Quantifying Reagent Spreading by Cross-Borehole Electrical Tomography to Assess Performance of Groundwater Remediation

TY - JOUR

T1 - Quantifying Reagent Spreading by Cross-Borehole Electrical Tomography to Assess Performance of Groundwater Remediation

AU - Lévy, Léa

AU - Thalund-Hansen, R.

AU - Bording, Thue Sylvester

AU - Fiandaca, Gianluca

AU - Christiansen, Anders Vest

AU - Rügge, Kirsten

AU - Tuxen, Nina

AU - Hag, M.P.

AU - Bjerg, P.L.

PY - 2022/9

Y1 - 2022/9

N2 - In situ remediation of contaminated groundwater often relies on the installation of a treatment zone (TZ) degrading the contamination. Zero-valent-iron (ZVI) is a type of reagent used for this purpose. Adequate delivery of ZVI in the whole target volume is particularly challenging and requires monitoring with high spatial resolution. We present a monitoring tool for imaging the dynamic spreading of ZVI and its associated ionic cloud, using cross-borehole time-lapse electrical resistivity tomography (ERT). This tool works in urban areas and is particularly suitable for achieving the required spatial resolution at the scale of the target volume. Groundwater and sediment samples show a consistent spatial and temporal distribution of the remediation cloud with cross-borehole ERT. Yet, the 2D anomalies observed with cross-borehole ERT provide a more spatially complete and rapid image of the remediation cloud distribution than if based solely on monitoring screens. At the study site, ZVI injection leads to uneven spreading, clearly documented by cross-borehole ERT monitoring. The benefit of hydraulic conductivity (K) mapping by cross-borehole induced polarization (IP) to understand unexpected injection paths (upstream leakage, spreading in preferred pathways) is investigated. A 2D, IP-based, continuous, and coherent K-distribution is obtained that compares well with estimations by grain size analyses from the TZ. However, the IP-based K-field fails at predicting injection paths, suggesting the creation of pathways during the high-pressure injection of ZVI. Cross-borehole time-lapse ERT is the most promising geophysical tool for performance assessment of in situ remediation involving reagents with conductivity contrast.

AB - In situ remediation of contaminated groundwater often relies on the installation of a treatment zone (TZ) degrading the contamination. Zero-valent-iron (ZVI) is a type of reagent used for this purpose. Adequate delivery of ZVI in the whole target volume is particularly challenging and requires monitoring with high spatial resolution. We present a monitoring tool for imaging the dynamic spreading of ZVI and its associated ionic cloud, using cross-borehole time-lapse electrical resistivity tomography (ERT). This tool works in urban areas and is particularly suitable for achieving the required spatial resolution at the scale of the target volume. Groundwater and sediment samples show a consistent spatial and temporal distribution of the remediation cloud with cross-borehole ERT. Yet, the 2D anomalies observed with cross-borehole ERT provide a more spatially complete and rapid image of the remediation cloud distribution than if based solely on monitoring screens. At the study site, ZVI injection leads to uneven spreading, clearly documented by cross-borehole ERT monitoring. The benefit of hydraulic conductivity (K) mapping by cross-borehole induced polarization (IP) to understand unexpected injection paths (upstream leakage, spreading in preferred pathways) is investigated. A 2D, IP-based, continuous, and coherent K-distribution is obtained that compares well with estimations by grain size analyses from the TZ. However, the IP-based K-field fails at predicting injection paths, suggesting the creation of pathways during the high-pressure injection of ZVI. Cross-borehole time-lapse ERT is the most promising geophysical tool for performance assessment of in situ remediation involving reagents with conductivity contrast.

KW - groundwater remediation

KW - monitoring

KW - electrical resistivity

KW - cross-borehole

KW - IN-SITU REMEDIATION

KW - ZEROVALENT IRON PARTICLES

KW - INDUCED POLARIZATION

KW - RESISTIVITY TOMOGRAPHY

KW - PERMEABILITY PREDICTION

KW - FREQUENCY-DOMAIN

KW - CONDUCTIVITY

KW - SAND

KW - NANOPARTICLES

KW - SURFACE

U2 - 10.1029/2022WR032218

DO - 10.1029/2022WR032218

M3 - Journal article

SN - 0043-1397

VL - 58

JO - Water Resources Research

JF - Water Resources Research

IS - 9

M1 - e2022WR032218

ER -