7.9 SOIL REMOVAL ISLANDS Those islands which were nuclear event ground zero (GZ) sites were the most severely affected by nuclear testing operations. A typical sequence of activities for a test included site preparation and construction of test-related structures. Then, after the event, monitoring devices would be recovered, some structures might be removed, contaminated materials were buried or removed, and the soil recontoured. The event itself might have destroyed vegetation, produced a tidal wave, and perhaps destroyed or rearranged the island surface, as well as leaving radioactive contamination on the island. In some cases, the damage extended to complete destruction. The Mike event left only a large crater in the reef where island Flora (Marshallese: Elugelab) had been. Island Gene (Marshallese: Teiteiripucchi) was damaged by several events, and eventually destroyed completely by the Koa event, which also left only a crater in the reef. The same series of events that destroyed Gene also destroyed most of island Helen and significantly altered island Edna. The small part of Helen still in existence has merged into a sandspit which extends westward from island Irene. There is also a crater on the western edge of Irene as a result of the Seminole event. Two similar craters at the north end of island Yvonne were made by the Lacrosse and Cactus events, The Cactus crater was filled with contaminated soil and debris that was removed from other locations during the cleanup, and a 25 ft high dome of soil/eement with a clean conerete cap was built atop the crater site. The original island of Ruby was almost completely destroyed by the George and Mohawk events; the remnants form the Cape Mixan area of island Sally and the island now known as Ruby. Because the present island is not representative of the original island, Ruby is discussed in Section 7.4 rather than as a ground zero island in this section. The ground zero islands discussed in this section are also the islands which required soil removal in the cleanup. The general approach to surface cleanup was to use the kriging method (see Section 5.1) on IMP data on a 50 m grid to determine the approximate area requiring soil removal. Then the boundary of the cleanup area would be refined by taking IMP measurements at 25 m intervals, which provided substantial coverage of the surface. After each soil lift, the entire area lifted would be remeasured at 25 m spacing and the lift-remeasure process was repeated, if necessary, until the applicable criterion was met. The standard procedures for surface soil sampling (see Section 4.2.1) were used for the ground zero islands. Multiple ratio of TRU to 241 am populations were present on all of these islands, so many more samples were taken than the minimum called for in the procedure. The maps accompanying the individual island reports show the boundaries between populations of ratios as determined from the soil sampling results. Subsurface soil sampling was conducted on all these islands using a variety of methods (see Section 6.9 for details) at all known or suspected burial areas. Suspected areas automatically included the immediate vicinity of all GZ's because it was commonpractice for event craters to be used as burial sites for contaminated material. Other areas were investigated based on information in as-built drawings, operations reports, verbal reports by nuclear testing participants, and on data from the 1972 survey. The suspected burial areas are shown on the individual island maps, and results of subsurface sampling are included in the island reports that follow. For all of the ground zero islands except Yvonne, the island report includes the pre-cleanup surface TRU characterization and isopleths on the post-cleanup surface TRU. Also ineluded on all but Yvonne are isopleths on the post-cleanup 0-40 em average 187Cs and 90sr activities, based on data from the Fission Product Data Base (FPDB) program. Only the final TRU isopleths are given for Yvonne because only part of the island was measured with the IMP before cleanup, and only southern Yvonne was included in FPDB sampling. Results from the 1972 survey and the FPDB program are summarized for all the islands in Tables 7-1, 7-2 and 7-3. Table 7-5 summarizes results of IMP measurement made during the cleanup, and Table 7-6 gives the volume of soil excised and the TRU activity removed during the cleanup. 260