Numerical simulation study on solute transport in Karst aquifers under combined effects of dual conduit and pool

Breakthrough curves (BTCs) carried out in Karst aquifers often exhibit anomalous transport characteristics such as long tailing and multiple peaks.However, most existing studies have focused on the influence of single factors, making it difficult to understand BTCs with anomalous features resulting from multiple interacting factors.In this paper, two key factors—the length ratio of dual conduits and the pool size—were considered simultaneously.A finite element numerical simulation was employed to analyze the variations in peak time, peak height, tailing intensity, and peak separation under different conditions, thereby systematically investigating the combined effects of these two factors on BTCs.The results indicate that under a fixed length ratio, increasing the pool size causes the dual peaks to gradually merge and may lead to a distinctive pattern in which the first peak is lower than the second.For a fixed pool size, the retention effect of the pool weakens the separation between the dual peaks.When the pool size decreases while the length ratio increases, BTCs evolve from a single peak to dual peaks, with higher peak concentrations and reduced tailing.However, simultaneous increases in both pool size and length ratio significantly reduce peak concentrations and enhance curve broadening and tailing effects.These findings not only improve the theoretical understanding of anomalous transport in Karst aquifers but also provide new insights for interpreting BTCs, which may aid in predicting contaminant migration and supporting groundwater resource management.