GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 to PWN (a Dutch water management company) facilites in Andijk. Also, to validate data acquired in a new geological setng, a more established geophysical method was used: two underwater ERT profles, 400 m long each, were acquired close to the FloaTEM soundings acquired in the previous days. The North-South profle was acquired with a Wenner array, the East-West was acquired with a Wenner-Schlumberger array. It was used one 400 m long cable with electrode spacing of 5 meters in the central 200 m and 10 meters on the sides, for a total of 61 electrodes. Using this system, it was possible to identfy areas where the contnuity of the clay layer (more conductve) was interrupted and, therefore, it can be seen a freshwater bubble (more resistve) seeping downward from the lake. Conclusions Mapping geological heterogeneites below water bodies is mandatory to study interactons between surface waters and groundwater. The FloaTEM system can be a fast, reliable and efcent soluton for acquiring data above rivers, lakes and other water bodies. This system ofers a good lateral and vertcal resoluton that can help in mapping small-scale heterogeneites, crucial to correctly depict hydrologic frameworks. Furthermore, the FloaTEM results compare well with more established geophysical methods, such as ERT, but can be acquired with a much higher productvity. In this study the FloaTEM mapping was successfully used to identfy interestng underground features in diferent hydrogeological environments, impossible to infer from ground- based data only. References Auken, E., Foged, N., Larsen, J., Lassen, K., Maurya, P., Dath, S., and Eiskjær, T.: tTEM – A towed transient electromagnetc system for detailed 3D imaging of the top 70 m of the subsurface, Geophysics, E13–E22, htps://doi.org/10.1190/geo2018-0355.1 , 2018. Christansen, A. V., Auken, E., and Sørensen, K. I.: The transient electromagnetc method, in: Groundwater Geophysics. A tool for hydrogeology, 1st Edn., edited by: Kirsch, R., Springer, 179– 224, htps://doi.org/10.1007/3-540-29387-6_6, 2006. Danielsen, J. E., Auken, E., Jørgensen, F., Søndergaard, V., and Sørensen, K. I.: The applicaton of the transient electromagnetc method in hydrogeophysical surveys, J. Appl. Geophys., 53, 181–198, 2003.  Fiandaca, G., Zhang, B., Chen, J., Signora, A., Daut, F., Galli, S., Sullivan, N.A.L., Bollino, A., Viezzoli, A. (2024). EEMverter, a new 1D/2D/3D inversion tool for Electric and Electromagnetc data with focus on Induced Polarizaton. GNGTS 2024, 13-16 February 2024, Ferrara, Italy. Fiterman, D. V. and Deszcz-Pan, M.: Helicopter EM mapping of saltwater intrusion in Everglades Natonal Park, Florida, Explor. Geophys., 29, 240–243, htps://doi.org/10.1071/EG998240 , 1998.