Geophysical Methods for Karst Feature Identification at Underground Storage Tank Facilities in Kentucky
Monday, October 2, 2017: 3:15 p.m.
Karst hydrogeology and geomorphology create unique challenges for effectively characterizing contaminant nature and extent at Kentucky Underground Storage Tank (KY UST) sites. Traditional characterization of KY UST releases in karst terrain involved the initial collection of soil samples (saturated and unsaturated) and groundwater samples from the water-table aquifer. For karst sites with contamination extending to the top of carbonate bedrock, monitoring wells were historically installed into rock without first considering the features of the underlying karst geomorphology and the complex flow dynamics of the karst hydrogeology. Wells installed in this manner can provide inadequate information regarding the following critical bedrock elements: i) Transition zone (epikarst) between unconsolidated material and competent carbonate bedrock; ii) Characteristics of the fractured competent carbonate bedrock below the epikarst; iii) Contaminant mass within the epikarst and fractured rock; and, iv)Flow dynamics and contaminant transport mechanisms of the karst bedrock. The complexity of karst environments also creates challenges for selecting and implementing appropriate remedial technologies. Remediation of contaminated soils can be achieved through removal or in-situ treatment; however, remediation of contaminant mass in epikarst, solution-enlarged bedding planes, and deeper karst conduits remains challenging. Several case studies from KY UST sites demonstrate the critical importance of implementing surface and borehole geophysical technologies for characterizing karst hydrogeology and effectively remediating contaminant mass in karst systems. The case studies describe surface geophysics technologies (e.g. two-dimensional electrical resistivity imaging, refraction microtremor, frequency domain electromagnetic conductivity, very low frequency electromagnetics, etc.) and borehole geophysical methods (e.g. caliper, gamma log, borehole resistivity, optical televiewer, acoustic televiewer, heat-pulse flowmeter, etc.) used to adequately characterize and effectively remediate karst features serving as reservoirs and preferential contaminant transport pathways at KY UST sites.