Incorporating interpretation uncertainties from deterministic 3D hydrostratigraphic models in groundwater models

Abstract. Many 3D hydrostratigraphic models of the subsurface are interpreted as deterministic models, where an experienced modeler combines relevant geophysical and geological information with background geological knowledge. Depending on the quality of the information from the input data, the interpretation phase will typically be accompanied by an estimated qualitative interpretation uncertainty. Given the qualitative and subjective nature of uncertainty, it is difficult to propagate the uncertainty to groundwater models. In this study, a stochastic simulation-based methodology to characterize interpretation uncertainty within a manual interpretation-based layer model is applied in a groundwater modeling setting. Three levels of interpretation uncertainty scenarios are generated and three locations in the models representing different geological structures are analyzed. The impact of interpretation uncertainty on predictions of capture zone area and median travel time is compared to the impact of uncertainty on parameters in the groundwater model. The main result is that in areas with thick and large aquifers and low geological uncertainty, the impact of interpretation uncertainty is negligible compared to the hydrogeological parameterization, while it may introduce a significant contribution in areas with thinner and smaller aquifers with high geologic uncertainty. The influence of the interpretation uncertainties is thus dependent on the geological setting as well as the confidence of the interpreter. In areas with thick aquifers, this study confirms existing evidence that if the conceptual model is well-defined, interpretation uncertainties within the conceptual model have limited impact on groundwater model predictions.