CHALLENGING MODELS FOR FLOW IN UNSATURATED, FRACTURED ROCK THROUGH EXPLORATION OF SMALL-SCALE PROCESSES

Fluid flow in unsaturated, fractured rock is studied with respect to a pplied environmental problems ranging from remediation of existing con taminated sites to evaluation of potential sites for isolation of haza rdous or radioactive wastes. Spatial scales for such problems vary fro m meters to kilometers with temporal scales from months to tens of tho usands of years. Because such scales often preclude direct physical ex ploration of system response and detailed site characterization, we ar e regularly forced to use our understanding (or misunderstanding) of t he underlying physical processes to predict large scale behavior. It i s essential that conceptual models used as the basis for prediction be firmly grounded in physical reality. In this paper, we provide exampl es of how recent advances in understanding of small-scale processes wi thin discrete fractures may influence the behavior of fluid flow in fr acture networks and ensembles of matrix blocks sufficiently to impact the formulation of intermediate-scale effective media properties. We a lso explore, by means of a thought experiment, how these same small-sc ale processes could couple to produce a large-scale system response in consistent with current conceptual models of now through unsaturated, fractured rock.