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In many parts of the world, groundwater resources are under increasing threat from growing demands, wasteful use, and contamination. To face the challenge, good planning and management practices are needed. A key to the management of groundwater is the ability to model the movement of fluids and contaminants in the subsurface. The purpose of this book is to construct conceptual and mathematical models that can provide the information required for making decisions associated with the management of groundwater resources, and the remediation of contaminated aquifers.

The basic approach of this book is to accurately describe the underlying physics of groundwater flow and solute transport in heterogeneous porous media, starting at the microscopic level, and to rigorously derive their mathematical representation at the macroscopic levels. The well-posed, macroscopic mathematical models are formulated for saturated, single phase flow, as well as for unsaturated and multiphase flow, and for the transport of single and multiple chemical species. Numerical models are presented and computer codes are reviewed, as tools for solving the models. The problem of seawater intrusion into coastal aquifers is examined and modeled. The issues of uncertainty in model input data and output are addressed. The book concludes with a chapter on the management of groundwater resources. Although one of the main objectives of this book is to construct mathematical models, the amount of mathematics required is kept minimal.

Modeling Groundwater Flow and Contaminant Transport

PrefaceList of Main Symbols1 INTRODUCTION1.1 Role of Groundwater in Water ResourcesSystems1.1.1 The hydrological cycle1.1.2 Surface water versus groundwater1.1.3 Characteristics of groundwater1.1.4 Functions of aquifers1.1.5 Subsurface contamination1.1.6 Sustainable yield1.2 Modeling1.2.1 Modeling concepts1.2.2 Modeling process1.2.3. Model use1.3 Continuum Approach to Transport in Porous Media1.3.1 Phases, chemical species and components1.3.2 Need for a continuum approach1.3.3 Representative elementary volume and averages1.3.4 Scale of heterogeneity in continuum models1.3.5 Homogenization1.4 Scope and Organization2 GROUNDWATER AND AQUIFERS2.1 Definitions of Aquifers2.2 Moisture Distribution in a Vertical Soil Profile2.3 Classification of Aquifers2.4 Solid Matrix Properties2.4.1 Soil classification based on grain size distribution2.4.2 Porosity and void ratio2.4.3 Specific surface2.5 Inhomogeneity and Anisotropy2.6 Hydraulic Approach to Flow in Aquifers3 REGIONAL GROUNDWATER BALANCE3.1 Groundwater Flow and Leakage3.1.1 Inflow and outflow through aquifer boundaries3.1.2 Leakage3.2 Natural Replenishment from Precipitation3.3 Return Flow from Irrigation and Sewage3.4 Artificial Recharge3.4.1 Objectives3.4.2 Methods3.5 River-Aquifer Interrelationships3.6 Springs3.7 Evapotranspiration3.8 Pumping and Drainage3.9 Change in Storage3.10 Regional Groundwater Balance4 GROUNDWATER MOTION4.1 Darcy's Law4.1.1 The empirical law4.1.2 Extension to a three-dimensional space4.1.3 Hydraulic conductivity4.1.4 Extension to anisotropic porous media4.2 Darcy's Law as Momentum Balance Equation4.2.1 Darcy's law by volume averaging4.2.2 Darcy's law by homogenization4.2.3 Effective hydraulic conductivity by homogenization4.3 Non-Darcy Laws4.3.1 Range of validity of Darcy's law4.3.2 Non-Darcian motion equations4.4 Aquifer Transmissivity4.5 Dupuit Assumption for a Phreatic Aquifer5 WATER BALANCES AND COMPLETE FLOW MODEL5.1 Mass Balance Equations5.1.1 Fundamental mass balance equation5.1.2 Deformable porous medium5.1.3 Specific storativity5.1.4 Flow equations5.2 Initial and Boundary Conditions5.2.1 Boundary surface5.2.2 Initial and general boundary conditions5.2.3 Particular boundary conditions5.3 Complete 3-D Mathematical Flow Model5.3.1 Well-posed problem5.3.2 Conceptual model5.3.3 Standard content of a flow model5.4 Modeling 2-D Flow in Aquifers5.4.1 Deriving the 2-D balance equations by integration5.4.2 Another derivation of the 2-D balance equations5.4.3 Complete aquifer flow models5.4.4 Effect of storage changes in an aquitard5.4.5 Multilayered aquifer-aquitard system5.4.6 Groundwater maps and streamlines5.5 Land Subsidence5.5.1 Integrated water mass balance equation5.5.2 Integrated equilibrium equation5.5.3 Terzaghi-Jacob vs. Biot approaches5.5.4 Land subsidence produced by pumping6 MODELING FLOW IN THE UNSATURATED ZONE6.1 Statics of Fluids in the Unsaturated Zone6.1.1 Water content6.1.2 Surface tension6.1.3 Capillary pressure6.1.4 Retention curve6.1.5 Experimental determination of