GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 3.2 615 Kotyrba, B. and Schmidt V. [2014] Combination of seismic and resistivity tomography for the detection of abandoned mine workings in Münster/Westfalen, Germany: Improved data interpretation by cluster analysis. Near Surface Geophysics, 2014, 12, 415-425 doi:10.3997/1873-0604.2013056. Meju, M.A., Gallardo, L.A. [2003] Evidence for correlation of electrical resistivity and seismic velocity in heterogeneous near-surface materials. Geophysical research letters, vol. 30, no. 7, 1373. Maraio, S., Bruno, P.P.G. [2015] Near-surface Voids in the Neapolitan Volcanic Tuff [Italy] Detected by Seismic Refraction Tomography. Near Surface Geoscience. EAGE. Turin, Ital, 6 – 10 September 2015. Martorana, R., Capizzi, P., ������������ ��� ����� �� ������ ���������� �� ��������� ���� �� ����� �������������� ��� D’Alessandro A., Luzio D. [2016] ���������� �� ��������� ���� �� ����� �������������� ��� Comparison of different sets of array configurations for multichannel 2DERT acquisition. Journal of Applied Geophysics, 137, 34-48. Riddle, G.I., Hickey, C.J., Schmitt, D.R. [2010] Subsurface tunnel detection using Electrical Resistivity Tomography and Seismic Refraction Tomography: a case study. Keystone, Colorado. SAGEEP 2010. 552-562. Sheehan, J.R., Doll, W.E., Watson, D.B., Mandell, W.A. [2005] Application of Seismic Refraction Tomography to karst cavities. US Geological Survey Karst Interest Group Proceedings, Rapid City,South Dakota, 12–15 September 2005, 29-38. CHERTS FOR MONITORING HYDROCARBON CONTAMINATION L. Capozzoli, V. Giampaolo, E. Rizzo Istituto di Metodologie per le Analisi Ambientali, Consiglio Nazionale delle Ricerche (CNR-IMAA), Tito (PZ), Italy Introduction. ����� ����������� ����� ������� �������� �� ��� �� ��� ���� ��������� Light Non-Aqueous Phase Liquids (LNAPLs) is one of the most dangerous issues for groundwater and sub-surface safety. The contamination due to presence of LNAPLS influences strongly the physical behavior of the soil and understanding how bio-chemical and bio-geophysical properties varies is the crucial key to monitor contamination event. Non- invasive techniques represent a great tool to contribute and support direct measurements, due their high sensibility and low time-consume for spatial and temporal aspects. Anyway a lot of uncertainties are related to the interpretation of non-invasive results mainly due to the heterogeneity characterizing the response observed by the different techniques applied. Indeed the variations of hydrological, physical and bio-chemical properties could be really strong and for this reason the measured results could lead to dangerous misunderstanding overestimating or underestimating the observed phenomenon. At the Hydrogeosite Laboratory of CNR-IMAA a laboratory test was realized and a long- term monitoring was performed to identify the changing response of the groundwater when a LNAPL-contamination was simulated. The monitoring was carried out with use of cross-hole borehole tomographies (CHERTs) to characterize the contamination dynamics after a controlled hydrocarbon spillage occurring in vadose zone. CHERTs are widely used to study and monitor fluid-dynamics and contaminant flow in the subsurface in vadose and saturated zones (Binley et al. , 2002; Cassiani et al. , 2006; Deiana et al. , 2007). The approach with cross borehole resistivity imaging provide a great advantage compared to more conventional surface electrical resistivity tomography, thanks to the obtainable high resolution at high depth (depending on the depth of the well instrumented for the acquisition). Resistivity sections are obtained after inversion of the resistance data adopting finite element methods that allow to compute and show electrical resistivity values which satisfies both the measured dataset and some a priori constraints, in order to stabilize the inversion and constrain the final image (deGroot-Hedlin and Constable, 1990). Laboratory experiments: results and conclusions. A PVC box (53 cm high x 73.5 cm long x 43 cm deep) filled with fine-grained sand was equipped for the experiment as showed in Fig. 1. Moreover, on both sides of the tank a drain has been prepared by using gravel material, in order to simulate a drainage system and to permit a water flow. Two piezometers have been placed in the drain to monitor water level over time (see Fig. 2). The box-sand has been equipped