YUCCA MOUNTAIN SITE-SCALE FLOW MODEL: SENSITIVITY TO HYDROSTRATIGRAPHY MODEL, BOUNDARY FLUX AND HEAD MEASUREMENTS

Modeling work to understand saturated zone groundwater flow at and around Yucca Mountain, NV was done by Los Alamos Natl. Lab. for the Yucca Mountain Project as part of the 2002 Site Recommendation. The model will also be used to provide flow fields in support of the Total Systems Performance Assessment (TSPA) for the upcoming license application. This ongoing study constantly incorporates new data and concepts to insure that models are consistent with the most recent available data.

After the time a 'base-case' site-scale saturated zone flow model was developed, in 2003, additional data and analyses include water-level data, a reinterpreted hydrogeologic framework model, revised recharge distribution, modified boundary fluxes, permeability data and 15 new Nye County well head measurements. To evaluate the impact of this additional data on the site-scale flow model and to validate the base-case site-scale saturated zone flow model, five alternate models have been formulated and calibrated which utilize the new data. Evaluation of the alternate model and comparison to the base-case model is through comparison of the hydrogeology, head calibration, boundary flux targets, model construction and formulation, flow-field and flow-paths.

We conclude that the new data has minimal impact on results. In general the range of differences in flow model results is within the overall uncertainty of the parameters that are varied. The five alternate flow model calculations also provide insight into the sensitivity of the flow model results to changes in the input parameters.