Understanding how contaminants behave in the subsurface requires both strong scientific foundations and practical tools. In a study by Todd Halihan and colleagues, hydrogeology, geophysics, and laboratory experimentation were combined to better understand how electrical resistivity imaging (ERI) detects non-aqueous phase liquids (NAPLs) in groundwater systems. Their work provides important insight into the mechanisms behind the resistive anomalies often observed in ERI surveys at contaminated sites.
The study investigates a key question: why do NAPL plumes appear as strong resistive signals in ERI data? The authors propose an “electrical barrier” mechanism, showing that NAPL does not simply change bulk conductivity through volume alone. Instead, thin NAPL films can form within pore spaces and act as barriers that disrupt electrical current pathways through saturated soils.
To test this concept, the research team combined modeling, controlled sand tank experiments, and ERI measurements. Optical imaging tracked NAPL distribution within the tank while resistivity data measured the electrical response. The results showed that even relatively small NAPL accumulations (3.3 cm or greater) can generate significant resistivity contrasts when they interrupt conductive pathways in the pore network.
At Aestus, this research directly informs how we apply ERI in the field. By understanding the electrical barrier behavior of NAPL, our GeoTrax Survey™ approach focuses on identifying resistivity patterns that indicate disrupted current flow rather than simply searching for bulk conductivity changes. This allows us to better locate residual source zones, refine conceptual site models, and guide targeted drilling or remediation strategies.
Bridging research and practice is critical for solving complex subsurface problems—and advances like this help turn geophysical signals into actionable environmental insight.
