f GROUNDWATER EXPLORATION EXAMPLES USING CSAMT AND NSAMT

Although the presence or absence of water in the subsurface obviously should have an effect on the electrical properties of the ground, in the exploration process, particularly in relatively unexplored areas, it is not always immediately clear whether groundwater is a low resistivity target relative to background, or a high resistivity target. In this paper, we discuss one case history in which groundwater production was successful after drilling a high resistivity target, whereas in a nearby project, groundwater production correlated with a low resistivity zone. Correlating the surface geophysical methods (in this case, controlled source and natural source audio-frequency magnetotellurics, or CSAMT and NSAMT) with known and suspected geological and hydrological background information was critical to understanding the production. In both cases, future wells can now be properly planned based on the geophysics.