Concetta I. Giasi

Fluid flow modeling of a coastal fractured karstic aquifer by means of a lumped parameter approach

Fluid flow and solute transport phenomena in fractured and karstic aquifers remain an open issue that calls the attention of numerous researchers belonging to different disciplinary fields as far as the aspects linked both to shallow and to deep phenomena are concerned. The hydrogeologic knowledge of these phenomena proves to be of high importance especially if considered in relationship with water resource exploitation, with the problems linked to contamination and the ones linked to urban and industrial development of the territory. In the examined area, characterized by a dismissed contaminated site, the realization of the landfill has required the development of a 3D flow model supported by a detailed local scale geologic model in order to evaluate the effects on groundwater flow and subsequently on contaminant propagation. The results of the flow model prove to be coherent with the fractured and karstic nature of the site in that they show at higher depths the presence of a subterranean stream channel that would speed up pollutant propagation. The obtained results represent the fundamental basis to implement a transport model that will permit to achieve a more in depth knowledge of the subsoil transport phenomena, and therefore to optimize any anthropic intervention that can involve the site.

Application of modeling for optimal localization of environmental monitoring sensors

The control of environmental phenomena is based on the existence of quantifiable and measurable parameters representative of the phenomena themselves. In the case of studies concerning contaminated aquifers, after an initial step of characterization it is necessary to implement groundwater hydrogeochemical monitoring phases.

Kinematic diffusion approach to describe recharge phenomena in unsaturated fractured chalk

Abstract When dealing with groundwater resources, a better knowledge of the hydrological processes governing flow in the unsaturated zone would improve the assessment of the natural aquifer recharge and its vulnerability to contamination. In North West Europe groundwater from unconfined chalk aquifers constitutes a major water resource, therefore the need for a good hydrological understanding of the chalk unsaturated zone is essential, as it is the main control for aquifer recharge. In the North Paris Basin, much of the recharge must pass through a regional chalk bed that is composed of a porous matrix with embedded fractures. The case study regards the role of the thick unsaturated zone of the Cretaceous chalk aquifer in Picardy (North of France) that controls the hydraulic response to rainfall. In order to describe the flow rate that reaches the water table, the kinematic diffusion theory has been applied that treats the unsaturated water flow equation as a wave equation composed of diffusive and gravitational components. The kinematic diffusion model has proved to be a convenient method to study groundwater recharge processes in that it was able to provide a satisfactory fitting both for rising and falling periods of water table fluctuation. It has also proved to give an answer to the question whether unsaturated flow can be described using the theory of kinematic waves. The answer to the question depends principally on the status of soil moisture. For higher values of hydraulic Peclet number (increasing saturation), the pressure wave velocities dominate and the preferential flow paths is provided by the shallow fractures in the vadose zone. With decreasing values of hydraulic Peclet number (increasing water tension), rapid wave velocities are mostly due to the diffusion of the flow wave. Diffusive phenomena are provided by matrix and fracture-matrix interaction. The use of a kinematic wave in this context constitutes a good simplified approach especially in cases when there is a lack of information concerning the hydraulic properties of the fractures/macropores close to saturation.

Design of optic sensor for hydrocarbon detection

A computer code for the design of optical sensors is developed, the electromagnetic model taking into account both lossy guided and leaky modes. For a concentration C = 700 ppm of toluene in water, the maximum absorbance of a sensor having length L=2 cm is A ≡ 10 for the guided quasi-TM00 mode, while that pertaining to the leaky quasi-TM12 mode is A ≈ 1200. The simulation results indicate that a selective excitation of the suitable propagation modes could enhance the sensor performance.