This dataset contains the cross-borehole ERT/IP data and inversion results used in the article whose title is given above, currently in revision at Water Resources Research. The paper abstract is given below. Data is formatted to work with the software AarhusInv, and results are output files from AarhusInv that can be used for plotting and further data analysis. 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 and compares well with estimations by grain size analyses from the treatment zone. However, the IP-based K-field fails at predicting injection paths, suggesting and the creation of engineered 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.