The AGI SuperSting R8/IP unit is a common sight on our project sites around Madison. We deploy a multi-electrode cable, lay it across the glacial outwash plains near the Yahara River, and run a dipole-dipole array to map subsurface resistivity contrasts before any excavator breaks ground. The logic is simple: different materials resist current flow differently. Saturated silty clay from the old Lake Yahara basin reads low resistivity, while dry sand and gravel terrace deposits push readings higher. For deeper targets—like mapping the top of the weathered sandstone bedrock beneath the east side—we switch to a Schlumberger VES spread, expanding electrode spacing step by step to build a layered resistivity model. In a city where the geology shifts from marsh deposits to glacial till within half a mile, this approach gives us a continuous profile that auger borings alone cannot match, and it pairs well with a CPT program when we need to correlate resistivity with cone tip resistance in transitional soils.
In glacial lake plain settings like Madison's isthmus, a 2D resistivity line can delineate organic silt pockets that standard borings miss between grid points.
