The Hydrogeology Department has extensive expertise (and decades of experience) in exploration of the vadose zone, including playing a leadership role in the vadose-zone field investigations and modeling associated with the Yucca Mountain Project. The Department also has a long and rich research history in the area of fracture hydrology, focusing on theoretical and experimental studies of flow and transport in fractured rock. Hydrogeology Department researchers have made significant contributions to identifying the physical mechanisms, and developing modeling approaches and characterization/ monitoring techniques, for flow and transport in fractures in both saturated and unsaturated systems. A number of important concepts in this area have been initialized by Hydrogeology Department researchers and their collaborators, including the impact of fracture roughness on the validity of cubic law, channelized flow in saturated fractured rock, film flow in unsaturated fractures, chaotic behavior of multiphase flow, and the scale dependency of the matrix diffusion coefficient. In addition, advanced field technologies and interpretation techniques have been developed for characterizing fractured porous media. The characterization/monitoring techniques span the range from manual measurements made in tunnels and drift, to remote in situ measurements in boreholes, to noninvasive geophysical techniques.