7.4 NORTHEAST ISLANDS 7.4.1 Kate Background Island Kate (Marshallese: Mijikadrek) has an area of 6.5 hectares (ha) and is the northernmost in the Before any chain of islands southeast of Janet, forming the northeastern quadrant of the Atoll. cleanup, the island was sparsely vegetated along the lagoon side and over a portion of the interior, while the rest of the island was covered with moderate vegetation. The soil is loose and sandy. Many test structures and scientific stations were located on Kate, and several remained until the cleanup. These were removed during the cleanup along with other metal debris and rubbie. Some soil disturbance may have occurred during the testing years because of the construction of these scientific stations. No ground zero sites were located on Kate and it ranks 15th amongthe islands inthe Atoll in total H + 1 hour exposure rate with 1,753 R/h. burials of radioactive material on this island. There were no known or suspected 1972 Survey During the 1972 survey, soil samples were taken at 26 sites on Kate and a few vegetation and animal samples were taken. Of the 26 soil sample locations, 23 were 0-15 em core samples and 3 were 0-65 em profile samples. One profile result showed a steady decrease in 239,240 py, 137¢g, and 90sp activities with increasing depth, one showed a homogeneous distribution of low activities and one showed an increase of activities to 20 ecm but a steady decrease below that depth. Overall, the results indicated no elevated subsurface activity would be expected. Tables 7-1, 7-2 and 7-3 give the 0-15 em summaryresults for 137s, 90sp and 239,2 Opu, respectively, for data collected in 1972. Characterization Kate was initially measured with the IMP in March 1978 on a 50 m grid. To determine a TRU to 41am ratio, soil samples were collected on 28 February 1978 at five locations with two composites at three depths for a total of 30 samples. (See Section 4.2.1 for more information on soil sampling.) A ratio of 2.69 + 0.03 was estimated using the soil sample results (see Tech Note 2.10). Both IMP and soil sample locations are shown in Figure 7-25. Using the ratio estimated and the 24lam IMP values, TRU numbers were calculated. These TRU values were used to compute the kriging estimates and 0.5 s upper bounds, where s is the standard deviation of the kriging error (see Section 5.1). The 0.5 s upper bound on the highest 0.25 hectares (ha) average TRU estimate was 40.3 pCi/g based on original data. (See Tech Note 23 for discussion of original versus final data.) However, these results were based on IMP data collected before debris removal, and as previously mentioned, Kate was the site of many test structures. Therefore, it was Suspected that debris removal, which caused substantial soil dusturbance, may have changed the surface radiological condition of the island. Kate was remeasured with the IMP on the same 50 m grid in March 1979 after the completion of the debris removal activities. Additional surface soil samples were collected at the same five locations previously sampled with four composites at each location for a total of 20 samples. (The soil sampling procedure had changed for a short time period during the cleanup.) A ratio of 2.74 was calculated from these new soil sample results which was not significantly different from the ratio originally estimated, thus the old ratio was used to compute TRU values. Estimates and 0.5 s upper bounds based on the remeasurement data were calculated using the kriging technique. It was obvious from the data that some soil mixing had occurred. After debris removal, the 0.5 s upper bound on the highest 0.25 hectares (ha) TRU estimate was 33.5 pCi/g based on original data. Figure 7-26 shows the isopleths of TRU activity computed from the final IMP data. Table 7-5 gives island averages for computed TRU, 137 gs and 69Co activities for the final IMP data. 232