COMBINING QUANTITATIVE DYE-TRACING WITH GEOPHYSICAL METHODS TO UNDERSTAND KARST CONDUIT FLOW SYSTEMS

Geophysical methods such as direct-current electrical resistivity, electromagnetics (VLF), and gravity have been used for many years in investigations of karst lands, and recent improvements in electronics and modeling software have led to increasing use of these tools. Likewise, both quantitative and qualitative dye-tracing methods have also been used for many years in karst studies. Around the greater Springfield area, a Missouri metropolitan area, a number of combined studies over the past few years has offered deeper insight into the karst system than previously reported.

By using combined geophysical and dye-tracing methods to evaluate factors influencing groundwater movement through the shallow karst system in the Springfield area – combined with fortuitous timing related to weather events - it appears that shallow groundwater in the Springfield area occurs in discrete fractures and along bedding planes, with a significant input component from flow along bedding planes or other sub-horizontal features. Based on one unique trace, data suggest that dye traces may be affected by groundwater elevations, where crossover from one conduit system to another occurs under most water level conditions, but ceases under the lowest flow conditions. Deeper insight into local geophysical investigations has also been gained by the “feedback” loop of applying knowledge gained from dye-tracing to better interpret geophysical data. These combined methods were recently applied to a source investigation of groundwater contamination from an unknown site.