256
8. Applications of Groundwater Quality Models
ative term in Eq. (8.1.8), the equation can be turned into a system of linear
algebraic equations:
([F] + L[G]) {C}k+l = ~t[G]{Ch - {H}. (8.1.11)
All coefficients depending on ljJ in the above equation are expressed by
{1jJ h+1/2' which is a mean of the values {1jJ hand {1jJ h+1' Based on the known
{Ch, we can solve Eq. (8.1.11) to obtain the concentration distribution at the
next time step {C}k+l' thereby complete the calculation of one time step.
Numerical simulation is a powerful tool for understanding and analyzing
solute transport in the unsaturated zone. In practical applications, it is very
difficult to obtain reliable input parameters because it requires experimental
studies and theoretical analyses both in the field and in the laboratory. Xiao
(1984) presented some theoretical results for solute transport in the unsaturated zone. In a saturated-unsaturated model presented by Yang (1988), the
immobile water phase was considered. The inverse problem of groundwater
flow and mass transport in the unsaturated zone was considered by Kool et
al. (1987), Kool and Parker (1988), and Mishra and Parker (1989).
Groundwater flow in the unsaturated zone can be seen as a special case of
two-phase j70w (Bear, 1979). The governing equations consist of mass balance
equations for both air and water phases. In recent years, more complicated
cases, including various multicomponent transport in multiphase flow, were
considered. For ex am pIe, Falta et al. (1992) presented a multidimensional
integral finite difference method for modeling the steam displacement of
non-aqueous phase liquid (NAPL) contaminants in shallow subsurface
systems, where three flowing phases (gas, aqueous, and NAPL) and three
mass components (air, water and an organic chemical) are considered. In
this model, the effects of adsorption and heat transport are also included.
8.1.4 Groundwater Pollution of Fractured Aquifers
The problem of solute transport in Jractured aquifers is currently a hot
subject. It is interesting in theoretical study and important in practical
application.
Because of the existence of fractures, the solute distribution depends on
both the microstructure and the macrostructure of the fractures in a large
degree. Generally speaking, along fractures the solute moves faster and
pro pagates farther than it does in a loose rock formation. Figure 8.1 shows
the process of solute transport in a fractured aquifer. In the fractures, the
solute transport is controlled by both advection and dispersion, and is often
domina ted by advection. It should not be ignored that porous blocks among
the fractures can store the solute. In the porous blocks, the flow velocity is
very small, so the solute transport is usually dominated by dispersion and
molecular diffusion.
8. Applications of Groundwater Quality Models
ative term in Eq. (8.1.8), the equation can be turned into a system of linear
algebraic equations:
([F] + L[G]) {C}k+l = ~t[G]{Ch - {H}. (8.1.11)
All coefficients depending on ljJ in the above equation are expressed by
{1jJ h+1/2' which is a mean of the values {1jJ hand {1jJ h+1' Based on the known
{Ch, we can solve Eq. (8.1.11) to obtain the concentration distribution at the
next time step {C}k+l' thereby complete the calculation of one time step.
Numerical simulation is a powerful tool for understanding and analyzing
solute transport in the unsaturated zone. In practical applications, it is very
difficult to obtain reliable input parameters because it requires experimental
studies and theoretical analyses both in the field and in the laboratory. Xiao
(1984) presented some theoretical results for solute transport in the unsaturated zone. In a saturated-unsaturated model presented by Yang (1988), the
immobile water phase was considered. The inverse problem of groundwater
flow and mass transport in the unsaturated zone was considered by Kool et
al. (1987), Kool and Parker (1988), and Mishra and Parker (1989).
Groundwater flow in the unsaturated zone can be seen as a special case of
two-phase j70w (Bear, 1979). The governing equations consist of mass balance
equations for both air and water phases. In recent years, more complicated
cases, including various multicomponent transport in multiphase flow, were
considered. For ex am pIe, Falta et al. (1992) presented a multidimensional
integral finite difference method for modeling the steam displacement of
non-aqueous phase liquid (NAPL) contaminants in shallow subsurface
systems, where three flowing phases (gas, aqueous, and NAPL) and three
mass components (air, water and an organic chemical) are considered. In
this model, the effects of adsorption and heat transport are also included.
8.1.4 Groundwater Pollution of Fractured Aquifers
The problem of solute transport in Jractured aquifers is currently a hot
subject. It is interesting in theoretical study and important in practical
application.
Because of the existence of fractures, the solute distribution depends on
both the microstructure and the macrostructure of the fractures in a large
degree. Generally speaking, along fractures the solute moves faster and
pro pagates farther than it does in a loose rock formation. Figure 8.1 shows
the process of solute transport in a fractured aquifer. In the fractures, the
solute transport is controlled by both advection and dispersion, and is often
domina ted by advection. It should not be ignored that porous blocks among
the fractures can store the solute. In the porous blocks, the flow velocity is
very small, so the solute transport is usually dominated by dispersion and
molecular diffusion.