THE REVOLUTIONARY IMPACT OF TRACER INVESTIGATIONS ON KARST HYDROGEOLOGY: A TRIBUTE TO NICHOLAS C. CRAWFORD (Invited Presentation)

Underground water in karst terrain is schizophrenic. It has the personality of ground water - sometimes - and the personality of surface water - at other times. Which personality it display depends on details of aquifer geology, aquifer history, and the magnitude of discharge. Nicholas Crawford, from his base at Western Kentucky University has made large contributions to understanding the karst water personality: a model for plateau margin karst, the application of geophysical methods, particularly microgravity, to the charactrization of karst aquifers, much pioneering work on the environmental impacts of karst, and the use of tracer dyes, a crude technique that he turned into a finely-honed instrument. Water tracing with fluorescent dyes has a long history, much of it consisting of dumping dye into a sinking stream and waiting to see which spring turned green. Invention of the charcoal dye detectior advanced the technique but it was really the introduction of automatic water samplers and quantitative dye concentration measurement by fluorescence spectroscopy that transformed the technique. As dye tracing became a central tool in environmental investigations, Crawford, among others, realized that tracer results would need scientific verification that would stand up in a Court of Law. Crawford, especially, introduced detailed protocols for dye injection, sample collection, chain-of-custody, laboratory procedures, and a check list of site investigations. Measurement sensitivity was improved by orders of magnitude and with it, the range of hydrological questions that could be probed.