Analytical model for contaminants transport in triple composite liners with depth-dependent adsorption process

Predictions of contaminant transport in landfill composite liners are essential to assess the risk of groundwater pollution. The amount of soil organic carbon is strongly depth-dependent, which plays a crucial role in the adsorption of organic contaminants and heavy metal ions. The one-dimensional analytical model of contaminant transport in the triple composite liner consisting of geomembrane, geosynthetic clay liner and attenuation liner is presented considering the influence of depth-dependent adsorption coefficients. A specific sigmodal function is introduced to describe the attenuation of adsorption coefficients along the depth. The solution is obtained by the Laplace transformation. The analytical model was validated by experimental and numerical results. The results of the sensitivity analysis show that depth-dependent adsorption coefficients are critical for the risk assessment of groundwater pollution. The breakthrough time of composite liners can be overestimated by a folder of 2.5 with constant adsorption coefficients. The effects of parameters related to the depth-dependent adsorption process on the long-term transport of contaminants are critical for the design of a stable and effective composite liner system The proposed solution can capture the field observed data well and is consistent with the field observation. In addition, the proposed analytical solution may serve as a benchmark for various numerical models.