GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.2 161 formation (mcs) of Monte Cassin [Campanian-Maastrichtian epoch of the Upper cretaceous period, Papani and Zanzucchi (1969)]. There, an experiment of electrical resistivity and time- domain IP tomography was conducted, using a commercial geo-resistivity meter capable of transmitting controlled current intensities, in the range of 1 mA to 1 A (ABEM SAS4000/ ES464, Sweden). To this end, a profile of 72 m long and 3 m electrode spacing was laid out. Along this profile two data subsequent datasets were acquired using the Wenner-Schlumberger electrode array and two current intensities: 50 mA and 500 mA. The 2D inversion sections of both resistivity and chargeability distributions were obtained using the commercial software RES2DINV tm , based on the Gauss-Newton inversion method (Loke and Barker, 1996) (Figs. 2a to 2d). While chargeability strongly decreases with increased current intensity, some increase of resistivity is observed in those more resistive volumes (the red color resistivity body indicated with the letter “R” in Figs. 2a and 2b) that, given the local geology and locations of water collectors, certainly correspond to the sandstone aquifer. The authors are glad to provide a copy of this data set to who is interested. TheTEMexperiment. In the framework of the EUfinanced project “Cities on Power” (www. citiesonpower.eu, report 3.4.5) where a number of TEM measurements were performed at and around the RioloTerme town (Province of Ravenna, Northern Italy). The aim of the survey was to aid in the reconstruction of the subsurface conceptual model for hydrogeological assessment of the test site. In this site, a pilot low-enthalpy geothermal plant was planned to be installed in a 100 m deep borehole. The subsurface geology, as given by the simplified geological map and by the visual inspection of the cutting, consists mainly of clayey layers, with some inclusions of sandstone layers and blocks; the local outcropping formations together with the locations of TEM soundings are shown in Fig. 1b. As can be seen, three soundings (1, 2 and 3) were performed over the FAAts geological formation, composed mainly of fine sandstone and pelitic argillaceous sediments, while the remaining 4, 5 and 6 where located on sediments belonging to the FAA formation: a Blue Clay formation composed of gray argillaceous mudstones with rare and thin sandstone layers. The TEM equipment model GDP-3224 by Zonge Ltd was used for data acquisition. Multi-Function receiver was used to collect the data at the center of a square loop of 50x50 m dimensions. Data were acquired at three different repeating time cycles, at frequencies of respectively 4, 8 and 32 Hz, to get both the maximum resolution in the shallow surface and the maximum investigation depth in accordance with the loop dimensions. Tab. 1 - 1D petrophysical models of soundings 4, 5 and 6. Sounding layer No. ρ Ohmm Thickness m η τ s 4 1 18 13 2.8°-3 0.0125 2 3.5 25 - - 3 0.75 25 - - 4 0.5 45 - - 5 1 18 13 2.7°-3 0.01 2 3.5 25 - - 3 0.75 25 - - 4 0.8 45 - - 6 1 18 13 2.9°-3 0.02 2 1.7 22 - - 3 0.5 35 - - 4 0.7 35 - -