Airborne, surface, and borehole geophysical surveys were conducted as a major component of a groundwater resource exploration study of arid basins at Fort Irwin National Training Center (NTC) in the Mojave Desert in eastern California. To plan for the long-term water availability at the NTC, water resources are being evaluated in undeveloped groundwater basins underlying the NTC. Most of the undeveloped basins have little to no lithologic or historical hydrologic data, a common scenario for remote, mountainous, and arid regions. To supplement the sparse hydrogeologic observations, two basin- to regional-scale airborne electromagnetic (AEM) and aeromagnetic surveys were conducted over the NTC using different survey designs, providing varying degrees of data density between basins. AEM surveys were compared to available data in each basin and included a combination of ground-based transient electromagnetic surveys, borehole geophysical and lithologic data, geologic cross sections, and previously published estimates of basin-fill thickness derived from gravity data. These data have been used to define subsurface geologic structure, locate faults, and refine the hydrostratigraphic framework of individual basins. A 3D geohydrologic framework model is under development using AEM-derived parameter zones that are constrained by hydrostratigraphic interpretations of borehole hydrologic and lithologic data. A groundwater-flow model is being developed to test different hydraulic properties estimated for the AEM-derived zones to provide a loosely constrained steady-state model. Although the steady-state models are based on sparse data, they can provide general constraints, including available water supply and effects of groundwater withdrawal, which can be used for more informed management decisions.
Maps show AEM flightlines and inverted AEM data at two depths for Leach Basin, California.