Removable alginate gel barriers for contaminant source zone isolation in aquifer remediation: A bench-scale study

Non-aqueous phase liquids (NAPLs) in aquifers act as persistent sources of groundwater contamination, while conventional flushing and sparging methods often suffer from inefficient sweep and excessive reagent consumption. This study proposes a novel strategy to hydraulically isolate the contaminant source zone using a temporally constructed alginate gel barrier (AGB) to enhance remediation efficiency. A two-dimensional flow chamber model packed with a sand was used for this bench-scale study. The AGB was formed in the flow chamber by sequential injection of sodium alginate and thickener solutions, followed by Ca²⁺-induced crosslinking, and subsequently removed using a sodium-rich solution. A series of experiments were conducted to evaluate ozone sparging, surfactant flushing (SDS + n-butanol), and cosolvent flushing (ethanol) within the confined source zone containing either a dissolved contaminant (fluorescein) or NAPL (mixture; PCE/hexane/oil-soluble fluorescence agent). The AGB effectively confined gas and liquid flow to the target region, significantly improving contact between remedial agents and contaminants. Ozone sparging removed >96% of the fluorescence from the oil-soluble fluorescence agent dissolved in the NAPL, surfactant flushing eliminated >90% within 12 h, and ethanol flushing achieved >97% removal within 5 h, with 78% PCE recovery in the effluent. Notably, required reagent volumes were substantially lower than those estimated for full-domain treatment. These results demonstrate that temporary source-zone encapsulation using AGB can markedly reduce chemical usage while enhancing remediation performance in NAPL-contaminated aquifers.