In May 2008, EM surveys were conducted around three saline lakes near the Crescent Lake National Wildlife Refuge in the Sand Hills of western Nebraska. Over 25 km of data were collected per day by mounting the GPS-enabled EM instrument to a fiberglass cart and towing with an all-terrain vehicle (ATV). Data were collected at 15 frequencies from 3-63 kHz. Field-plotting of the geo-referenced data revealed trends in EM conductivity distribution around the lakes. The lowest conductivities (<10 mS/m) were found along the northern and western shores, with the highest conductivities (>100-500 mS/m) focused on the eastern and southern shores, consistent with regional and local ground-water flow directions. In addition, the EM data delineated numerous specific targets for follow-up ERT testing, and comparison of high- and low-frequency EM data enabled prediction of ground water salinity trends with depth. This study showed that use of towed EM conductivity methods is an effective way to perform rapid geophysical reconnaissance of saline lake environments.
See more of: Topical Sessions