Time domain induced polarization monitoring for enhanced remediation of DNAPLs during in-situ microemulsion flushing

Abstract

In-situ microemulsion flushing has been considered a development potential technology for remediating aquifers contaminated by dense non-aqueous phase liquids (DNAPLs) via increasing the apparent solubility and reducing the interfacial tension. Normally, monitoring wells are established in the remediation area for tracking the spread of injectant and the removal of DNAPLs. On this basis, alternating time domain induced polarization (TDIP) measurements and injection/pumping operations were conducted at a CHCl3-contaminated weathered andesite site. Full-decay TDIP data were inverted and correlated with groundwater sampling to reflect contaminant solubilization and reagent distribution. Interpretation results demonstrated that TDIP provided spatially continuous electrical imaging in the entire remediation volume, capturing the footprints of CHCl3-contaminated groundwater and the remediation reagent. The injected reagent exhibited strong conductivity and polarization contrasts with contaminated groundwater, confirming its spread across most of the weathered andesite layer. Thresholds of m = 50 mV/V delineated CHCl3 contamination zones exceeding the regulatory limit of 300 µg/L. Reagent spreading along profiles revealed preferential flow paths within highly permeable fracture zones. Chargeability reduction is correlated with DNAPL desorption, showing over 90% removal efficiency in groundwater samples, although residual contamination persisted in heavily contaminated zones. Microemulsion flushing effectively enhanced DNAPL solubilization, while weathered andesite medium and excessively high injection velocity limited remediation effectiveness in this specific site. This study confirms TDIP as a promising tool for DNAPL contaminant distribution mapping and real-time remediation monitoring, supporting more efficient and data-driven remediation strategies.