Application of Excitation-Emission Matrices to Fluorescent Dye Tracing of Groundwater Flow

Fluorescent dye tracing of groundwater is a technique employed particularly in carbonate rock karst regions to examine karst hydrology by mapping underground flow paths. It is important to understand the hydrology of karst environments because solutionally-enlarged conduits may allow the rapid influx of contaminants into the groundwater system. Fluorescent dye tracing involves the injection of a fluorescent dye into an appropriate injection site (sinking streams, sinkholes, or even through soil flushed with water) and is followed by sampling at sites where the dye may be recovered (typically springs). Various methods exist by which sampling may occur, but all methods ultimately result in laboratory analysis of samples through the application of fluorescence spectrophotometry. In Western Kentucky University’s Crawford Hydrology Laboratory, twodimensional synchronous scanning is applied to aqueous samples that potentially contain fluorescent dyes to quantify the concentration of the dye in the sample and thus determine flow paths between dye injection and recovery sites. Sometimes this analysis is impeded by complications, including background fluorescence and challenges associated with concurrent use of multiple fluorescent dyes. This research explores potential solutions to these issues through the application of three-dimensional synchronous scanning. Both two and three-dimensional synchronous scanning were applied to collections of dilutions of the fluorescent dyes, fluorescein (FL), eosin (EO), rhodamine WT (RWT), and sulphorhodamine B (SRB), as well as a collection of anthropogenically-impacted water samples pulled from the Lost River Groundwater Basin in Bowling Green, Kentucky, following the injection of FL. Although measurement of dye concentration proves to be challenging, three-dimensional synchronous scanning provides an additional method to distinguish FL from EO in aqueous water samples and an additional method by which it may be determined if a particular dye compositionally dominates a sample that contains more than one fluorescent dye. Furthermore, through this study, a preliminary characterization of the background fluorescence of the Lost River was conducted; a preliminary parameter set for the three-dimensional analysis of the fluorescent dyes, FL, EO, RWT, and SRB was developed; and preliminary spectral fingerprints were developed for the fluorescent dyes, FL, EO, RWT, and SRB