Evaluation of uncertainties due to hydrogeological modeling and groundwater flow analysis: Effective continuum model using TOUGH2

Starting with regional geographic, geologic, hydrologic, geophysical, and meteorological data, we develop an effective continuum model to simulate subsurface flow and transport in a 4 km by 6 km by 3 km thick fractured granite rock mass overlain sedimentary layers. Individual fractures are not modeled explicitly. Rather, continuum permeability and porosity distributions are assigned stochastically, based on well-test data and fracture density measurements. Large-scale features such as lithologic layering and major fault zones are assigned deterministically. We employ the TOUGH2 simulator for the flow calculation. The model simulates the steady-state groundwater flow through the site, then streamline analysis is used to calculate travel times for particles leaving specified monitoring points to reach the boundary of the model. Model results for the head distribution compare favorably with head profiles measured in several deep boreholes and the overall groundwater flow is consistent with regional water balance data. Predicted travel times range from 1 to 25 years