Environmental Engineering Reference
In-Depth Information
calibration is the process of adjusting the model geometry or input parameter val-
ues so that the model output matches conditions at a certain site. In developing a
strategy for model calibration, decisions are needed on whether calibration should
be steady state, transient or both, what data are to be matched and what input
parameter values must be adjusted to achieve calibration. Validation is the process of
determining how well the fate and transport model describes actual system behavior.
Validation of the model can be performed by matching model output to measure-
ments. According to ASTM 1999, an analytical model can be validated by comparing
model output to independent calculations of the output values (e.g., calculations using
a different “reference'' model). Numerical models used to predict spatial and time-
related changes in dissolved constituent concentrations can be validated by determining
concentrations of dissolved constituents at locations where initial concentrations are
not known and by time-series sampling at locations where initial conditions are
known.
4.1 Transport and fate modeling of point
source pollution
Most of the fate and transport models are conceptually simple and designed to estimate
the contaminant impact from a point source on groundwater, soil, surface water, air
and on all of them together. They consider the contaminated site/source individually
and focus only on predicting plume concentrations at a local scale but do not per-
mit prioritization of sites/sources at larger scales (Troldborg, 2010). Watershed-scale
transport models from point sources can in principle be used to evaluate the impact
on any kind of downstream receptors, for example, on rivers and streams (McKnight
et al.,
2010).
The calculation process of site assessment using transport models is as follows:
1
Source
→
E
source
(C
source
)
→
transport and fate modeling
→
PEC
compliance
2
PEC
compliance
> EQC
compliance
→
target
→
pec
compliance
≤
EQC
compliance
,
where:
-
E
: emission;
-
C
: concentration;
-
PEC
: predicted environmental concentration;
-
EQC
: environmental quality criterion;
-
Upper case: high concentration, unacceptable value;
-
Lower case: low concentration, targeted value;
-
→
: next step.
The model aims at answering the question: where does the pollutant go to and
how much is its concentration at a certain time and in a spatial point. The simplest
way of modeling the transport of a contaminant from a point source is based on the
difference between the contaminant concentration in the source and in the compliance
point. Assuming a constant water flow (river), the concentration of a chemical sub-
stance deriving from a point source can be calculated from the amount of the emitted
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