An electrical resistivity survey would NOT be used to differentiate which of the following?

• A. Groundwater plumes
• B. Bedrock depth
• C. Coal beds from limestone
• D. Lateral extent of sedimentary units

Answer: (C)

Electrical resistivity surveys rely on contrasts in how easily electricity moves through subsurface materials, which depends on porosity, fluid content, and salinity. They are especially good at identifying conductive groundwater plumes, estimating depth to bedrock where the sediment–rock boundary creates a sharp resistivity change, and mapping lateral changes in sedimentary units that have different porosity or saturation.

Distinguishing coal beds from limestone is problematic because coal and limestone can exhibit similar resistivity values when coal is water- or gas-saturated and the groundwater chemistry varies. This overlap makes it hard to separate these two lithologies using resistivity alone, so this survey isn’t the most reliable tool for differentiating coal beds from limestone. In practice, borehole data or other geophysical methods would be used to confirm lithology.