Consideration of Impacts of Soil Disposal on Northern Runit (Yvonne) Island and the Marine Environment ]. Terrestrial Disposal The present proposed method for handling the terrestrial contaminated soils involves movement to Northern Runit Island and eventually fabricating a mix with cement and capping the resulting soil-cement matrix with 18" of high strength concrete. As long as the concrete cap is intact, remobilization of Pu in the above ground soil to the groundwater would be minimal and the terrestrial plutonium inventory (except that in contact with the groundwater) under the cap would be unavailable to the marine environment. However, the freshwater runoff from the concrete cap might very well cause more rapid remobilization of residual radionuclides in the soil around the perimeter of the cap and could conceivably cause rapid soil erosion around the cap perimeter. This pathway would increase the radionuclide transport rate to the island groundwater around the cap. The ground area affected by runoff is unknown until the cap dimensions are established. The freshwater will have an additional impacts on the near shore marine environment. water salinity. Coral, for example, is very sensitive to Salinity changes which could occur during one heavy rain storm from runoff would be enough to affect growth. It is recommended that some thought be given to designing a water catchment system around the bottom of the cap to reduce tre impact of freshwater runoff. Such a cistern would have added advantages in that a valuable resource, mainly quantities of freshwater, would be available to future inhabitants. The present estimated inventory of 7?%t?*°Pu on Runit Island is 10 curies. | Based upon 1972 survey data? it is possible, although not