Conclusions from WG-4: the analyses of the alligator rivers natural analogue

The Alligator Rivers study is based on work conducted at the Koongarra uranium deposit about 200 km east of Darwin, Australia. The Alligator Rivers Analogue Project (ARAP) was set up in 1987 and was later included as a test case in both phase 1 and 2 of the INTRAVAL international project about flow and transport processes in sedimentary formations. The objective was to develop a consistent picture of the processes that have controlled the transport in the weathered zone of the Koongarra ore deposit and the time scale over which they have operated. The work included in phase 1 was mainly concentrated to hydrogeological and geochemical modelling which produced results that were used in phase 2 in simulations of the uranium migration. The model concepts were based on rather simple performance assessment models accounting for advection, dispersion and linear sorption in one or two dimensions. One 1-D model was extended to include alpha-recoil and transfer between solid phases. The vertical movement of the weathering front was included in the 2-D model. (J.S.). 3 refs., 9 figs