f INTEGRATED, STUDENT-LED HYDROGEOPHYSICAL INVESTIGATIONS AT A SUSPECTED CENTRAL TEXAS SINKHOLE

A suspected sinkhole (Quadborder Sink) with unknown hydrogeological significance in a central Texas metropolitan area provided a research topic that was addressed by a group of graduate and undergraduate students during a semester-long hydrogeophysics class. These students designed geophysical field experiments using frequency-domain electromagnetic induction, electrical resistivity, groundpenetrating radar (50 and 100 MHz), microgravity, and seismic refraction methods, acquired data at the field site over multiple weekends, processed data, presented field results in weekly classes, and integrated results in a jointly written, comprehensive class report. Each of the methods provided useful information to establish the likely presence of a sinkhole and its lateral extent, the thickness and lithologic character of the sinkhole fill, the possible presence of an underlying shallow void in this karstic area, likely areas of preferential hydrologic recharge, and the character of the shallow interface between clastic fluvial and lacustrine fill and carbonate bedrock. Strengths of the approach included application of multiple geophysical methods to a single hydrogeologic problem of concern to residents and a local governmental agency. Weaknesses included the inability to spend adequate time and effort to apply advanced processing steps to the datasets acquired using different methods and maximize the benefits of multiple geophysical approaches to a common problem.