62 crater depression and contained smaller amounts of fine sediments (see Sec. 5.2). In the samples collected from the Bravo Crater area, each individual station concentration jis shown, due to the large and systematic variation in the concentrations of some (but not all) radionuclides which occurred at the five collection sites across the diameter of the crater. 51-1) Plutonium-239+240 The areal] distribution of 239+2405 in surface sediments is shown in Figure 11. The most striking characteristic of the distribution is the high concentration in the northwest quadrant of the lagoon. The concentra- tions measured in this portion of the lagoon are more than two times greater than the concentrations measured in any crater station surface sediment. The concentration around this area decreases rapidly with distance away from stations B-2 and B-20, particularly to the southwest. Because only a few sampling stations were established around this region of high 239+240 Pu concen- trations, especially to the north and east of Stations B-2 and 8-20, it is not possible to delineate the shape or structure of the concentration gradients existing in this area with certainty. The data show that the major distribu- tion of 23942405, across the lagoon is centered in the northwest quadrant of the lagoon and decreases roughly exponentially along a line which is parallel to the northern reef. The lowest concentrations measured fell between 3 and 5 pCi/g and were observed in several collections from the eastern and southern regions of the lagoon. These low concentrations are 2.5 to 4.5 % of the highest concentration measured in the northwest quadrant of the lagoon. The 23942405 concentrations measured in sediments from three sampling Stations (B-18, B-30, and Zuni Crater) are significantly higher than the concentrations measured at nearby stations. These high concentrations probably reflect the localized, and apparently less widespread, areal distributions of