Investigating the Effects of Natural Environmental Factors on the Viability of Dye Tracer Testing

Dye tracer tests that use granular activated carbon (GAC) to passively detect dyes in water flowing through wells, springs, and streams offer a semi-quantitative method of characterizing flow paths in karst aquifers. Because dye tracer testing is done in the field, there are many environmental factors that could impact the adsorption of dye to GAC. This study aims to investigate the kinetic properties of dye adsorption, determine whether or not naturally-occurring tannic acid affects the sorptive capacity of dye onto GAC, and measure the impact of pH upon dye adsorption onto GAC in a controlled lab setting using batch reactors and mixed flow reactors. Our results provide insight into the competitive adsorption that fluorescent dyes may experience in natural aquifer systems, thus putting quantitative constraints on processes that could inhibit dye adsorption and lead to false negatives in dye tracer tests. Results show that uranine dye adsorbs to GAC exponentially, following the first order rate law. GAC packets interacting with 20 ppm uranine dye are not susceptible to competitive adsorption with tannic acid, but more research needs to be conducted to determine if tannic acid can hinder concentrations near 500 ppb. Dye-water solutions with pH values near 4.5 have an inhibitory effect on adsorption due to the pH-dependent functional groups of both dye and GAC molecular structures. This research helps hydrogeologists working in karst environments understand some of the shortcomings of dye tracer testing in uncontrolled field environments