29 of the dome, may be near “equilibrium® since it is close to the maximun extension of the near subsurface beachrock (Byron Ristvet, letter to the committee, November 1961). The committee believes that the probability of dome breachment due to storm wave and typhoon activity is quite low.’ However, to facili- tate early detection of typhoon-induced effects it recommends that visual inspection of the dome structure, the surrounding mole, and the beach on the lagoon side be performed at regular intervals (as a mininum, after each major typhoon). Some settling with time in response to loading is conceivable. Purthermore, vegetation such as tree limbs included within the debris Gan be expected to undergo bacteriological reduction, resulting in slight amounts of settlement within the dome. Such settlement, however, would not impair the function of the dome cap in denying human access to the contained material. dome cap in response to wided by the key-wall. slightly in response to cap functions simply as Resistance against movement of the settlement of the contents of the dome is proAlthough the key-wall may spread outward stresses produced by settlement, the concrete a series of cover slabs, not a true dome structure, and can easily bridge over any localized areas of differen- tial settlement or settle without any impairment of the dome'’s per~ formance. 3.7 Bazards Associated with Leaching from the Containment Structure The results of the drilling program deseribed in chapter 4 show that the tremie and the soil-cement operations were not fully successful. Within the tremie region there are zones of oversized debris and unconsolidated tremie material that provide channels for water movement. The rapid tidal response in the boreholes indicates that the water in the structure is closely coupled to the island's groundwater. Therefore, at least part of the radioactivity contained in the structure is available for transport to the groundwater and, subsequently, to the lagoon, and it is important to determine whether this pathway may be a significant one. It is not clear whether Cactus Crater (and its vicinity) is a Greater or lesser source of transuranic movement to the lagoon than it was before the cleanup. Before Cactus Crater was filled it was one of the sources of transuranics being remobilized to the waters of the lagoon. Noshkin estimates that about 0.4 percent of the dissolved Plutonium present in the lagoon originated from the material at the bottom of the crater (V.E. Noshkin, personal communication to R.W. Morse, October 23, 1981). Several conditions, however, were changed by the cleanup operations: the fresh water run-off to the water table was changed by the construction of the dome; the cleanup of soil on the island has reduced movement of transuranics to the groundwater; and the filling of the crater has modified the amount of transuranics being transported from the crater. Tt is possible to demonstrate that leaching from the dome does not Create a significant new hazard by use of simple inventory arguments without having to speculate ebout possible remobilization processes taking place within the structure. It was indicated in section 5.3 that there is about 1.5 Ci of plutonium continuously in solution in the lagoon and that 3.0 Ci are lost to the ocean annually. SOG8 S54 u: The amount of