Groundwater Circulation Well Test for Synergistic Remediation of a Heterogeneous Site: Extraction, Tracing and Oxidation

Field tests were conducted at a heterogeneous industrial site using one circulation well and six monitoring wells. Groundwater circulation well (GCW) extraction–injection (30 d), multi-component tracing (6 h), and circulation–oxidation (20 h) tests were performed to investigate the flow-field characteristics and their influence on multi-component solute transport. The results suggested that the extraction–injection circulation mode increased the flow rate of the single well from 0.5 m3/h to 3.5 m3/h, establishing a composite flow field with near-field circulation and far-field outward expansion. Short-term circulation achieved limited concentration attenuation primarily near the well with rebound. Long-term circulation elevated the average concentration attenuation rates of benzene from 13% in the short-term test to 61%, and chemical oxygen demand (COD) from 16% to 47%, expanding the remediation scope of the circulation well. Bromide tracer tests and an advection–dispersion equation characterized the heterogeneous flow field with preferential flow channels and slow migration zones. Furthermore, sulfate tracer transport was governed by adsorptive retardation and advective delivery. Circulation–oxidation tests showed that benzene and COD showed higher concentration attenuation than naphthalene. After cessation, benzene and COD concentration attenuation rates increased by 39% and 29% compared to the short-term test without oxidation. Electrical resistivity tomography (ERT) revealed the downward diffusion of the oxidant, suggesting that the circulation well system enhances oxidant transport and expands the oxidant-affected zone. This research provides field-scale diagnostic evidence and in situ diagnostic methodologies for GCW remediation at complex contaminated sites.