7.5.5 Yvonne Background Island Yvonne (Marshallese: Runit), the most northerly of the southern island grouping, is one of the largest islands in the Atoll, having an area of 37.0 hectares (ha). Yvonne is a long, slender island with mostly firm soil, and was once moderately to heavily vegetated. However, nuclear testing activities denuded it and regrowth has been limited by subsequent activities. The northern and southern parts of the island have quite different histories of contamination from nuclear tests. Because of this, and the size and shape of Yvonne, the island has been divided into two sections at Hardtack Station 1310, a large bunker near the center of the island (see Figures 7-108 and 7-109). Yvonne was the site for more nuclear events and other test-related activities than any other island in the Atoll, and has therefore suffered the most extensive damage. ground zeros (GZ's) on Yvonne, all but one being on northern Yvonne. There were eight surface Yvonne was also the target for one airdropped bomb, and was affected by another airdrop bomb and by eight barge shots in the lagoon near the island. Yvonne was also subjected to extensive soil movement, excavation and construction related to the numerous buildings and scientific stations on the island. Several areas were also known or suspected to contain buried radioactive materials, and there was a large amount of contaminated scrap on the island and adjacent reef. The GZ's for both of the first two nuclear events on Yvonne, Zebra and Dog, were at the north end of the island, east of the location that was to become the Cactus event crater. Throwout from the Cactus event later covered the contamination from these two events and also covered possible sites of contaminated debris burials for these events. Lacrosse, the next event, was on the reef at the north end of Yvonne on anartificial island. The artificial island was destroyed by the event, leaving a waterfilled crater. There were large arrays of instrumentation associated with the Lacrosse event, and these left behind a large quantity of contaminated and activated rubble on the reef. The fourth event, Erie, was a tower shot on southern Yvonne. This event left heavy contamination on the island, although much of it had decayed or eroded away by the time of cleanup. Also, there were a number of scientific test packages for Erie that were mounted in such a way that the event would cause them to impact on the island. In order to recover these packages, the impact area was extensively plowed, and thousands of cubic meters of soil were removed and sifted. The soil was eventually replaced in the impact area and regraded, and this resulted in a relatively constant distribution of radioactivity with depth to about 15 em below the surface in the Erie area. Some contaminated debris might also have been buried near the GZ during these postshot operations. After the Erie event, the soil in the central part of Yvonne was turned under with bulldozers to reduce the radiation exposure of personnel preparing for the next event, Blackfoot. Blackfoot was a tower shot near the center of Yvonne which heavily contaminated the area near the GZ. A few days later, the Osage device contamination to the island. was airdropped over central Yvonne, but did Cactus, the sixth event on Yvonne, took place at the north end of the island. not add significant The event created a crater and produced large quantities of contaminated ejecta. The highest gamma exposure rates in Atoll soil were found in the Cactus crater lip materiaL The Cactus event crater was selected as the repository for contaminated soil and debris in the 1977-80 radiological cleanup of the Atoll. The primary source of the present plutonium contamination on Yvonne was the final two events, Quince and Fig, especially the former. The Quince event had no nuclear yield, so the high explosives in the device simply scattered the plutonium fuel over the area near the GZ. Because Fig was scheduled for the same GZ, decontamination procedures were implemented immediately. These procedures included removing some soil and contaminated debris, and scraping soil to the side and covering it with uncontaminated soil. There were some inconsistencies in the reports about where the soil was pushed when it was scraped aside. Official reports state that the material was pushed 336