Electrical resistivity tomography (ERT) can be an effective tool to investigate both geologic and hydrogeologic variability in the shallow subsurface. The inverse relationship between conductivity and resistivity allows for ERT to assist in identifying saturated versus unsaturated conditions and to distinguish between various stratigraphy such as sands, clays, and bedrock of varying integrity. Furthermore, ERT testing can help to identify subsurface anomalies that could be considered geo-hazards for exploration activities. This presentation will provide an overview of an ERT testing program implemented at three sites in the western portion of the United States that was used to: 1) Provide a detailed understanding of subsurface geologic stratigraphy (differentiating between sandy soils, bedrock and clay units), 2) Identify the depth of the water table and the transition to saturated conditions, and 3) Delineate and constrain specific aquifer formations. ERT test results were combined with site-specific drilling logs and regional aquifer depth information to establish a more comprehensive understanding of hydrogeologic behavior at the project sites.
