Roles of leakage-induced advection and membrane-controlled transfer in reaction-chain contaminant transport through composite geomembrane cut-off walls: A reaction-chain transport framework and field application.

Persistent groundwater contamination from leakage through defective composite geomembrane cut-off walls (CGCWs) challenges long-term control, yet existing models often omit the coupled effects of leakage-induced advection, membrane-controlled transfer, rate-limited sorption, and sequential degradation, while representing transport using single-component or equilibrium-sorption formulations. Accordingly, this study develops a reaction-chain CGCW framework for multi-species transport in a wall-geomembrane-aquifer system with time-dependent non-uniform sources. The framework was validated against numerical simulations and a reduced analytical solution, then was applied to the PCE-contaminated Farmingdale Plaza Cleaners OU-2 site to evaluate long-term breakthrough of tetrachloroethene (PCE), trichloroethene (TCE), and cis-1,2-dichloroethene (1,2-DCE). Results show that leakage-induced Darcy velocity dominates CGCW performance; reducing it from 1.0 × 10-8 to 1.0 × 10-11 m/s lowers the 100-year relative PCE concentration by nearly three orders of magnitude. Moreover, lower membrane-controlled transfer strengthens containment, whereas wall sorption and kinetic mass transfer regulate retention-release behavior. Sequential degradation reduces parent-contaminant breakthrough but transfers risk to daughter products. Sobol analysis further shows leakage dominance for PCE and TCE, whereas 1,2-DCE is more sensitive to interactions among leakage, degradation, and wall sorption. This framework supports comparative CGCW assessment and computationally efficient preliminary screening.