Speaker
Description
Non-aqueous phase liquid (NAPL) contamination is among the most persistent and challenging forms of subsurface pollution, posing long-term risks to groundwater resources and ecosystem health. In particular, Dense Non-Aqueous Phase Liquids (DNAPLs) are difficult to detect and monitor due to their low mobility, strong capillary trapping, and density greater than water, which promotes downward migration and accumulation in heterogeneous subsurface environments. These characteristics complicate both the delineation of contaminated zones and the assessment of remediation efficiency. Electrical resistivity–based geophysical methods, and Induced Polarization (IP) in particular, provide a non-invasive approach to characterize NAPL distribution and monitor its temporal evolution in the subsurface.
This study first presents a coupled numerical framework designed to improve the interpretation of resistivity and IP responses associated with DNAPL migration during both contamination and remediation phases, with emphasis on early-stage depollution through pumping. A fully coupled three-dimensional model was developed to simulate DNAPL multiphase flow and its associated complex electrical resistivity response. The simulations were implemented by integrating Darcy-scale multiphase flow with electrical current propagation governed by frequency-dependent resistivity. Saturation-dependent petrophysical relationships were employed to link DNAPL content to both the in-phase (real) and quadrature (imaginary) components of electrical resistivity.
Model results were validated against independent laboratory IP measurements and image-based observations obtained from two-dimensional tank experiments. The simulations reproduce the observed IP response with high accuracy in regions characterized by relatively low DNAPL saturation, particularly within the cone of depression generated under pumping conditions. In contrast, zones with high DNAPL saturation exhibit larger discrepancies in the simulated in-phase resistivity, indicating limitations of conventional petrophysical formulations under strongly nonlinear saturation regimes. The quadrature resistivity response, however, shows greater sensitivity to highly contaminated zones and provides a sharper delineation of the DNAPL migration front, highlighting its superior potential for monitoring both the extent and intensity of DNAPL contamination. Despite these limitations, the coupled IP–multiphase modeling approach offers enhanced spatial and temporal insight into DNAPL behavior compared to conventional surface or borehole measurements, enabling a cost-effective and efficient framework for monitoring contamination and remediation processes.
To complement the DNAPL analysis, the study also addresses the highly dynamic behavior of Light Non-Aqueous Phase Liquids (LNAPLs) at the water table, where migration is strongly controlled by groundwater-level fluctuations and the interaction of three immiscible phases: water, LNAPL, and air. A combined experimental–numerical methodology was implemented using Time Domain Reflectometry (TDR) measurements in controlled laboratory tank experiments. TDR probes installed at multiple locations within a quasi-two-dimensional tank were used to monitor bulk dielectric permittivity under imposed boundary conditions simulating water table rise and fall. These measurements were converted into phase saturations and subsequently incorporated into multiphase flow simulations. Key hydraulic parameters, including relative permeability exponents and entry pressures, were estimated directly from the temporal experimental data.
Overall, the results demonstrate the strong potential of electrical geophysical methods, when integrated with multiphase flow modeling and laboratory calibration, to improve the detection, characterization, and monitoring of NAPL contamination across a range of subsurface conditions.
| Country | France |
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