THE USE OF MULTIPLE TRACERS TO ASSESS FATE AND TRANSPORT PROPERTIES IN A KARSTIFIED LIMESTONE MODEL (Invited Presentation)

The same characteristics that make karst groundwater systems highly productive make them very vulnerable to contamination. Because these systems serve as important sources of freshwater for human consumption and ecologic integrity, karst water may also serve as a potential source of contaminant exposure. The heterogeneous and anisotropic complexity of karst aquifers make them very difficult to characterize for accurate prediction of contaminant mobility and persistence, and impose tremendous challenges on the detection and remediation of contaminants in these systems. Characterization and quantification of flow and transport processes at field-scale is limited by low resolution of spatiotemporal data. Studies at the laboratory scale can provide fundamental knowledge on characterization and quantification tools that can be applied at the field scale to enhance resolution. This work employs the injection of multiple tracers in an intermediate karstified lab-scale physical model (IKLPM) to assess spatially-variable fate and transport (F&T) processes in karst systems. Two-dimensional temporal concentration distributions (TCDs) obtained from calcium chloride, uranine, and rhodamine wt tracer experiments in the IKLPM are analyzed using the method of moments and CXTFIT Mobile-Immobile Model to characterize and quantify fate and transport parameters in the system at various scales and flow rates. TCDs showed variability associated with differences in the dominant processes affecting the F&T of the tracers. The estimated F&T parameters for the tracers revealed high spatial variability related to preferential flow heterogeneities and scale dependence. Advective transport is rapid, but focused in a small volume of the karstified model. Transport between the mobile and less mobile domains is characterized by low mass transfer coefficients. Future work will integrate the experimental methods at spring-watershed scales for enhanced characterization of F&T processes in karst systems of eogenetic character. The development of these technologies will improve our ability to predict fate and transport of contaminants in these systems and reduce impacts to the environment and human health.