Quantifying reagent spreading by cross borehole electrical tomography to assess performance of groundwater remediation

This repository contains data related to the articleof the same name, published at Water Resources Research in 2022.

inversion_inputs folder = all cross-borehole ERT/IP data formatted for the software AarhusInv

inversion_results folder = output files from AarhusInv that can be used for plotting and further data analysis, for each inversion

2x32_Z.xml = spread file for the ABEM Terrameter LS2 when two boreholes with 32 electrodes each are connected

hvede_2xbsb.txt = quadrupole series for a given pair of boreholes, including the two single-borehole and two types of cross-borehole configurations. The electrodes order is A-B-M-N. Electrodes 1-32 are in borehole 1, while electrodes 33-64 are in borehole 2.

hvede_2xbsb.xml = protocol file for the ABEM Terrameter LS2, that can be used in combination with the spread file 2x32_Z.xml.

The paper abstract is given below.

In-situ remediation of contaminated groundwater often relies on the installation of a treatment zone 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 treatment zone. 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.