DEVELOPING THE COMPUTATIONAL WORKFLOWS REQUIRED TO ADVANCE THE USE OF AIRBORNE ELECTROMAGNETIC DATA IN CHARACTERIZING THE GROUNDWATER SYSTEMS OF CALIFORNIA

Over the past decade, a number of studies involving the acquisition of airborne electromagnetic (AEM) data have demonstrated the potential for using this form of data in characterizing the groundwater systems of California. We have developed a number of computational workflows for the analysis and interpretation of AEM data, integrated with drillers’ logs, with each workflow tailored to address a specific need in local decision-making. For the development of the hydrogeologic conceptual model, required as input to a groundwater model, we have developed a targeted inversion approach that provides a high level of accuracy in imaging the large-scale structure of a groundwater system. As an example, we have imaged the Corcoran Clay, the major confining unit in the southern Central Valley, improving previous attempts to do so with AEM data and refining what has been determined with drillers’ logs. This targeted inversion approach also allows us to accurately image the bedrock surface, thus providing critical information about a boundary typically under-sampled in the drillers’ logs. At the smaller scale, there is a need to map out the spatial variability in sediment type in a way that benefits from the vertical resolution achieved in drillers’ logs and from the lateral continuity and depth-of-imaging provided by the AEM data. For this problem we developed a workflow that adopts multi-point statistics (MPS) as the numerical framework for integrating the AEM data with drillers’ logs and with existing geologic knowledge. This allows us to create many models imaging both large-scale and smaller-scale variation in sediment type. Our final example addresses the growing need for information to support local decision-making regarding the development of recharge operations. With the large volume of AEM data now available from the Department of Water Resources state-wide project, we have developed a workflow, available as a web-based application fastpath, that can be used to assess the suitability of areas as sites for surface-spreading recharge. A set of results are now available for the Central Valley, presented as plan-view maps displaying suitability for recharge. These maps are valid at the scale at which the AEM data were acquired, so are best used to select areas where further ground-based studies can be conducted.