ADDENDUMTO TECH NOTE 2.1: DETERMINATION OF THE PLUTONIUM TO AMERICIUM RATIO IN SOIL SAMPLES FROM IRENE DOE/ERSP TECH NOTE NO. 2.1-B DATED: 25 July 1979 AUTHOR: Madaline Barnes, DRI In examining chemistry results for samples taken from soil more than 20 em below the original surface of Irene it became clear the TRU/Am ratio was changing as a function of depth. Some of the samples were taken after recontouring of the excision area near 13-N-1 and 12-N-2; others were Samples analyzed as part of the TRU subsurface investigation process triggered by FPDB sample results. (See Tech Note 18). Accurate TRU/Am ratios were needed to determine whether or not cleanup criteria had been met on Irene. Ratio information was therefore checked for every area affected by excision, recontouring or backfill. Also, the original TRU/Am ratios were estimated by the means of sample ratios. The characteristics of the data, explained in Tech Note 2.2-A, are such that the ratio of sample meansis a more appropriate estimator. The original soil sample data were used to compute the ratios of means, and these revised estimates were used for all areas not affected by soil moving. Table B-2-2 summarizes the original and revised ratio estimates and errors, Except as discussed below, the boundaries between areas with different ratios were not altered. In the region around 13-N-1, 12-N-2 and 14-N-1, the post-cleanup ratio was clearly different than any of the values in Table B-2-2. There were sufficient samples from this area to estimate a separate ratio. The post-lift ratio at 9-S-3 was the same as this region, and was included in the estimate. The ratio from the corresponding depth at 9-S-1 could also have been included in this group of samples, but was not because no soil was excised from 9-S-1. (Ratios in this group were computed using 24l4m from chemistry because gamma results were 12-N-2 - an analyzer problem is suspected. All others use 2414m from ratio data from 10-N-1 and 7-S-3 were about the same as the pre-lift west ratio at 6-S-2 was the same as the pre-lift central area ratio. Table B-2-3 erratic for 13-N-2 and gamma scan.) Post-lift area ratio. The post-lift summarizes the post-lift ratio information, The estimated ratio and error for the 14-N-1/13-N-1/12-N-2 region is 7.92 + 1.34, For the final post-cleanup TRU estimates, the boundaries between areas with different ratios were left basically the same. Corresponding revised ratios from Table B-2-2 were applied to data in each area, The new ratio estimated for the 14-N-1/13-N-1/12-N-2 region was applied to all data from the shaded area in Figure B-2-4. The shading includes all the area affected by lifting and recontouring in that vicinity. The new ratio was also applied to 9-S-3 post-lift, but was used at 14-N-1 only for post-lift data before backfilling. The backfill material came from the lagoon end of the 8-row, which is in the west region. Therefore, the west area ratio 11.27 was applied to post-backfill data at 14-N-1. Table B-2-2. TRU/Am Ratios for Irene Area Original Estimates Ratio Error Revised Estimates Ratio Error* East Central West 4.12 6.50 11.13 4.06 6.41 11.27 tn ’ 0.53 1.20 1.70 . : . 0.41 1.03 1.09 . Due to a programming error, the standard deviation reported here is overestimated. B-2-9