be integrated into risk assessment of contaminated sites, optimal selection of new
sites, and determination of design parameters. The application in groundwater
pollution risk assessment requires the support of mathematical models and simulation models. Using established mathematical formula, parameters are quantified to
obtain the comprehensive index of regional groundwater pollution risk.
In essence, process simulation is a part of the numerical simulation of groundwater. MODFLOW is an early groundwater simulation software developed by the
US Geological Survey (USGS), which is mainly applied to the numerical simulation of three-dimensional finite-difference groundwater flow in porous media.
Afterwards, many software and models for groundwater numerical simulation
emerged, such as FEFLOW, HYDRUS, GMS, Groundwater Vistas, Visual
Modflow, and Geostudio. Among them, FEFLOW and MT3DMS (groundwater
solute transport model) have been recognized as standard models for groundwater
flow and pollutant migration.
The application of mathematical models and simulation models facilitates
quantitative and systematic assessment and more real results about groundwater
pollution risk. However, great uncertainties lie in the internal and external characteristics and the formation mechanism of complex, dynamic and open groundwater system. It is also difficult to obtain hydrogeological data and physical
parameters on which the simulation relies. Due to the limitations of human cognition and the temporal and spatial constraints of monitoring activities, the simulation is too ambiguous to reflect, in many cases, the true level of risk. In addition,
the process simulation method is not combined with the disaster theory, but rather
focuses on the temporal and spatial distribution characteristics of pollutants, which
hinders the representation of the true connotation of risk.
4.2.5.3 Uncertainty Analysis Method
The essence of risk assessment is uncertainty analysis because without uncertainty,
there is no risk. The results will be more scientific if the level of risk is reflected
based on qualitative and quantitative research of uncertain factors in the whole
process. The groundwater system, huge, dynamic and open as it is, has complex
internal and external structures and strong uncertainties. With the establishment and
development of uncertainty theory, the related theories have been gradually introduced into groundwater pollution risk assessment. The main approaches for
uncertainty analysis in this field can be classified into three categories: stochastic
model based on probability theory, fuzzy mathematics based on fuzzy set theory,
and coupled stochastic-fuzzy analysis.
The existing relevant studies mainly focus on groundwater health risk assessment because of simple models and fewer parameters. In contrast, groundwater
pollution risk assessment needs to consider complex problems and various
parameters, so under uncertain conditions, emphasis is put on intrinsic
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4 Risk Assessment of Groundwater Contamination Sites
sites, and determination of design parameters. The application in groundwater
pollution risk assessment requires the support of mathematical models and simulation models. Using established mathematical formula, parameters are quantified to
obtain the comprehensive index of regional groundwater pollution risk.
In essence, process simulation is a part of the numerical simulation of groundwater. MODFLOW is an early groundwater simulation software developed by the
US Geological Survey (USGS), which is mainly applied to the numerical simulation of three-dimensional finite-difference groundwater flow in porous media.
Afterwards, many software and models for groundwater numerical simulation
emerged, such as FEFLOW, HYDRUS, GMS, Groundwater Vistas, Visual
Modflow, and Geostudio. Among them, FEFLOW and MT3DMS (groundwater
solute transport model) have been recognized as standard models for groundwater
flow and pollutant migration.
The application of mathematical models and simulation models facilitates
quantitative and systematic assessment and more real results about groundwater
pollution risk. However, great uncertainties lie in the internal and external characteristics and the formation mechanism of complex, dynamic and open groundwater system. It is also difficult to obtain hydrogeological data and physical
parameters on which the simulation relies. Due to the limitations of human cognition and the temporal and spatial constraints of monitoring activities, the simulation is too ambiguous to reflect, in many cases, the true level of risk. In addition,
the process simulation method is not combined with the disaster theory, but rather
focuses on the temporal and spatial distribution characteristics of pollutants, which
hinders the representation of the true connotation of risk.
4.2.5.3 Uncertainty Analysis Method
The essence of risk assessment is uncertainty analysis because without uncertainty,
there is no risk. The results will be more scientific if the level of risk is reflected
based on qualitative and quantitative research of uncertain factors in the whole
process. The groundwater system, huge, dynamic and open as it is, has complex
internal and external structures and strong uncertainties. With the establishment and
development of uncertainty theory, the related theories have been gradually introduced into groundwater pollution risk assessment. The main approaches for
uncertainty analysis in this field can be classified into three categories: stochastic
model based on probability theory, fuzzy mathematics based on fuzzy set theory,
and coupled stochastic-fuzzy analysis.
The existing relevant studies mainly focus on groundwater health risk assessment because of simple models and fewer parameters. In contrast, groundwater
pollution risk assessment needs to consider complex problems and various
parameters, so under uncertain conditions, emphasis is put on intrinsic
88
4 Risk Assessment of Groundwater Contamination Sites