Geophysical Studies For The Exploration Of Ground Water In The Basin And Range Of Northern Nevada

In support of a proposed large coal-fired generating station in<br>northern Nevada, large amounts of ground water within a few hundred feet of<br>the surface needed to be identified. Surface geophysical test surveys consisting<br>of central-loop time domain electromagnetic (TDEM) soundings and<br>dipole-dipole resistivity profiling, were conducted in selected areas where<br>drilling control was available. Based on these results, the TDEM method<br>was chosen for a basin-wide reconnaissance to identify strata of coarsegrained<br>sediments for further exploration with test wells.<br>The survey was conducted in a typical basin of the Basin and Range<br>Province of northern Nevada. Potential water producing horizons in the<br>Basin consist of a variety of unconsolidated sediments, including volcanoclastics,<br>ash falls, lake beds, and colluvium. The more productive<br>"water bearing" formations are the coarser-grained, relatively "well sorted"<br>portions of these units which usually occur in paleo-alluvial drainages.<br>These are identified in the TDEM sounding inversions as higher<br>resistivity units compared to adjacent clay-rich units.<br>Geoelectric soundings using TDEM proved to be a rapid and effective<br>method of measuring subsurface resistivities to the depths required for<br>this investigation.