Ground-water flow modeling of the Culebra dolomite

This hydrogeologic modeling study has been performed as part of the regional hydrologic characterization of the Waste Isolation Pilot Plant (WIPP) site in southeastern New Mexico. The study has produced an estimation of the transmissivity and Darcy-velocity distributions in the Culebra Dolomite Member of the Permian Rustler Formation at the WIPP site. The results of this study are intended to support Sandia National Laboratories performance-assessment calculations. The three-dimensional finite-difference code SWIFT II was employed for the numerical modeling, using a variable-fluid-density and single-porosity formulation. The spatial scale of the model, 21.3 km by 30.6 km, was chosen to allow simulation of regional-scale pumping tests conducted at the H-3 and H-11 hydropads and the WIPP-13 borehole, which are located south, southeast, and northwest, respectively, of the center of the WIPP site. The modeled area includes and extends beyond the controlled area defined by the WIPP-site boundaries. The work performed in this study consisted of modeling the hydrogeology of the Culebra in two stages: steady-state modeling to develop the best estimate of the undisturbed head distribution (i.e., of the hydraulic conditions before excavation of the WIPP shafts, which began in 1981) and superimposed transient modeling of local hydrologic response to excavation ofmore » the four WIPP shafts at the center of the WIPP site, as well as to various well tests. The transient modeling used the calculated steady-state freshwater heads as initial conditions. 144 refs., 98 figs., 23 tabs.« less