(4) Except for Bikini and Eneu all the other islands comprising Bikini Atoll show evidence of some degree of shoreline erosion and wave overwash. Because of their low elevation, exposure to wave action and small size all would appear to be too hazardous for permanent habitation. All of the southern islands are situated very close to the outer edge of the ocean reef flat (in most cases 100-200 m), increasing their vulnerability to storm waves. Even the northern islands show recent evidence of shoreline erosion from the southern lagoon side, possibly the result of large waves entering the lagoon via the wide southeastern passage. The reef platform that comprises the uppermost visible perimeter of the Bikini Atoll forms a shallow terrace to depths of 20 m'to widths of 2-3, km. Seaward of the shallow terrace, however, the ocean bottom generally drops precipitously, and at a distance of 5 km from Bikini. Island ocean depths are approximately 2000 m and within 8 km are as great as 3000 m (see Figure 3). The Bikini lagoon, which covers some 632 km2, has an average depth of 45 m and a maximum depth of 58m. The lagoon floor generally is quite flat and consists mainly of loose sandy and silty carbonate sediments except for the occurrence of numerous coral pinnacles and patch reefs, some of which may exceed a km in diameter and stand several tens of meters high; very few, however, are located near Bikini and Eneu Islands. The sediments that make up the lagoon bottom essentially are of 5 types: fine debris, corals, Foraminifera, Halimeda, and mollusk shells (Emery, Tracey, and Ladd, 1954). Generally the shallowest parts of the lagoon bottom near the reef flats are covered with fine debris with a particle size averaging less than about 0.5 mm is, diameter, which consists primarily of skeletons of reef organisms. Throughout the rest of the lagoon, the calcareous remains of the alga Halimeda up to about a centimeter across are the most abundant constituent of the bottom sediments, except in a few deeper areas where Foraminifera are abundant. Island. Figure 5 shows the distribution of bottom material near Bikini Of special interest for this Committee is the suitability of lagoon bottom sediments for use as topping material should existing soil be removed from one or more islands. In this regard several characteristics of the bottom material are of importance: + their ease of dredging, (2) their radioactivity, and (3) their fertility (with respect to plant growth). As can be seen from Figure 4, large quantities of loose easily dredgeable sediments are available at shallow depths near Bikini and Eneu Islands. Studies on the radionuclides of the top layer of sediment (0-12 cm) have shown low levels of radioactivity in the entire area within 15 km of Bikini and Eneu Islands (Figure 5); however, the depth profile of specific activity is not well known for the lagoon sediment. Recent work by McMurtry, et al, (in press) in Enewetak Atoll shows no consistent decrease in activity within the upper 200 cm of lagoon sediment, and in fact, in some cases the radioactivity increases ~ dramatically at depth. They attribute these results primarily to bioturbation from benthic invertebrates and possibly to constant natural sedimentation since the testing era, resulting in burial of the more radioactive layer. The results from bottom samples collected in November, 1983 in Bikini Lagoon — should provide additional information when analyses are completed by Lawrence Livermore Laboratory. I0000b& A-3