A geophysical survey including electromagnetic induction (EMI) and electrical resistivity tomography (ERT) methods was applied and assessed with a 40‐trench sampling grid to delineate the geometry of an urban fill layer. Classical investigation techniques, such as excavation, offer localized information and suffer from time and budget constraints for environmental assessments. Near‐surface geophysics can provide the required spatial sampling to evaluate the coverage of anthropogenic soils in a time‐effective and quasi‐continuous manner. Fast‐acquisition and high‐spatial‐coverage EMI mapping and high‐vertical‐resolution ERT were implemented to delineate a suspicious urban fill on a 5‐ha site in a suburban region, which will host the buildings of a commercial complex. The ERT data and 40 trench excavations revealed an urban fill thickness ranging from 0.4 to 3.6 m overlying a calcareous substratum. After ERT–EMI calibration, a two‐layer model was introduced into the one‐dimensional (1‐D) inversion of the EMI data for estimating the geometry of the urban fill layer across the study site. The EMI 1‐D inversion results indicated that the predicted urban fill thicknesses were consistent with 70% of the measured values (27 out of 40 excavation sites). Resistive ground, large 3‐D structures and the heterogeneity of urban fill affected the EMI and ERT measurements and increased the difficulty of estimating its spatial distribution. In this paper, we present a measurement protocol that can guide land‐use development and be reproduced to investigate brownfield sites. Highlights Urban soils are poorly characterized by localized investigations for environmental assessments. Spatial EMI data from an urban fill context were calibrated by ERT for thickness inversion. The ERT–EMI inversion reconstructed the urban fill thickness for 70% of the excavation points. Geophysical techniques can reduce uncertainties for site rehabilitation and land‐use development.

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The frequency-domain electromagnetic induction method is a very efficient and convenient method to investigate a site of interest and for a large range of applications including hydrogeology and archaeology. Besides an easy infield acquisition, the data can be used to estimate the electrical, magnetic and, in certain cases, dielectric properties of the ground. It does, however, require calibration to get reliable quantitative values of these properties. We propose here an original and reliable self-calibration method, specific to multi-frequency measurements in the range of (5-100 kHz)-based only on the consistency between the data at different acquisition frequencies. Contrary to other existing cross-calibration procedures, no additional measurements with other methods are necessary. This self-calibration (quadrature and in-phase components of the electromagnetic induction signal) procedure is tested at a test site located at the centre for studies on risks, the environment, mobility and urban planning Normandie-Centre facilities (Rouen, France). The developed quadrature self-calibration has been successfully compared with the usual electrical resistivity tomography -electromagnetic induction cross-calibration procedure. The main results reveal the potential of systematic assessment of all electromagnetic parameters from multi-frequency and multi-configuration electromagnetic induction data: The electrical resistivity and the magnetic susceptibility are estimated from the low-frequency range, whereas the highest part of the frequency range is used for the dielectric permittivity.