Review of the 2008 resistivity surveys at the WCS facility, Andrews County, Texas

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2009

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Technos, Inc. completed two resistivity surveys on behalf of Waste Control Specialists, LLC (WCS) at the WCS facility in Andrews County, Texas. These surveys, conducted between January 24-27, 2008, and August 29-September 2, 2008, are summarized in three reports (Technos 2008a, 2008b, and 2008c). Results of the January survey, including processing and analysis of resistivity lines A and B extending northeast from the northern boundary of the proposed Federal Waste Disposal Facility, are reported in Technos 2008a. Discussion of those results led to additional resistivity surveying along lines C and D, which extend across and northward from the Byproduct Disposal Site as described in Technos 2008b. The general lack of agreement between processed resistivity data and known depths to a significant conductive layer (the redbeds) identified in boreholes and in geophysical logs led to additional processing and analysis of the resistivity data, which is summarized in a supplemental report (Technos 2008c). Technos subsequently provided resistivity data files from both surveys to allow a preliminary independent assessment of the resistivity data.

Troubling aspects from the report on the January 2008 survey included: (a) the poor agreement between the resistivity-depth sections and the known depth to a relatively conductive layer (the resistivity data significantly overestimated the depth to the redbeds), (b) the poor agreement between borehole conductivity data and resistivity values in the inverted depth sections, and (c) the conclusion that surface resistivity data would not be useful in examining water saturation trends in the shallow subsurface at the site.

Many of the same issues remained in the second report following the August-September acquisition and processing. The supplemental processing described in Technos 2008c was intended to address these issues by reprocessing the resistivity data and examining trends in unprocessed data at different electrode spacings to identify a possible relationship between water saturation and apparent resistivity but only partly satisfied that objective. We have briefly examined the raw resistivity data provided by Technos to further investigate issues of conversion of raw resistivity data to true resistivity-depth profiles and possible correlations between field data and water saturation along lines A, B, C, and D.

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