Seepage Migration Process of Soluble Contaminants in Porous Medium considering Adsorption History

By embedding a nonlinear nonequilibrium adsorption model considering the adsorption history (i.e., Bai model), a governing equation for the three-dimensional model is extended, which discussed the influence of varying seepage velocity and injection concentration. Compared with the previous linear adsorption model, the concentration peak value of the nonlinear nonequilibrium adsorption history model is higher than that of the linear model, and the time to reach the peak concentration is slightly earlier. In the case of horizontal seepage water, a pollution point source tends to migrate along the direction of water flow and has less ability to diffuse in the vertical direction. Compared with the adsorption history model, the linear model has a stronger blocking ability for pollutant migration, and the longer the time, the greater the gap between the two models. The longer the decay period, the wider the spread of contaminants, and the longer it takes for them to migrate out of the model completely. The more significant the head difference, the larger the diffusion area of pollutants in the main seepage direction, but it has no promotion effect on the lateral diffusion. The pollutant concentration is higher than that of the point source case, and the diffusion range in each section is wider. The closer it is to the center of the pollution source, the weaker the dispersion effect on the diffusion of pollutants in the main seepage direction, and the pollutants will spread in the countercurrent direction, causing pollution upstream.