it unsuitable for habitation, agriculture or food-gathering. Tables 7-1, 7-2 and 7-3 summarize the

3%Cs, 90sr and 239,240 py results, respectively, for the 0-15 em average; island average results for

other profile ranges are shown below:
0-5 em

oS pCi/g
137¢5, pCi/g

34.1
6.10

0-40 cm

38.2
5.8

0-60 cm

Total Samples

36.6
5.4

90
317

When the FPDB samples were analyzed for 241 4m, eleven locations were discovered to have one or
more samples with TRU activity, possibly exceeding 160 pCi/g. After additional chemical analysis
to check the ratio of TRU to 2 lam, seven of the locations were confirmed to have TRU activity
exceeding 160 pCi/g. The earlier subsurface investigations, sampling only 5 em of each 20 cm
interval, had failed to find these locations, while the FPDB method included samples from the

entire 0-60 em profile. The FPDB samples also yielded more specific information about the depth

of subsurface activity than the auger core samples, and this information was incorporated in the

followup sampling design.

Tech Note 18 describes the sampling design that was used to investigate the seven locations with
elevated subsurface activity. The new design produced better boundary definition with fewer
samples, resulting in a substantial savings in time and effort. The locations investigated with this
method, shown in Figures 7-55 to 7-61 respectively, were: 9-S-1, 12-N-1, 6-S-2, 7-S-3, 10-N-I and

14-N-1. After two iterations of soil sampling, it was clear that while 9-S-1 and 12-N-1 would not
require cleanup, soil removal was necessary at all the other locations. Horizontal boundaries for the

five soil excision areas were determined using the new method, but depths of each excision were

based on standard sidewall sampling (Section 4.2.1). The investigation lasted from 3 to 16 June
1979, and soil lifts began 13 June, while two sites were still being sampled; the initial lifts were

completed June 19. The excavations were soil sampled 27 June, and only 14-N-1 required more soil
removal. Handheld instruments were used to direct the final lift at 14-N-l. The IMP remeasured
all the locations, confirming that no 0.0625 hectare exceeded the 160 pCi/g criterion for TRU
activity. Because it was too deep to leave open, the excavation at 14-N-1 was backfilled with clean

beach sand.

After the cleanup operations were completed, IMP measurements showed no 0.5

hectare had average TRU activity greater than 80 pCi/g.

This phase of subsurface cleanup ended 14 July 1979, after an estimated 1,350 cubic meters (1,780

cubic yards) of soil, containing an estimated 0.41 Ci of TRU activity, were removed.

The results of the FPDB sampling for 0-40 em profile means of 137s and 9%Sp for Irene are shown

in Figures 7-62 and 7-63, respectively. Only the main island is included because the Helen spit was
not sampled.
Final Characterization

Following the last cleanup operations on Irene, all the chemical analysis results for soil were

compiled to arrive at a final set of ratio of TRU to 241am.

Details of the computations and data

used are in Tech Note 2.1-B. Four ratios were used for the final TRU estimates: 4.06 + 0.21 for the
east end, 6.41 + 0.43 for the central area, 11.27 + 0.38 for the west end “(except
the
14-N-1/13-N-1/12-N-2 excision areas), and 7.92 + 0.44for the 14-N-1/13-N-1/12-N-2 excision

areas. The boundaries for each ratio population are shown in Figure 7-64, along with isopleths on

the post-cleanup surface TRU eee
(based on final data). Table 7-4 summarizes the post-cleanup
status of Irene for TRU, 37Cs and
©9Co from IMP data. Based on final data, one 0.5 hectare had

average TRU activity imag to be 87.7 pCi/g; all other 0.5 hectare averages were less than 80
pCi/g.

The island average transuranics value reported in the Certification is 31 pCi/gm for surface soil,

and the transuranics classification is Agricultural.

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