Predicting suitability of different scale-dependent dispersivities for reactive solute transport through stratified porous media

Abstract

In this paper, the behavior of breakthrough curves (BTCs) for reactive solute transport through stratified porous media is investigated. A physical laboratory model for layered porous media was constructed, in which thin layer of gravel was sandwiched in between two thick layers of natural soil. Gravel layer and natural soil layers were hydraulically connected as single porous continuum. A constant source of tracer was connected through gravel layer and elucidated at different sampling points in the direction of flow. Flexible multiprocess non-equilibrium (MPNE) transport equation with scale-dependent dispersivity function was used to simulate experimental BTCs of reactive solute transport through layered porous media. The values of equilibrium sorption coefficient and other input parameters were obtained experimentally. The simulation of BTC was performed using MPNE model with scale-dependent dispersivity. The simulation of different scale-dependent dispersivities was then compared and it was found that for field scale of estimation of dispersivity, asymptotic and exponential dispersivity functions performed better. In continuation to the comparison of simulated BTCs obtained using different models, spatial moment analysis of each aforesaid scale-dependent dispersivity model was also done. Spatial moment analysis provides the information related to mean solute mass, rate of mass travel, and mean plume dispersion. Linear and constant dispersivities showed higher variance as compared to asymptotic and exponential dispersion functions. This supports the field applicability of asymptotic and exponential dispersivity functions. The BTCs were also found to elucidate a nonzero concentration with time, which was clearly affected by physical non-equilibrium. In natural condition, such information is required in effective aquifer remediation process.