The grid spacing of 25 m for IMP sampling rather than the usual 50 m spacing was chosen because Clara is so narrow the larger spacing would have resulted in too few samples to fit a variogram and make estimates. With data at 25 m spacing, estimates are based on averages of adjacent data rather than kriging. Figure 7-17 shows the isopleths of final TRU activity based on the IMP data. (See Tech Note 23 for a discussion of original versus final data.) Table 7-4 summarizes island average TRU, 137C5 and §9Co activity from IMP data. Severe soil disturbance from lane-cutting activities may have affected the IMP data, particularly along the baseline. The effect is unlikely to have been even as much as a 10% attenuation in the reading (see Tech Note 4.0), therefore no correction was made. The island surface was severely disturbed again, after the surface survey was complete, when the one scientific station left from o nm Al oy Gn n ~~ o —-—— 0 3° nO testing activities was removed with high explosives. The surface characterization was not affected by this, but it was a factor in later subsurface investigations. BL — si — 40 $2— Le $3-— $4-—_ APPROXIMATE HIGH TIDE, |972 $5-——_ $6 — $7—— LAGOON CLARA - KIRUNU 2am FIGURE 7-17. ISOPLETHS ON FINAL ESTIMATED SURFACE TRU ACTIVITY IN pCi/g FOR ISLAND CLARA 224