A Comparison of Six Transport Models of the MADE-1 Experiment Implemented with Different Types of Hydraulic Data

Six conceptually different transport models are applied to the MADE-1 field tracer experiement as a first major attempt for model comparison. The objective was to show that complex mass distributions in heterogeneous aquifers can be predicted without calibration of transport parameters - solely making use of structural and flow data. The models differ in their conceptualization of the heterogeneous aquifer structure, computational complexity, and use of conductivity data obtained from various observation methods (Direct Push Injection Logging - DPIL, Grain Size Analysis, Pumping Tests and Flowmeter). They agree in the underlying physical transport processes, none of them considering mass transfer. Predictive capability is assessed by comparing results to observed longitudinal mass distributions of the MADE-1 experiment. We deal with data uncertainty indicated by decreasing rates of recovered mass by focusing the comparison on measures, such as peak location, position and shape of bulk mass and leading tail, and we do not normalize observation data. Comparison of models reveals that the predictions of the solute plume agree reasonably well with observations if the models are underlined by a few parameters of close values: mean velocity, a parameter reflecting log-conductivity variability and a horizontal length scale related to conductivity spatial correlation. The robustness of the results implies that conservative transport models with appropriate conductivity upscaling strategies of various observation data provide reasonable predictions of plumes longitudinal mass distribution as long as key features are taken into account.