Time‐lapse laboratory tests to monitor multiple phases of DNAPL in a porous medium

Abstract

A B S T R A C TA soil contaminated by dense non-aqueous phase liquids generally exhibits variation of electrical permittivity and resistivity over time. In this paper, we relate photo images with results of electrical resistivity tomography, induced polarization tomography, and ground-penetrating radar survey in a laboratory-controlled test, where a cell, filled with grained-glass beads contaminated with HFE-7100 (hydrofluoroether) and under saturated conditions, was used. The aim was to find robust links between geophysical and physico-chemical parameters of a contaminated soil in order to reduce the ambiguities in data interpretation. The monitoring, conducted over 100 days, shows that each geophysical method may or may not be sensitive to the multiple phases of hydrofluoroether (pure, dissolved and gaseous phases) depending on the contaminant (chemical composition, fresh, mature, etc.) and on the host enviroment. We propose some empirical relationships that allow us to quantitatively monitor the water saturation variation induced by hydrofluoroether.The photo images confirm that the pure phase of hydrofluoroether changes over time, which is probably due to biological or/and chemical variation of the contaminant. Electrical resistivity tomography results appear to be sensitive to the vast amount of pure phase of the hydrofluoroether. Induced polarization, measured in the extremely low frequency range (<25 Hz), allows detecting the pure phase of the contaminant, probably due to the decrease of water permeability and chemical degradation of the compound over time. The ground-penetrating radar and time domain reflectometry methods based on measurements in very-high frequency and ultra-high frequency ranges are mainly sensitive to the water content and, as a consequence, to the replacement of water by pure and gaseous phases of hydrofluoroether.

Complex Electrical Resistivity and Dielectric Permittivity Responses to Dense Non-aqueous Phase Liquids' Imbibition and Drainage in Porous Media: A Laboratory Study

“…The use of GB also prevents the occurrence of unexpected phenomena such as adsorption during the experiment. The relative permittivity of a GB pack is 5.9 (Orlando and Palladini, 2019). The complex resistivity of the medium was measured with SIP using SIP-lab IV manufactured by Radic Research in Germany.…”

Experimental study of electrical complex resistivity in a 2D multiphase porous medium under non‐isothermal conditions: Application to soil remediation monitoring

“…(2014). Orlando and Palladini (2019) carried out a series of laboratory tests to study how resistivity and permittivity vary in a 2D cell in a multiphase (two‐phase) system. The contamination they used was HFE‐7100 (hydrofluoroether) in saturated (with pure, dissolved and gaseous phases) grained GB porous media.…”

“…In another study, Orlando and Renzi (2015) studied how electrical resistivity varies in ground due to the existence of DNAPL in a laboratory study. Like Orlando and Palladini (2019), they used a GB‐packed medium contaminated with HFE‐7100 in a saturated condition. They found that different DNAPL phases have different impacts on the physico‐chemical characteristics of the contaminated medium.…”