Spatiotemporal characteristics and hydrogeochemical evolution of toluene and trichloroethylene composite contamination zones in groundwater.

The synergistic and antagonistic interactions between groundwater composite contamination plumes result in complex and dynamically evolving pollution effects, complicating the formulation of investigation and remediation strategies. This study employed a mesoscale tank system with high environmental fidelity to simulate the migration and transformation processes of dissolved-state toluene and trichloroethylene composite plumes, analyzing their biogeochemical succession. Findings indicate convergence at plume margins, forming persistent composite contamination zones. Toluene degradation rapidly depletes oxygen, creating anaerobic conditions while serving as an efficient carbon source that stimulates proliferation of characteristic microorganisms. Concurrently, molecular hydrogen generated during degradation provided a sustained electron acceptor source, promoting TCE reduction and dechlorination at rates 2.35-4.34 times higher than in single-pollutant zones. Combining intermediate product identification, differentiated degradation pathways for toluene and trichloroethylene were established, regulated by biogeochemical mechanisms. This study elucidates the succession of pollution dynamics within the composite zone, driven by thermodynamic succession of electron acceptors, transitioning from aerobic antagonism to anaerobic synergy. These findings underscore the imperative to integrate redox evolution models with pollutant migration processes to accurately predict the fate of mixed plumes and formulate remediation strategies.