Spatial Variability in Subsurface Flow Through the Unsaturated Zone in the Vicinity of the Pantex Plant, Southern High Plains, Texas

Many of the previous studies of the High Plains have assumed that recharge to the underlying Ogallala aquifer is uniformly distributed. Use of areally averaged recharge rates greatly underestimates contaminant transport velocities in areas of focused flow. The objective of this study was to evaluate spatial variability in subsurface water movement at a variety of scales that ranged from playa/interplaya scale to desiccation crack/root tubule scale. The study was conducted in the vicinity of the Department of Energy's Pantex Plant, near Amarillo, Texas.

Hydraulic and chemical approaches were used to evaluate subsurface flow in natural playa and interplaya settings. A maximum of 35 boreholes from 7 playa/interplaya settings were sampled. Hydraulic methods included laboratory measurement of water content and water potential. Chemical tracers included meteoric chloride, chlorine-36, and tritium. To evaluate preferential flow in surficial sediments, applied tracers such as bromide and organic dyes were used.