A Geostatistical Simulation Approach to a Pollution Case in Northeastern Italy
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A Geostatistical Simulation Approach to a Pollution Case in Northeastern Italy1 Paolo Fabbri2 and Sebastiano Trevisani2 The study zone is located in the city of Padova (the Veneto region, NE Italy). The industrial activities present in this area since 1950 have produced very high concentrations of Pb, Zn, Cu, Pcb and oils until a depth of 7 m. The unsaturated and the saturated zones are both polluted. Because of the abundance of Pb values it was decided to analyze the lead distribution in the studied zone. In many studies of the polluted sites, the geometry of the investigated volume is highly anisotropic. Generally we have an extension of some hectares in the horizontal plane and of a few meters in depth. It is likely that different horizontal spatial continuity structures in pollution distribution are found at different depths both for the layered nature of the medium and for the transition between unsaturated and saturated conditions. In such conditions the decision to divide a 3D problem into 1D and 2D problems can be useful. Initially the studied volume was divided into seven layers up to 5 m in depth; the study was then approached in two phases. First, the Pb values in the vertical direction were analyzed, considering a derive along z, and estimating the values using the Kriging with Trend (KT) method. Thus it was possible to increase the data in the z direction, especially in the deeper layers. Second, 500 realizations of the Pb distribution for each of the seven layers were simulated using the simulated annealing procedure. Finally, results were presented and discussed for each layer in terms of median and probability maps. KEY WORDS: variographic analysis; Kriging with trend; simulated annealing.
INTRODUCTION The studied area (4–5 ha) is located in the city of Padova in the Veneto region of NE Italy (Fig. 1). The pollution found is principally related to the demolition of cars and the storage of exhausted lubricating oils. This industrial activity was present in the studied area from 1950 until 1997. The complexity of the pollution phenomena and the hydrogeological variability require adequate mathematical tools in order to approach a problem like this. The aim of this paper is to study a typical 3D contamination problem in an urban area approaching it as different 2D problems, using geostatistical estimation and simulation tools together. 1Received
26 November 2002; accepted 6 December 2004.
2Dipartimento di Geologia, Paleontologia e Geofisica, Universit` a degli Studi di Padova, 35127 Padova,
Italy; e-mail: [email protected]. 569 C 2005 International Association for Mathematical Geology 0882-8121/05/0800-0569/1
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Fabbri and Trevisani
Figure 1. Location of the studied area and its geological cross-section.
The pollution at the site is characterized by the presence of heavy metals (Pb, Zn, Cu), Pcb and oils. Peak concentrations found were 9500 ppm lead, 8700 ppm zinc and 30,235 ppm oil. Some of the pollution sources are known and visible; in fact some open concrete tanks containing
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