Evaluating geologically contrained models with pumping tests in a heterogeneous alluvial aquifer, Helipad Site at Lawrence Livermore National Laboratory, California

Pumping test results and numerical groundwater simulation at the Helipad Site, Lawrence Livermore National Laboratory (LLNL), are used to evaluate four geologically-constrained conceptual models. These include a homogenous-layered model, a homogeneous-layered model, a transition probability geostatistical model, and a stratigraphic transition probability geostatistical model. Each of these models incorporates different aspects of physical heterogeneity observed at this site. At the Helipad Site at LLNL, relatively mature paleosols within the alluvial deposits mark unconformities that separate this alluvial aquifer into a series of stratigraphic zones. This provided the stratigraphic framework in which conceptual models were developed. The results of this study show that multiple realizations for the distributions of hydrofacies within stratigraphic and paleosol units (modeled using transition probability geostatistics) better match pumping test results then conceptual modeling approaches that did not incorporate these finer scale heterogeneities. Based on multiple realizations of hydrofacies distributions, characteristics for the distributions and dimensions of gravel and sand channel were identified that could be later used to filter potential poorly performing realization.