We examine the identification of large-scale spatial trends in hydraulic conductivity and the influence of these trends on contaminant transport. Using three different trend identification methods, polynomial regression and Kalman filtering, which fit smooth functions, and hydrofacies delineation, which constructs a geologic model, we try to identify the hydraulic conductivity patterns controlling solute transport in a heavily sampled heterogeneous aquifer on Columbus Air Force Base, Mississippi. Even with >2400 hydraulic conductivity measurements, unambiguous determination of large-scale trends is not possible. None of the estimated hydraulic conductivity trends gives transport simulations that reproduce the observed non-Gaussian transport behavior. Hydrofacies delineation and Kalman filtering give the best results. While the influence of the identified large-scale trends on advective transport is significant, accurate prediction of contaminant transport requires knowledge of small-scale (<10 m) hydraulic conductivity structures. ¿ 1998 American Geophysical Union