Evaluation of key control factors on pollutant migration by suspended cutoff walls in contaminated sites

This study develops a two-dimensional numerical model for seepage and pollutant transport in sites with suspended cutoff walls, grounded in the advection-dispersion equation. The impacts of key factors, including the pressure head of the pollution source, the site's horizontal hydraulic gradient, and the horizontal distance between the downstream wall and the pollution source, on the non-linear seepage distribution and the wall's anti-pollution performance were investigated. Centrifuge model tests were conducted to confirm the numerical model's dependability. Furthermore, the concentration at the downstream wall bottom reaching 10% C₀ was established as the threshold for identifying the suspended containment system's failure. The research findings demonstrate that modifications to the site flow field due to parameter changes are a significant factor contributing to the macroscopic variations in pollutant migration. As the pressure head of the pollution source diminishes from 1.2 m to 0.3 m, the peak flow velocity at the mid-point of the liner bottom reduces by 25.6%, while the service life of the wall extends by 51.1%. The site flow-field distribution is significantly impacted, with the wall's service life increasing by 209.1% and 22.8%, respectively, as the site's horizontal hydraulic gradient decreases from 0.04 to 0.01 and the horizontal distance between the downstream wall and the pollution source increases from 4 m to 16 m. Therefore, the design of suspended cutoff walls in risk control of contaminated sites with deeply buried aquitards should focus on aspects related to these three factors.