Karstic and fractured aquifers are among the most important drinking water resources. At the same time, they are particularly vulnerable to contamination. A detailed scientific knowledge of the behavior of these aquifers is essential for the development of sustainable groundwater management concepts. Due to their special characteristics (extreme anisotropy and heterogeneity), research aimed at a better understanding of flow, solute transport and biological processes in these hydrogeology systems is a very important scientific challenge. This study aims to quantify the vertical leakage in karstic and fractured limestone that overlays the deep aquifer of Alta Murgia. This area, close to Altamura, has been affected by sludge waste deposits derived from municipal and industrial wastewater treatment plants. These waste disposal have caused soil-subsoil contamination with toxics such as hydrocarbons, perchlorethlyne, heavy metals, etc. Knowledge of the flow rate of the unsaturated zone percolation is needed to investigate the vertical migration of pollutants and the vulnerability of the deep aquifer. At the Altamura site infiltrometer flow measurements, more commonly utilized for unconsolidated granular porous media, were conducted in order to calibrate a model of vertical flow in unsaturated subsoil made of a layer of about 20 cm thick of "terra rossa", a nonconsolidated soil, relatively impermeable which overlay fractured limestone and often fill the fractures partially. The estimation of vertical flow into the fractures was supported also by the flow rate determination carried out on measurements of subsoil electric resistivity. The latter were obtained analyzing Electric Resistivity Images made during the infiltration test. Vertical movement of water in a fracture plane under unsaturated conditions has been investigated by means of a numerical model. Different portions of the fracture were occupied by wetting and non-wetting phases according to capillary pressure and global accessibility criteria. The finite difference method was used to solve the flow equations. An internal iteration method was used at every time step to evaluate the nodal value of the pressure head, in agreement with the mass-balance equation and the characteristic functional relationships of the coefficients. The variable apertures were calculated by means of a spatial correlation matrix which was considered anisotropic in the fracture plane.
EVALUATION OF VERTICAL FLOW IN FRACTURED AND KARSTIC SUBSOIL OF ALTAMURA (SOUTHERN ITALY) USING FIELD INFILTROMETER MEASUREMENTS
CAPUTO MC;DE CARLO L;MASCIOPINTO C;
2007
Abstract
Karstic and fractured aquifers are among the most important drinking water resources. At the same time, they are particularly vulnerable to contamination. A detailed scientific knowledge of the behavior of these aquifers is essential for the development of sustainable groundwater management concepts. Due to their special characteristics (extreme anisotropy and heterogeneity), research aimed at a better understanding of flow, solute transport and biological processes in these hydrogeology systems is a very important scientific challenge. This study aims to quantify the vertical leakage in karstic and fractured limestone that overlays the deep aquifer of Alta Murgia. This area, close to Altamura, has been affected by sludge waste deposits derived from municipal and industrial wastewater treatment plants. These waste disposal have caused soil-subsoil contamination with toxics such as hydrocarbons, perchlorethlyne, heavy metals, etc. Knowledge of the flow rate of the unsaturated zone percolation is needed to investigate the vertical migration of pollutants and the vulnerability of the deep aquifer. At the Altamura site infiltrometer flow measurements, more commonly utilized for unconsolidated granular porous media, were conducted in order to calibrate a model of vertical flow in unsaturated subsoil made of a layer of about 20 cm thick of "terra rossa", a nonconsolidated soil, relatively impermeable which overlay fractured limestone and often fill the fractures partially. The estimation of vertical flow into the fractures was supported also by the flow rate determination carried out on measurements of subsoil electric resistivity. The latter were obtained analyzing Electric Resistivity Images made during the infiltration test. Vertical movement of water in a fracture plane under unsaturated conditions has been investigated by means of a numerical model. Different portions of the fracture were occupied by wetting and non-wetting phases according to capillary pressure and global accessibility criteria. The finite difference method was used to solve the flow equations. An internal iteration method was used at every time step to evaluate the nodal value of the pressure head, in agreement with the mass-balance equation and the characteristic functional relationships of the coefficients. The variable apertures were calculated by means of a spatial correlation matrix which was considered anisotropic in the fracture plane.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
