Modelling Unsaturated Flow and Transport of Pollutant in a Fractured Limestone Affected by Industrial Sludge Deposits at the Altamura Site (South Italy)

Karstic and fractured aquifers are among the most important reservoirs for drinking and irrigation water. At the same time, they are particularly vulnerable to contamination. A detailed knowledge of the behavior of pathways of pollutants which affect these aquifers is essential for both groundwater protection and management. Due to extreme anisotropy and heterogeneity, research aimed at a better understanding of flow, solute transport and biological processes in these hydrogeology systems is a difficult scientific challenge.

This study presents an integration of an electrical-resistivity technique with large ring infiltrometer tests in order to calibrate a mathematical model able to quantify the vertical unsaturated flow and pollutant transport in vertical fracture planes. These methods, which are widely used in soils, are not yet applied on the rock outcrops in extensive way and some adaptations are necessaries in order to have an easy ring installation without appreciable lateral leakages. The experimental test measured the quasi-steady unsaturated flow in vertical fractures and, simultaneously, the change with depth of rock-water electrical resistivity vs. time.

The studied fractured limestone outcrop overlies the deep groundwater of the Murgia (South Italy), which supplies drinking and irrigation water in the Apulia region. The field test was performed in a 200-Ha area that has been intensively utilized for grain corn production, which has been recently (2001) subjected to unauthorized industrial sludge deposits. The latter have caused soil and subsoil contamination by toxics such as heavy metals (nickel, chrome, zinc, iron, etc.), arsenic, hydrocarbons, ammonium and nitrites. The vertical movement of water and pollutants in fractures was simulated by considering wetting and non-wetting phases according to the capillary pressure and global accessibility criteria in fractures with variable apertures. The finite difference method was used to solve the flow and convection-dispersion equations of toxics in fractures, under unsaturated conditions.