Several states are currently seeking much-needed new low-level radioactive disposal sites in accordance with the Low-Level Radioactive Waste Policy Act of 1980 Any new commercial or state site must comply with the technical requirements of 10 CFR 61 or comparable state regulations, which include a requirement that a site be capable of being modeled and that its performance be assured for 500 years. For most sites, the hydrogeological and radionuclide transport characteristics of the unsaturated zone are major factors in assessing site performance and therefore must be properly modeled. Current unsaturated zone models cannot accommodate many processes or characteristics that may be important, such as hysteresls, highly variable spatial/temporal conditions, macropores and fractures, non-linear sorptlon, and multi-phase fluid flow The proposed, research project is aimed at developing the key model enhancements needed to enable modeling requirements â«t potential sites to be satisfied phase- I w111 involve development of the numerical approaches to and algorithms for each of the processes and a detailed outline of the overall integrated model Phase- II will involve coding, testing, and model w-verificatio
