A COMPARISON OF THE EFFECTIVENESS OF CAPACITIVELY-COUPLED RESISTIVITY VS. DIRECT-CURRENT RESISTIVITY METHODS ON GYPSUM EVAPORITE KARST ALONG FM 2185, CULBERSON COUNTY, TEXAS

Extensive evaporite karst development within the Delaware Basin poses a significant geohazard threat to infrastructure. The dissolution of the evaporite strata of the Permian Castile Formation have led to manifestations of numerous karst geohazard phenomena including sinkholes, subsidence features, and caves. The study area is located within the Gypsum Plain of the Delaware Basin in Culberson County, Texas and includes outcrops of Castile strata that host gypsum karst geohazards.

A 48-kilometer segment of FM 2185 was investigated using a dipole-dipole array configuration with Capacitively-Coupled Resistivity (CCR) and Direct-Current Resistivity (DCR) methods to characterize and delineate karst features that do not manifest at the surface, but pose potential geohazard concerns. Two areas of interest were selected based on their relatively close proximity of surficial karst features. CCR data was acquired using the Geometrics OhmMapper G-858 resistivity system, which is composed of five receivers connected by 2.5-meter coaxial cables and a transmitter offset of 2.5 meters. In combination with the medium analyzed, this geometric configuration enabled resistivity soundings up to 5 meters deep. Two-dimensional DCR data was collected with a SuperSting (R8/IP) multi-electrode earth resistivity meter using 112 electrodes with 2-meter spacing, and enabled a depth of investigation of up to 25 meters in depth. Data was processed using AGI’s (Advanced Geometrics Inc.) EarthImager 2D software and used to delineate karst-related cavities and subsidence features in the shallow subsurface.