This paper presents a formulation to incorporate the influence of water salinity on the swelling behaviour of a MX-80 bentonite into previously developed hydro-mechanical models that can reproduce swelling under dilute conditions. The effects of salinity on macro-and microstructural water chemical potentials were introduced. In addition, a description of solute transport was included to characterise the evolution of the system's salinity. A simplified geochemical model was adopted to idealise the geochemical complexity of bentonite. In addition, the modelling of the destructuration process that occurs during swelling was modified to account for the effect of salinity. The formulation was implemented in a multiphysics partial differential equation finite element solver, and the numerical model was used to simulate several vertical free swelling tests with feed water of different salt contents (deionised, 10, 35 and 70 g/L). The results demonstrate that even though the model can be developed further, it represents a significant improvement over models that do not account for the effects of salinity.

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Models of electrokinetic soil remediation systems have been developed significantly in recent decades. A wide range of physicochemical phenomena occurs in this type of process, which makes it difficult to capture all of the system's complexity in a model. Therefore, existing models do not attempt to simulate the behaviour of the entire geochemical system of natural soils and their porewaters but rather focus on the pollutant compounds of interest. This paper proposes a conceptual and numerical model that includes geochemical speciation other than the phenomena that have been described by other authors. In addition, a comparative modelling exercise is performed with a composition of natural porewater and a simplified equivalent composition. The results show that the buffering system of carbonates affects the temporal evolution and spatial distribution of the pH. Because the pH controls many of the phenomena that occur during this type of remediation, simulations using realistic geochemical systems are critical.

This study focuses on the evaluation of the Electrokinetic Soil Flushing (EKSF) strategy to remediate soil following a simulated spill of the herbicide oxyfluorfen. EKSF is attained by placing (in the soil mockup) two rows of electrodes of different polarity facing each other. The results are compared with those obtained in a reference experiment in which the same spill was simulated and no remediation actions were taken. In addition to the daily monitoring of the most important parameters in the flows, after the remediation test, a post-mortem analysis was performed to obtain a 3-D map of the pollutant distribution. Those results demonstrate that despite the hydrophobic character of oxyfluorfen, it can be efficiently transported by EKSF. Hence, after 34 days of treatment, a 26.8% improvement in the removal of oxyfluorfen was achieved (explained in terms of the effect of the electric field on the pollutant) compared with the reference experiment 2 in which only volatilization can explain the removal of the herbicide. Comparison of the removal of oxyfluorfen by EKSF with that of 2,4-D (studied in a previous study) demonstrates that comparable dragging to the cathode and volatilization are obtained. However, the lower efficiency of the transport of oxyfluorfen by gravity fluxes and electromigration (explained because it is contained as micelles) yielded worse performance of EKSF for this water-insoluble pesticide and hence less efficient remediation. This contradictory result reveals the importance of tests at large-scale facilities such as that used in this work to predict the performance of real systems in future full-scale applications.