Abstract: Soil-bentonite (SB) cutoff wall is commonly employed as a vertical barrier to prevent further leakage of landfill leachates. With this engineering background, based on the multi-solute transport framework, this study presents a theoretical model that can be used to evaluate the barrier performance of the SB cutoff wall considering the effects of prior contamination and source remediation. Three solutes are considered in this model, among which Na⁺ and Ca²⁺ are selected as non-characteristic pollutants, and a single organic pollutant is selected as the characteristic pollutant. Afterwards, the finite difference method is adopted to solve the model, and its rationality is verified by three comparative studies. Finally, taking toluene as the characteristic pollutant, the effects of different factors on the wall’s barrier performance are evaluated using the defined breakthrough time tB. The results show that an increase in the prior contamination time tP decreases tB, and the reduction rate of tB may reach 38.8% when tP is 2 a. However, the increase in the transition layer thickness lu has the opposite effect. An increase in the source concentration reduction parameter (S and a decrease in the source remediation initiation time tS both contribute to prolonging tB. Moreover, when S is large (e.g., greater than 0.61 a⁻¹), the wall may not be broken through by organic pollutants. Neglecting the presence of Na⁺ and Ca²⁺ may overestimate the service time of the SB cutoff wall by more than 47.0% compared with considering their presence. Under the same engineering condition, an increase in bentonite content increases the thickness of the bound-water film on the surface of soil-bentonite, which causes an increase in tB. In engineering practice, the SB cutoff wall can be designed by comprehensively considering the internal and external factors as well as the construction cost and service life requirements. Overall, this work can provide scientific guidance for the application of SB cutoff walls in anti-seepage and containment engineering of landfills.

Key words: SB cutoff wall, multi-solute transport, prior contamination, source remediation, theoretical model, barrier performance evaluation