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Applications of Controlled-Source and Natural-Source AMT to Groundwater Exploration

Publisher —
Environmental and Engineering Geophysical Society (EEGS), 2005 Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP) proceedings.

Authors —
Norman R. Carlson*, Zonge Engineering & Research Organization, Tucson, Arizona;
Phillip M. Paski, HydroSystems, Inc., Tempe, Arizona;
Scott A. Urquhart*, Zonge Engineering & Research Organization, Tucson, Arizona.

Paper — [pdf] GRW_SAGEEP05Groundwater

Audio-frequency magnetotellurics (AMT), using either a controlled-source (CSAMT) or natural-source, has become an efficient, cost-effective tool for groundwater exploration. Advancements in field equipment have improved data quality and increased data acquisition speed, and the availability of 2D inversion modeling has significantly improved interpretation. Since depth of investigation is not related to the receiver electric field dipole size, AMT can be used as either a high-resolution tool (using short dipoles) or as a reconnaissance tool (using large dipoles).
This paper presents several field examples of CSAMT investigations for groundwater exploration, including surveys for fractured bedrock targets in which lateral resolution is important, as well as reconnaissance-style basin mapping in which speed and economic efficiency is critical. In one Nevada project, CSAMT was used successfully to map an undeveloped basin and was instrumental in subsequent court hearings to support water-right applications to develop the groundwater resources.