Parameterization and upscaling in modeling flow and transport in the unsaturated zone of Yucca Mountain

Parameterization and upscaling for unsaturated rocks are discussed with application to Yucca Mountain in Nevada, the potential site for a geological repository of high-level nuclear waste. A complex three-dimensional model of the unsaturated zone at Yucca mountain (UZ model) has been developed (Bodvarsson et al., 1997) utilizing all of the available data from the site, including those from numerous surface boreholes and underground tunnels. As the typical grid spacing used in the UZ model is on the order of tens of meters to more than 100 m, the parameterization for the model based on much smaller-scale in situ tests and core measurements must be carefully conducted. A methodology for doing this has been developed and used in the UZ model; this methodology is applicable to most other fractured unsaturated sites. The primary upscaling process used in the UZ model is a direct inversion of the observed data, including saturation, moisture tension, pneumatic, perched water, temperature, and geochemical data. The process starts with one-dimensional inversions and then proceeds to two- and three-dimensional inversions.