Fresh water is an essential element of life, the main source of drinking water being represented by groundwater. Since aquifers provide drinking water needs of humanity, water quality and pollutant transport to the saturated zone has to be carefully monitored. Unsaturated zone acts as a buffer between surface waters and aquifers.
Environmental protection in general and especially that of the groundwater is a current issue and a priority for the international community and for Romania as part of the European Union. The European Union adopted in 2000 the Water Framework Directive (WFD), which sets 2015 as the deadline for achieving good quality for all European waters and intends to ensure sustainable water use throughout Europe. Groundwater management is both quantitatively aiming to avoid overexploitation and in terms of quality, aiming at limiting pollution of aquifer layers and this is a priority for Romania.
The overall aim of the thesis was a study comprehensive and complex of modeling flow and transport of pollutants in porous media.
Problems to be solved have followed scientific objectives: modeling coupled flow and transport in porous media saturated and unsaturated, infiltration model study with numerical applications made through own programs, comparative study of two methods for estimating groundwater recharge, global and local optimization techniques in parameter estimation problems or groundwater remediation as well as establishing sanitary protection zones and a hydrogeological protection perimeter.
I thought it is appropriate to address these issues to have a unified vision of the processes occurring in porous media. The proposed theme contains on the one hand a number of topics dedicated to theoretical approaches concerning coupled modeling of physical processes of flow and transport in the saturated and unsaturated areas, as well as modern numerical techniques for solving mathematical and numerical, effectively, a wide variety of problems.
1.2. Scientific and technical presentation of the thesis
The thesis is divided into eight chapters.
The first chapter “Introduction” provides an overview of the topics addressed, which consists in modeling coupled flow and transport, as well as the use of local and global optimization methods for solving inverse problem in hydrogeology.
The second chapter “Mathematical modeling of flow in porous media” treats the matter of flow in the unsaturated and saturated media. The numerical application makes a comparative estimate of wetting front based on Richards equation and Green-Ampt model.
The third chapter “Mathematical modeling of pollutant transport in porous media” refers to the phenomenon of pollution in the unsaturated zone and the saturated. Groundwater and soil pollution is a complex phenomenon that depends on the nature of the porous medium and the nature of the pollutants.
Chapter four deals with “Numerical modeling of flow and transport in porous media by finite difference method”. It presents multiple meshing scheme advantages and disadvantages in flow and transport numerical model as well as numerical methods for solving linear systems arising from the mesh.
Chapter five, entitled “Local and global optimization methods in hydrogeology” is addressing both gradient methods, Newton and Levenberg-Marquand method (GLM) to estimate hydrogeological parameters involved in the flow and transport, as well as metaheuristics methods applied for groundwater remediation processes. As a numerical application, I use genetic algorithms module Modular Groundwater Optimizer (MGO) to optimize flow and / or locations of a set of drills to ensure isolation of contaminated areas.
Chapter six, “Calculation software” presents modules used in making applications and case studies. The aim is a comparative study of the various programs the flow and transport modeling: Groundwater Modeling System (GMS), Groundwater Vistas (GV) containing modules: MODFLOW, MT3DMS, PEST and MGO.