Experimental study of conservative solute transport in heterogeneous aquifers

Aquifer heterogeneity affects the characteristics of solute breakthrough curves (BTCs). A better understanding of the relationship between aquifer heterogeneity and BTCs will help improve prediction of the fate of contaminants in an aquifer. Previous studies have shown that systematic research of aquifer heterogeneity on solute transport is limited. Therefore, this study investigates the impacts of aquifer heterogeneity on conservative solute BTCs and transport mechanism via experimental and modeling approaches. Tracer experiments are conducted in four flow-through columns exhibiting different patterns of heterogeneities. Furthermore, this study also examines the influence of hydraulic conductivity on transport mechanism. In addition, this paper analyses the correlation between hydraulic conductivity and dispersivity, which are the key parameters of conservative solute transport in an aquifer. Experimental data indicates the impacts of aquifer heterogeneity on transport of tracer. Tracer BTCs in a homogeneous aquifer have the typical sigmoid shape without tailing. In a heterogeneous aquifer, tracer BTCs display a strong and persistent tailing. In a preferential flow aquifer, tracer BTCs have pronounced tailing and early arrival time. The hydraulic conductivity of an aquifer significantly affects the transport mechanism of tracer. When the hydraulic conductivity is higher than 1.53 cm/min, transport of tracer is applicable to the ADE. When the hydraulic conductivity is lower than 1.53 cm/min, transport of tracer is applicable to the TRM. This work offers insight into the correlation between the hydraulic conductivity of an aquifer and the dispersivity of a conservative solute. A critical finding is that hydraulic conductivity K and dispersivity lambda correspond to an exponential regression form lambda = e (0.24555) + (4.54413K) + (2.27308K2) (R-2 = 0.957).