Effects of karst conduit structure on breakthrough curves: Experiments and modeling

Due to the complexity of karst conduit systems, field tracer tests can produce a variety of breakthrough curves (BTCs) and present challenges in analyzing BTCs and determining solute transport pathways. In this study, tracer experiments were conducted in the laboratory using karst pipe structures such as asymmetric branch pipe and pool models to investigate the effect of karst conduit structure on BTC. Subsequently, experimental BTCs were simulated using the OM-MADE (One Dimensional Model of Multiple Adsorption, Diffusion, and Storage in Exchange Zones) model, and the results were compared with the experimental results. The results show that the main pipe in the branch pipe model significantly affects the number of BTC peaks, with increasing two-branch pipe spacing (D_L) leading to a decrease in peak concentration and delaying peak time. In the pool model, increasing the pool volume or number leads to lower peak concentrations and stronger tailing effects. In the continuous pool model, the outlet location has the most significant influence on the BTC morphology. The OM-MADE model accurately simulates the bimodal and trailing features of the BTCs (R² ≥ 0.9), demonstrating its reliability in predicting groundwater contamination. This study provides key insights that can help predict and manage groundwater contamination.