12The lack of hydrogeological data and knowledge often results in different propositions (or 13 alternatives) to represent uncertain model components and creates many candidate groundwater 14 models using the same data. Uncertainty of groundwater head prediction may become 15 unnecessarily high. This study introduces an experimental design to identify propositions in each 16 uncertain model component and decrease the prediction uncertainty by reducing conceptual 17 model uncertainty. A discrimination criterion is developed based on posterior model probability 18 that directly uses data to evaluate model importance. Bayesian model averaging (BMA) is used 19 to predict future observation data. The experimental design aims to find the optimal number and 20 location of future observations and the number of sampling rounds such that the desired 21 discrimination criterion is met. Hierarchical Bayesian model averaging (HBMA) is adopted to 22 assess if highly probable propositions can be identified and the conceptual model uncertainty can 23 be reduced by the experimental design. The experimental design is implemented to a 24 groundwater study in the Baton Rouge area, Louisiana. We design a new groundwater head 25 observation network based on existing USGS observation wells. The sources of uncertainty that 26 create multiple groundwater models are geological architecture, boundary condition, and fault 27 permeability architecture. All possible design solutions are enumerated using a multi-core 28 supercomputer. Several design solutions are found to achieve an 80%-identifiable groundwater 29 model in five years by using six or more existing USGS wells. The HBMA result shows that 30 each highly probable proposition can be identified for each uncertain model component once the 31 discrimination criterion is achieved. The variances of groundwater head predictions are 32 significantly decreased by reducing posterior model probabilities of unimportant propositions. 33 34 Keywords: Bayesian model averaging, experimental design, groundwater, model discrimination, 35 observation network design, uncertainty. 36 37The lack of hydrogeological data and knowledge often results in different propositions 60 (or alternatives) to represent uncertain model components and creates many candidate 61 groundwater models using the same data. For example, geological architecture can be one 62 uncertain model component in groundwater modeling. Many hydrostratigraphy modeling 63 techniques may be proposed to construct different geological architectures (propositions) 64 potentially leading to an overwhelming number of models with non-dominant posterior model 65 probabilities. Conducting prediction and uncertainty analysis using a great deal of 66 computationally intensive groundwater models can become intractable. By incorporating many 67 conceptual models, prediction results using BMA can become useless when the prediction 68 uncertainty is very high. This concern highlights the importance of conducting an experimental 69 design to discriminate g...