Use of Electrical Resistivity Profiling to Reduce Landfill Siting Risks in the South Central Kentucky Karst

Abstract Electrical Resistivity (ER) can be a key tool for aiding in characterization of karst geohazard risks at proposed landfill sites. This focused study is proximal to the south central Kentucky karst and Mammoth Cave National Park and possesses siliciclastic cap rock upland areas that pose relatively high groundwater-contamination risks due to adjacent ravines floored by carbonates. Complex stratigraphy associated with the Mississippian-Pennsylvanian unconformity and juxtaposition of heterolithic sedimentary rocks in general presents further challenges for demarcating hydrogeological characterization of the base of engineered landfills. A conceptual site model integrates ER surveying and field geology that both satisfactorily characterize the site and risks to groundwater resources without conducting multiple borings. Our work entails two ER profiles that traversed the site, study of outcrops, an excavated pit and trench and briefly compares the focus study area to regional sites with caves. ER data range from several low 10s to about 400 ohm-meter values for mud rock units whereas sandy units possess ER values from approximately 500 to several 10 tens of thousands of ohm meters. The greatest values are indicative of basal Pennsylvanian Caseyville Sandstone and these exceed 32,000 ohm meters. An unexpected challenge specific to this study includes occurrence of well-drained and highly weathered Caseyville at the highest elevations of the site where electrical contact was not possible during ER surveying. The overall ER contrast however, between quartz-rich and clay poor strata (high-resistivity rocks) and clay-rich strata (low-resistivity rocks) provides independent data consistent with the observed stratigraphy exposed in site exposures.