The Loupe TEM is a transient electromagnetic profiling system for efficient mapping of near-surface ground conductivity. The system is operated by a two-person crew who carry the transmitter coil and 3-component receiver coils on backpacks. Benefits of the system include the high productivity and the ability to survey in various types of terrain and through dense vegetation. In mid-2020, we utilised the Loupe TEM system in the Pilbara region of Western Australia to investigate potential fluid pathways and contamination around an environmental pond. A total of 23.5 km line kilometres of data was acquired on a dense grid with 20 m line spacing. We used a 75 Hz base frequency and stacked 300 transients to improve the signal-to-noise ratio. Data were gridded to highlight spatial features and modelled to create conductivity depth images. Supporting information included a frequency-domain EM survey using Geonics EM-34 equipment, passive seismic data obtained using the Sara GeoBox, and information from groundwater monitoring bores. The results identified various laterally coherent zones with elevated electrical conductivities, some of which related to or appeared to originate from the environmental pond. Features of interest included a shallow clay layer, a likely bedrock shear zone, and possible contamination. The Loupe TEM data correlated well with EM-34 bulk conductivity values, while passive seismic data provided useful supplementary information on bedrock depth. Groundwater sampling data did not always correlate with EM survey results, but without conclusive evidence as to the cause of the discrepancy.

Open-Access Online Publication: March 01, 2023