Evolution characteristics of remediation process of secondary contaminant sources of low-permeability lens driven by circulating well

In this paper, groundwater circulation well (GCW) was as used to remediate contaminant in low-permeability lens in aquifer, and a theoretical framework was constructed to describe the contaminant removal process in low-permeability lens driven by a GCW. In this theoretical framework, the evolution process of contaminant removal rate in low-permeability lens is summarized in a sequence of evolution stages in which several critical states and conditions are defined. Using oxytetracycline (OTC) as a representative contaminant, a finite-element numerical model based on COMSOL Multiphysics is established considering adsorption and biodegradation of the secondary contamination of groundwater. The theory is verified, and the parameter sensitivity analysis of the theory prioritize different factors influencing the contaminant removal process. The results are summarized as follows. The evolution process of contaminant removal rate driven by advection, hydrodynamic dispersion and adsorption includes four stages (initial stage, rising stage, falling stage and complete removal stage), and the evolution process of contaminant removal rate driven by biodegradation includes three stages (initial stage, falling stage and complete removal stage). The evolution paths of contaminant removal dominated by adsorption or biodegradation in the first stage were established, and they were divided into four categories (one-stage, two-stage, three-stage and four-stage evolution paths), totaling 22 evolution paths. Four evolution stages dominated by advection, hydrodynamic dispersion, adsorption and biodegradation were defined, and the critical states and conditions were defined. The influences of hydrodynamic parameters and solute transport parameters on evolution stage and critical moment are analyzed in details.