During 2002 the Bureau continued hydrological monitoring at the U.S. Department of Energy's (DOE) Pantex Plant near Amarillo, Texas. The plant lies above part of the Ogallala aquifer. We also provided ongoing review of groundwater-quality reports and participated in discussions on how to improve the groundwater-monitoring program at the Pantex Plant. Since 1995 the Bureau has participated with other State agencies in supporting the State Energy Conservation Office in environmental oversight of the Pantex Plant. The monitoring program is designed to evaluate temporal variability in rates of infiltration and evapotranspiration in the top 1 to 2 m of the subsurface. These data are used to determine the potential for upward water movement below this soil zone in several interplaya settings for use in an environmental review and design of an engineered cover for the landfill at the Pantex site. We did detailed numerical simulations to evaluate liquid and vapor fluxes through the unsaturated zone at the Pantex Plant and in other semiarid sites, including Beatty, Nevada, and Sierra Blanca and Fort Hancock in West Texas. Results from the simulations indicate that water has been moving upward through the unsaturated zone in interdrainage settings for long time periods (1,000 to 16,000 yr).