Environmental Engineering Reference
In-Depth Information
Local soil contamination implies that a specific process is expected to have had
an adverse affect on a specific location. This was not necessarily a small area, but
obviously, when the area gets bigger the contamination within that area will appear
more or less as diffuse contamination. The practical distinction between these two
types of contamination therefore is that on the scale of the investigation, only a part
of the site is contaminated when it is considered to be local soil contamination, while
the whole site and more will be contaminated when it is diffuse soil contamination.
But also the contaminating process will determine if the contamination is to be
considered local or diffuse.
Finally, a third assumption deals with the more detailed expectations of where
the contamination can be found. For local soil contamination, the contamination has
either a:
•
Known position of the core of the contamination.
•
Unknown or unsure position of the core of the contamination.
For a diffuse contamination, the contamination is either:
•
Homogeneously distributed.
•
Heterogeneously distributed.
•
The boundaries of the contamination are unknown or uncertain.
As a consequence, there are different types of diffuse soil contamination. A
contaminating source at some distance, for example stack emissions, might result
in a contamination in the top soil where little variation is expected between indi-
vidual locations on the site. The contamination, originating from a diffuse source,
can be considered as homogeneously distributed. But when harbour sludge is used
in embankments, large differences on a small scale can be expected. However,
that same expectation on variability and contaminants applies for every location
in that embankment and therefore the embankment as such can be considered as
diffuse, but heterogeneous, contamination. Finally, diffuse contamination, being
either homogeneous or heterogeneous, might have boundaries that are relevant on
the scale of the investigation. In these situations, finding the boundary of the contam-
ination is in principle more relevant than investigating the variation in concentrations
within the contaminated spot.
The Preliminary Investigation ends with the assumptions on the presence and
spatial distribution of the contaminants in soil and/or groundwater. These assump-
tions are formalized in national and international standards in hypotheses which are
used as a basis for starting the Exploratory Investigation.
3.7 Exploratory Investigation
The Exploratory Investigation is, after the site visit during the Preliminary
Investigation, the second time that the site is actually visited. However, it is the
first time that samples will be taken. Prior to sampling, first a sampling strategy
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