Analysis of Hydraulic Gradients Across the Host Rock at the Proposed Texas Panhandle Nuclear‐Waste Repository Site

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Abstract
Analysis of the direction of ground‐water flow across the host rock at the proposed high‐level nuclear‐waste repository site in Deaf Smith County, Texas, is complicated by vertical and lateral changes in the density of formation fluids in the various hydrogeologic units that overlie and underlie the proposed host rock. Because the concept of hydraulic head is not valid when evaluating vertical hydraulic gradients in a variable‐density flow system, other methods were used to determine the direction and magnitude of vertical hydraulic gradients at the proposed site where the specific gravity of formation fluids varies between 1.00 and 1.28. The direction of ground‐water flow across the proposed host rock, an 80‐foot‐thick salt bed in the Lower San Andres Formation, was determined by calculating vertical hydraulic gradients based on formation pressure and fluid density data, and by analysis of pressure‐depth diagrams. Based on data from the vicinity of the proposed site, both methods indicate the potential for downflow across the host rock. Downflow or predominantly horizontal flow is considered a favorable prewaste emplacement condition because it prolongs the‐travel time to the biosphere of any naturally or accidentally released radionuclides.