An analytical model for solute transport in a large-strain aquitard affected by delayed drainage

This paper proposed a model for solute transport in a large-strain aquitard coupling effects of diffusion, adsorption, and consolidation processes. The analytical solutions describing the drawdown and solute transport in the aquitard were derived under the condition of variable drawdowns in adjacent confined aquifer. The breakthrough time (BTs) of solute transport in the large-strain aquitard (LD model) was analyzed, and compared with that of the rigid porous medium (ND model) before consolidation, and the equivalent rigid porous medium (NDf model) at end of the consolidation, respectively. Results reveal that greater Darcy flow velocity, stronger solute diffusivity, and weaker adsorption of soil particles result in shorter BTs of solute transport in the large-strain aquitard, and the impacts of specific storage and void ratio on the BTs are influenced by the adsorption of soil particles. Compared with the ND model, the delayed drainage accelerates solute transport with weak adsorption, while it has the opposite effect with strong adsorption. BTs predicted by the LD model is always smaller than that of the NDf model. It is also found that the larger leakage coefficient of the aquitard significantly enlarges the difference of BTs between the NDf and LD models (Delta t), and the consolidation factor of the aquitard is positively correlated with the Delta t. The ratio of Delta t over the BTs of the LD model has a linear positive relationship with the average cumulative water release of the per unit volume aquitard under the fixed drawdown in the adjacent confined aquifer.