Modeling Unsaturated-Saturated Flow and Nickel Transport in Fractured Rocks

This study investigated the modeling of variably saturated flow and Ni transport in frac- tured rocks at a site (Altamura, southern Italy) polluted in 2001 by unauthorized sludge waste disposal. Time-lapse electrical resistivity tomography (ERT) and infiltrometer experi- mental results were used to constrain near-surface boundary conditions in an unsaturated flow model. A plastic ring was used as an infiltrometer because its experimental setup is very versatile and adaptable to many different geological conditions, taking into con- sideration irregularities in the soil and rock surfaces. The proposed methodology allows switching from the tomography to the map of water pressure contour lines obtained by the model by making the time-lapse ERT an effective tool to reduce computational uncertain- ties. Simulation results predicted both the concentration and the residence time of the Ni in the vadose zone of the Altamura site. These results were used to successively investigate the horizontal Ni transport into the deep fractured aquifer. Simulations provided apparent Ni pathways in the groundwater and expected concentrations in a downstream well, placed 10.9 km from the contamination sources. The agreement of the results with the sampling data collected has confirmed that the groundwater was polluted for 16 mo by Ni. The con- tamination plume started during the winter of 2004 and moved in the groundwater toward the sea at an average velocity of 10 m/d.