup decisions. Hope these comments and the enclosed plots are helpful. I’m sending copies to Tom McCall at ERDA and Bruce Church at NVO, also. Senior Research Scientist Copies with enclosures to

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Pacific Northwest Laboratories U.S. Energy Research and This letter is in response to your request for guidance on the number of samples required for the proposed clean-up survey on the Enewetak atoll. I begin with some general comments then discuss specifically the questions you distributed at the meeting in Joe Deal’s office orIJuly 29, 1976. There is also an ap endix to illustrate the computation of certain confidence limits using ?39-240pu soil data from the island of Janet. This letter has benefited from corrunentsand suggestions by other statisticians at BNN (Drs. Lee Eberhardt,’ Tony Olsen, and Pam Doctor). The number of samples will depend in part on how well the portable Ge(Li) counter performs in the field, i.e. on how accurately the Ge(Li) readings relate to the amount of plutonium in soil. It will also depend on the statistical design used in the field and on whether it is decided that a contour map of plutonium concentrations is a major goal or whether probability statements about mean concentrations are preferred. Contouring calls for a systematic (uniformly spaced) sampling scheme, while probability statements require random sampling within sub-areas of an island. Probably it would be desirable to use some kind of sequential sampling scheme, in which results of an initial set of samples are used to decide whether a given area should be (a) considered “clean” (below some standard level), (b) cleaned up, or (c) whether additional samples should be taken before a decision is made. Such a scheme is likely to require continued attention by someone with statistical training, but may be expected to reduce the amount of sampling required. If contouring is used, Dr. Delfiner of the Centre de Morphologic Mathematique, Fontainebleau, Fran’ce should be consulted on this question of the number of samples required. Dr. Delfiner is knowledgeable on “kriging” (a contouring method), and he may be helping Bruce Church set up the technique for use on the islands. We understand that arrangements are being made for Dr. Delfiner to be in Las Vegas for 3 weeks in October and again in November to install his kriging routine on REECO’S computer. . The question of whether In-Situ measurements, soil samples, or both should be used for deciding whether an area or island should be cleanedup requires further discussion. To answer this question we need to know

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whether In-Situ or soil sample data are more indicative of future health risk of inhabitants. Is long term health a function of an average (integrated) measure of exposure such as obtained by an In-Situ device, or is it more a function of peak plutonium concentrations from soil aliquots? Also, the use of In-Situ measurements in the cleanup determination implies we need to determine the relationship of these readings to soil concentrations. This can only be done under field conditions. I would suggest a number of In-Situ measurements be made at different locations. At each location the total soil scanned by the device should be carefully collected and mixed and a number of aliquots be analyzed for plutonium. In this way a calibration equation relating In-Situ and soil sample concentrations can be estimated. This will no doubt need to be repeated for different islands or portions of islands since the calibration relationship may not be the same for all areas. If the decision to cleanup is made primarily on the basis of In-Situ measurements then the calibration information is necessary in order to relate to the cleanup criteria which, presumably, will be stated in terms of plutonium concentrations in soil samples. This reflects a basic decision needed before a sampling plan is selected. If clean-up decisions are to be based on wet-chemistry determinationson soil samples then the In-Situ device may serve only as a means of reducing the number of analyses needed. In any case, we suppose some chemical determination will be required for calibration of the device. Let us assume that the In-Situ measurements are related linearly to the average Pu concentration in the surface soil scanned by the In-Situ device. For example, if the PuIM ratio is constant then the data should look something like a linear “average relationship” through the origin as indicated in the plot below.

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The variability in Pu concentrations would probably be greater for high In-Situ readings than for low readings (as indicated in the diagram). 1f% is the level of Pu in soil signifying clean-up, this corresponds to an average In-Situ reading Xl. But the data in the diagram indicates individual Pu readings considerably greater than Y for In-Situ reading Xl. ?Hence, if the In-Situ device is used to meet the c can-up criteria in terms of Pu concentrations, the level of In-Situ indicating clean-up should be less than Xl. One candidate is the value of the In-Situ measurement {X. in the diagram) such that the upper (one-sided) 95% confidence on average Pu concentration is Yo. An alterriative approach would be that level of In-Situ reading such that some large percent (P) of the …