Use of transient electromagnetics to define local hydrogeology in an arid alluvial environment

To characterize a local groundwater system in an arid alluvial environment, a transient electromagnetic (TEM) survey was performed with a dense station spacing along intersecting profiles. Structural features of significance to groundwater development were clearly evident in the color modulated apparent resistivity versus time pseudosections that were used to display the apparent resistivity data. Modeling results in conjunction with pseudosections were used to determine exploratory drill sites. Comparing the modeled results with electric logs from test holes demonstrated that 1-D modeling is not suitable for areas where rapid lateral change occurs. These areas are easily identified in the apparent resistivity versus time pseudosections. Sites not located in fault zones with a resistivity greater than a few tens of ohm‐m were considered to be preferred locations for production wells. Hydraulic testing confirmed this interpretation philosophy. The survey demonstrates the utility of closely spaced TEM soundings to characterize local hydrogeology and to define areas suitable for groundwater development.