The characterisation of aquifers by means of resistivity investigations

The present paper contains the description of data collection and the main results that were achieved in the frame of the CAMI project using resistivity-based methods. In particular the Electrical Resistivity Tomography (ERT) was used to get detailed 2D and 3D resistivity models of the shallowest part of the subsurface in the test area (down to some decades of metres), while to reach the whole designed investigation depth Magnetotellurics (MT) and “Time-Domain ElectroMagnetic method” (TDEM) were used and their costs-to benefits ratios were evaluated. As far as the results of the resistivity investigation are concerned, a reliable 4D model of the resistivity distribution down to more than 500 m b.g.l. was obtained by TDEM data inversion. This model showed variations of the resistivity vs time of the first confined aquifer which were in excellent agreement with direct data. A reliable estimation of the effective porosity was also obtained for the same aquifer. Finally an important fresh water aquifer was found at depth, which was then reached and characterised by a purposely drilled hole.