Performance assessment of groundwater circulation well coupled with surfactant-enhanced flushing in low-permeability zones.

Groundwater contamination in heterogeneous aquifers has become a pressing global environmental challenge. In low-permeability zones, severe mass transfer limitation and strong contaminant adsorption significantly hinder the remediation efficiency of groundwater circulation well (GCW). However, the synergistic contaminant removal mechanism of GCW coupled with surfactant-enhanced flushing remains unclear, and systematic quantitative research on its key control parameters remains limited. This study aims to reveal the contaminant removal mechanism of this coupled system, quantify key control parameters, and propose targeted GCW design recommendations. A fully coupled numerical model integrating groundwater flow, solute transport and surfactant-modified dynamic adsorption-desorption processes was developed, and rigorously validated against three independent published experimental datasets. Results indicate that injection-extraction flow rate and lens permeability are pivotal factors affecting surfactant desorption efficiency. Increasing the injection-extraction flow rate from 50 m3/d to 100 m3/d significantly enhances GCW contaminant removal efficiency but reduces surfactant desorption efficiency from 39% to 27%. As lens permeability increases from 1 × 10-9 m/s to 1 × 10-7 m/s, GCW remediation performance improves continuously, while surfactant desorption efficiency first increases then decreases, peaking at 39% at 7.74 × 10-9 m/s. Screen configuration governs the hydraulic capture zone of GCW but does not significantly affect surfactant desorption. Specifically, rational GCW and well screen design aligning lenses with streamline-dense zones substantially improves contaminant removal efficiency. Comprehensive analysis of key factors yields contour maps of remediation and desorption efficiency, providing targeted guidance for GCW design under different operating conditions within this study's modeling.