Examining shallow stratigraphic, lithologic, and water-saturation trends at the WCS facility, Andrews County, Texas using electromagnetic induction

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At least two important issues related to the long-term waste disposal site proposed and operated by Waste Control Specialists, Inc. (WCS) in Andrews County, Texas (fig. 1) are related to shallow hydrostratigraphy. These are:

(a) Depth to the clay-rich Triassic Dockum Group that hosts the waste repositories. (b) Subsurface distribution of water within the younger strata (Ogallala-Antlers-Gatuna units, or OAG) above the Dockum Group.

Since the early 1990s, more than 400 borings and wells have been drilled by WCS, aiding in understanding the three-dimensional geologic and hydrologic environment at the WCS site. Nevertheless, uncertainty remains in the understanding of lithologic and hydrologic parameter distribution at and near the repository. Geophysical surveys that measure the electrical conductivity of the subsurface can be applied to help illuminate shallow hydrogeologic issues. At the WCS site, the generally higher clay content characteristic of the Triassic sediments has been shown through borehole geophysical measurements (Technos, 2008a, b) to cause a significant increase in electrical conductivity. Similarly, water saturation within the Ogallala-Antlers-Gatuna (OAG) strata is also associated with an increase in conductivity over lithologically similar strata that are dry (Technos, 2008a, b). Consequently, surface or subsurface geophysical surveys have the potential to augment site-specific borehole data to better define the subsurface distribution of lithologic materials and water.


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