GEOPHYSICAL FIELD STUDY OF KARST AND SOLUTION FEATURES NEAR AN AGGREGATE SITE IN ALABAMA

Carbonate-bearing rocks underlie large parts of Alabama and other southeastern states. Chemical dissolution of these strata dramatically alters their hydrologic properties, such as permeability, storativity and transmissivity. Karst features, such as solution-enlarged fractures and conduits, serve as major pathways for movement of water and contaminants in crystalline rocks. Here, we present results of a study aimed at developing tools for characterizing karstic aquifers and advancing the development of conceptual and numerical models of how karst features influence water levels and groundwater flow on field scales of <5 km. The project centers on work at a field site in Spring Villa, Alabama, where significant activation of a karst system has recently developed in the Chewacla Marble, which has been dewatered and mined for aggregates since the early 1900's. Damage to residential property and road closures have resulted in extensive litigation over the last 5 years, and over 100 sinkholes in nearby areas have been reported. In this study, we use ground conductivity surveys and electrical resistance tomography (ERT) to image subsurface fractures, conduits and developing sinkholes at the field site. We compare the imaging results to sinkhole remediation excavations in an effort to improve anomaly interpretation and to understand the geologic and hydrologic controls on sinkhole formation.