7.5.3 Pearl Background Island Pearl (Marshallese: Lujor) is one of the larger of the northeastern islands with an area of 22 hectares (ha). The soil is very sandy and the plant cover was moderate to heavy before any cleanup. Pearl was the site for one nuclear test event, Inca, which was located in the middle of the western quarter of the island as shown in Figure 7-84. Because of this event plus 12 other surrounding events, Pearl ranks sixth among the islands in the Atoll in total H + 1 hour exposure rate with 4,329 R/h A large quantity of debris including blocks of concrete remained on this island from the Inca event. There were no known or suspected burial sites on Pear. However, because of the surface ground zero on the island, it was possidle that some post-shot operations covered contaminated soil or debris. 1972 Survey Results In the 1972 survey, soil samples were collected at 53 sites on Pearl along with a few vegetation and animal samples. Of these sites, 45 were 0-15 em core samples, 5 were 0-35 cm samples, and 3 were 0-65 em profiles. Most of the profiles showed either a steady or steep decrease in 240 py, 137s, and 99Sr activities with increasing depth. The exception to this was a sample taken near the southeast end where the soil activities were more homogeneous with depth. The 0-15 em core sample results at five sites indicated a hot spot in the northwestern part of PearL As shown by Table 7-3, 239,240py concentrations on this island had a wide range of values and the highest values indicated that the agricultural criterion would not be met. Results for the 137Cs and 9%Sr data collected in 1972 are shown in Tables 7-1 and 7-2, respectively. Surface Characterization Pear] was initially measured with the IMP on a 50 m grid in October 1977 as shown in Figure 7-84*. Some 25 m grid points were also measured in the same time period in areas of higher Am concentration, These data were collected before any of the debris removal occurred and the only soil disturbance was due to the clearing of lanes for IMP access. Soil samples werefirst collected at five locations as shown in Figure 7-84 with two composites at three depths for a total of 30 samples. (See Section 4.2.1 for more information on soil sampling). Soil sample results from other islands showed very little 238pu, This was not the case for Pearl so the question arose whether this radioisotope would be included in the characterization of an island. Because of this uncertainty, two ratios were computed from the results of the initial five sampling locations for this island: 239,240by to 241 am and 238, 239,240 py to 24l am (see Tech Note 2.0). It was decided (See Section 2.2.3) to use TRU activity for island characterization, and new ratios were calculated for Pearl. These initial results indicated that there was more than one population of ratios on Pearl Nine new locations were sampled and three old locations were resampled. The results from these additional samples yielded three distinct ratios of TRU to “4/Am based on a cluster analysis as detailed in Tech Note 2.0-B. The ratios used in the initial characterization were 9.1 + 1.13 for locations within 150 m of Inca GZ, 7.80 + 2.18 for locations between 150 m and 350 m from Inca and 4.10 + 1.28 for locations more than 350 m from Inca, Figure 7-84 shows the boundaries for these ratios, Pearl was also the site for a brush attenuation experiment where 10 locations were first measured with the IMP in an area with the brush undisturbed except for the bulldozed lane. These same 10 locations were remeasured by the IMP after the brush in the IMP's field of view was removed by hand. (The area was hand cleared to minimize soil disturbance.) A brush correction factor was determined from these data to be 1.15 + 0.08. For the data used and a detailed write-up see Tech Note 1.0. This island also had some IMP measurements taken on a 25 m grid in two areas of higher 14m concentration. One such area in the northern part of the island was chosen because the aerial survey (Section 3.1) indicated elevated *41Am concentrations and the other area in the southern part of the island showed high 241 ar activity in both IMP and soil sample results. This *As map shows, the grid was not true north-south, 305