Megascopic controls on radionuclide transport in groundwater flow systems

In this paper we investigate how the geologic structure of a basin influences the reliability with which predictions of radionuclide transport within a depository horizon can be made. Results from a series of stochastic simulations show that, in some cases, transport predictions are sensitive to perturbations in the hydraulic properties of surrounding layers, indicating megascopic effects on a basin-wide scale exert a significant control on transport at the macroscopic scale. Other cases are identified where transport is not sensitive to perturbations in the hydraulic properties of surrounding layers. A key factor in this response is the distribution of the hydraulic gradient in the basin