Abstract
A numerical model was developed to investigate contaminant transport and the concentration-control performance of groundwater circulation wells (GCWs) in a heterogeneous porous-fractured aquifer beneath a landfill site. The effects of aquifer structure, injection-extraction rate, and well configuration on contaminant plume evolution and simulated concentration responses were evaluated. Results showed that aquifer heterogeneity controlled contaminant migration patterns. In fracture-free media, plume evolution was mainly governed by regional groundwater flow and advective-dispersive transport, whereas fractures promoted preferential transport, earlier breakthrough, and greater spatial variability in contaminant distributions. Increasing the injection-extraction rate enhanced circulation-induced hydraulic gradients and promoted mean concentration reduction under the simulated conditions, with a more pronounced response in fractured media. The single-borehole vertical circulation well provided less extensive plume-scale concentration control than the evaluated multi-well configurations. However, comparisons among configurations with different numbers of boreholes reflect the combined effects of well number, spatial arrangement, and individual well flow-rate distribution. The simulated concentration reductions resulted from groundwater extraction, prescribed clean-water injection, hydraulic flushing, and solute redistribution, rather than an equivalent percentage of contaminant mass removal or destruction. These findings indicate that concentration-control performance is jointly influenced by aquifer heterogeneity, preferential flow structures, and circulation-induced hydraulic conditions. They also provide a numerical basis for the preliminary evaluation of GCW configurations and operating scenarios, supporting more informed groundwater pollution-control planning and sustainable management of landfill-affected aquifers.