Environmental Engineering Reference
In-Depth Information
samples and investigate them in their laboratory. Even if the assessment of a site
is well prepared at a preassessment stage and all existing information, historical
data and air photos have been collected, people of the area interviewed and the
conceptual model of the site has been prepared, it is still questionable if mea-
surements are necessary and if yes, for what. Clear identification of the objective
and an assessment plan are the prerequisites of site assessment. Measurements are
often needed only for the validation of the model-based results, but if very little
information is available about a site, the only possibility is a stepwise site assess-
ment with optimal tiering. The uncertainty in historical data and models based on
good quality data from former industries or mining (i.e., produced amounts, used
materials, applied technologies, etc.) may be lower than the uncertainty in new
assessment data. Uncertainty may be reduced by the application of a tiering in site
assessment: assessment of existing data and information as a first tier, screening
by measurements as a second tier, and a more detailed assessment tier based on the
result of the screening if necessary. The higher the number of the tiers, the lower
the uncertainty, but the time requirement may increase significantly. Uncertainty
also increases with the increase of time because of the changes during time shift
between the measurement steps. Uncertainty of site assessment may be reduced
by an in situ assessment, meaning in situ measurements and immediate decision
making on the next step of the assessment. This concept quasi multiplies the tiers
of the assessment without consuming any additional time;
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Assessments based on mathematical (computer) model calculations are more and
more widespread in contaminated site assessment and risk assessment. QSARs
are used for the prediction of the environmental fate properties of chemicals, as
well as the scale of their hazardous effects. The transport of a chemical substance
in the environment can be described if the characteristics of the chemical and
the target environment are known. Adverse effects of contaminated air, water
and soil can be estimated based on existing data by using models in the form of
equations. The evidence on the true or untrue nature of the model is the validation
by measurements. The measurements may support the results of the model or may
help to reduce the uncertainties in the model and improve it;
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The use of average values for risk management has both advantages and disad-
vantages, depending on the variability of the parameters whose average is used. If
the average is representative for most part of the target element, it can be applied,
but we must know that its use increases the uncertainties because of deviations in
the less conservative areas. On the other hand, worst-case estimation is an undue
reduction of uncertainty, generally resulting in high costs and withdrawal of funds
from more risky cases;
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Site assessment methods and their inadequate application imply uncertainties due
to conceptual misuse of the model and method, measurement errors, improper
evaluation, statistical evaluation and interpretation (the same primary data can be
evaluated differently). Extrapolation from measured data is burdened with uncer-
tainties. Further sources of extreme uncertainties are the lack of standardized
methods for chemical analysis and toxicity assessment, the lack of uniform tool
batteries for typical problems and site assessment cases, undeveloped tools in the
field of direct toxicity testing, improper or nonstandardized test organisms used
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