Geophysical electrical resistivity tomography (ERT) is a promising measurement technique for non-intrusive monitoring of an engineered barrier system (EBS) during the operational phase of geological disposal of high-level radioactive waste. Electrical resistivity is sensitive to water content and temperature, which are the key variables characterizing the response of the EBS. In order to assess the technology readiness level of the ERT technique for EBS operational monitoring, a field demonstrator has been developed at the underground research laboratory (URL) in Tournemire (France) within the project ‘Modern 2020’. Preliminary ERT surveys were carried out in January and November 2017 to establish the background resistivity of the experimental area and assess the quality of electrode installation and survey protocols. Results of the surveys confirmed that the resistivity of the host rock in the demonstrator area is quite homogenous and lower than 100 Ωm in accordance with independent measurements carried out in previous campaigns. In addition, the lesson learned from the blank tests allowed identifying key requirements for effective ERT measurements. These include the need for a 3D electrode configuration, bespoke measurement protocols designed on the basis of the sensitivity analysis of the geometric factor and the collection of reciprocal data for enhanced data quality control.