Leaching of Contaminants to Groundwater - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 786

Chapter 18
Leaching of Contaminants to Groundwater

Dirk Mallants, Martinus Th. Van Genuchten, Jirí Šim unek, Diederik Jacques,
and Suresh Seetharam

Abstract In this chapter the water flow and contaminant transport processes in the
unsaturated or vadose zone are described. These processes include water reten-
tion and hydraulic conductivity, evapotranspiration, preferential flow, root water
uptake (water flow) and diffusion, dispersion, advection and volatilization (contam-
inant transport). The equation governing transport of dissolved contaminants in the
vadose zone is obtained by combining the contaminant mass balance with equations
defining the total concentration of the contaminant and the contaminant flux den-
sity. Further attention is this chapter is given to nonequilibrium transport, stochastic
models, multicomponent reactive solute transport, multiphase flow and transport.
Mathematical models should be critical components of any effort to understand
and predict site-specific subsurface water flow and contaminant transport processes.
Generally, models range from relatively simple analytical approaches for analyz-
ing contaminant transport problems during one-dimensional steady-state flow, to
sophisticated numerical models for addressing multi-dimensional variably-saturated
flow and contaminant transport problems at the field scale. An overview is given of
several existing analytical and numerical models. Moreover, several applications to
unsaturated flow and geochemical transport modeling are presented in this chapter.

Contents

18.1 Introduction ........................................... 788

18.2 Variably Saturated Water Flow ...............................

790

18.2.1 Water Retention and Hydraulic Conductivity ..................

791

18.2.2 Mass Balance Equation ............................... 797

18.2.3 Preferential Flow ................................... 799