Regional Flow Influenced Recirculation Zones of Pump-and-Treat Systems for Groundwater Remediation with One or Two Injection Wells: An Analytical Comparison

As a widely employed method for in situ remediation of groundwater contamination, the pump-and-treat (PAT) system involves the management of water recirculation between the extraction and injection wells. The recirculation zone (RZ) of an extraction-injection well pair in a confined aquifer has been well known. However, PAT systems are more frequently used in unconfined aquifers with a natural regional flow and may not only include one injection well. We develop comparable analytical models for an unconfined aquifer treated by two different system settings, including an extraction well and one injection well (1e/1i system) or two injection wells (1e/2i system). The role of regional groundwater flow is highlighted. Analytical solutions of RZs and recirculation ratios are obtained using complex potential functions, with a new treatment of the jump of the stream function at a branch cut. Results indicate that the shape of RZs and the recirculation ratio nonlinearly depend on several dimensionless parameters linked to the pumping rate and direction of regional flow. Compared to the 1e/1i system, the two injection wells in the 1e/2i system may reduce the integrity of RZs and decrease the recirculation ratio; however, they lead to a higher allowable pumping rate in satisfying the limitations of the water table in wells. This study suggests a useful methodology for analyzing PAT systems with multiple injection wells and provides new insights into RZs between extraction and injection wells.