Environmental Engineering Reference
In-Depth Information
The factors and elements to be considered fall conveniently into two groups: (1) trans-
port and (2) reactions. Two types of analytical-computer models have been developed:
(1) models dealing with fate and transport of contaminants and (2) models that take into
account geochemical reactions and their products. By and large, most of the models deal-
ing with fate and transport of contaminants are nonreactive models. This means to say
that other than using the partitioning coeficients to account for sorption of contaminants
from the porewater, no attempt is made to account for the chemical reactions in the soil-
water system or that all reactions are immediate. In particular, speciation and complex-
ations are not included in the structuring of the basic functions. Attempts have been made
(and are being made) to develop reactive fate and transport models. In the second type of
models, we have geochemical models that pay attention to geochemical speciation equi-
libria between the various phases (solids, liquid, and gaseous) in the subsurface setting.
These include the dissolved and adsorbed elements in the various phases.
Assessment and prediction of the transport and fate of contaminants commonly rely
on analytical and/or numerical (computer) models designed to take into account the vari-
ous processes, site contamination situations, and properties of the contaminants and sub-
surface materials. These models are useful for regulatory agencies in risk management
and performance assessment of target sites and situations, for operators of landills, and
for those involved in site remediation (Figure 9.9). The quality of models—i.e., how accu-
rately their predictions accord with real performance—depends on how well they repre-
sent the real problem situation, the material properties, the nature of the contaminants
involved, and processes involved. This requires not only proper and accurate problem
Transport and fate modeling
Transport and fate modeling
Risk
Risk of groundwater
and soil-site
contamination and
health threat.
Risk
Risk of groundwater
and soil-site
contamination and
health threat.
Design
Design of
containment
systems and
remediation
schemes.
Design
Design of
containment
systems and
remediation
schemes.
Forens
Determination o
contaminant sourc
and source-pathway
receptor connection
Forensic
Determination of
contaminant source
and source-pathway-
receptor connections.
(1) Problem conceptualization
Knowledge of problem and the various
processes controlling persistence and
fate of contaminants. Assumptions and
simplifications.
(2) Model and code development
Analytical description of system.
Conservation laws, continuity conditions,
constitutive relationships, solution
algorithms, numerical approximations.
(3) Calibration and verification
(4) Validation
Input data sets and parameters, reliabilities,
uncertainties, relevance, parameter
assignment, sensitivities, input-output flow,
verifiable situations, benchmarking, analytical
solutions.
Availability of long-term platform for validation
of performance? 50 years? 100 years?
Acceleration of chemical and biogeochemical
processes in laboratory tests and
simulations?
FIGURE 9.9
Principal objectives, issues, and requirements for contaminant transport and fate modeling.
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