COMPUTATION OF TOTAL TRU ACTIVITY REMOVED FROM THE HUSTEAD AREA OF ISLAND SALLY DOE/ERSP TECH NOTENO.10.1 DATED: 28 July 1978 AUTHOR: M. G. Barnes, DRI The total activity removed from the Hustead area was computed using TRU values computed from IMP survey readings taken before and after soil excision. Soil gradient models were fitted separately to the portion having subsurface contamination exceeding 80 pCi/g TRU, and to the remainder of the area. Soil profile data for the area without subsurface contamination are shown in Figure B-10-5. The gradient is exponential, with before excision average of 64.7 pCi/g TRU, and after excision average 21.5 pCi/g TRU. Then, using the notation of Tech Note 10.0, k = 64.7 ky = 21.5 ky _= 0,332 — k 1 ed = 0.907 The average TRU concentration in the soil removed was therefore 64.7 x 0.907(1-0.332) = 39.2 pCi/g TRU. The total volume of soil excised from this section was 460 cubic yards, so the total activity removed was Soil profile data for the area with subsurface contamination are shown in Figure B-10-6. The gradient rises to a peak at 20 cm and drops off exponentially below 20 em. The rise was modelled as linear, since not enough data are available to fit any other model. It was assumed that the IMP readings after the first lift represent the peak concentration, and the total excision depth was 40 em (2 lifts). Then the average concentration in soil removed was 0.5(56.8 + 86.5) + 0.5(86.5 roy 39.2 x 460 x 1.185 x 10-6 = 0.02 Ci. x 1.1371(1-0.4150)) = 64.6 pCi/g TRU. The volume of soil removed from this section was 740 cubic yards, so the total activity removed was 64.6 x 740 x 1.185 x 10-6 = 0.06 Ci. The total activity removed from the Hustead area,* as calculated by these methods, would be: 0.02 Ci + 0.06 Ci = 0.08 Ci. were om *See Editor's Note on page B-10-4. B-10-9