Arsenic mobilization and recirculation dynamics: Groundwater circulation wells for enhanced decontamination in complex coastal aquifer environments

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Arsenic (As) contamination poses serious risks to groundwater quality and human health, with millions globally exposed to unsafe levels, making remediation a critical challenge. Coastal aquifers are especially vulnerable due to heterogeneous lithology, saline intrusion, and complex hydrogeochemical dynamics, which limit the effectiveness of conventional pump-and-treat (P&T) systems and call for innovative remediation solutions. This study evaluates groundwater circulation wells (GCWs) as a technology to mobilize and remove As, focusing on the development of the GCW-induced recirculation cell. The research was conducted at a coastal industrial site with longstanding As pollution, representative of complex hydrogeology. A relational geodatabase integrated data from 76 boreholes, 41 piezometers, 2 multi-level sampling wells (MLSWs), and 1 GCW. A 3D stratigraphic model supported the design of a 23 m GCW with screened sections at 6÷8, 12÷15, and 19÷22 m. Groundwater was extracted, treated above ground, and reinjected to establish a recirculation cell. Hydrochemical and electrical conductivity (EC) monitoring over 550 days captured the spatial and temporal dynamics of As mobilization, removal, and salinity mixing. The GCW-induced recirculation cell mobilized As up to ∼9,000 μg/L—around 900 times the World Health Organization (WHO) guideline of 10 μg/L—before stabilizing at ∼6,500 μg/L. The system achieved 66% removal efficiency, extracting ∼80 kg of As while promoting groundwater mixing. EC data from MLSWs provided unprecedented insights into the spatio-temporal evolution of the recirculation process. These findings demonstrate that GCWs provide a viable and sustainable alternative to conventional remediation strategies for addressing persistent As contamination in complex coastal aquifers. • Groundwater circulation well (GCW) enhances arsenic (As) removal in coastal aquifer • 3D geomodeling and real-time monitoring advanced the understanding of recirculation • Groundwater mixing and saline wedge dynamic play a role in boosting As mobilization • As content and electrical conductivity measures reveal recirculation cell dynamics • Unprecedented insights into the evolution and spatial extent of recirculation cells