A Practical Approach for Site Investigation - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 157

detected in the laboratory due to the fact that they might have been lost from the
sample (evaporation, biodegradation) or in the process of obtaining an analytical
sample (evaporation) prior to analysis. So when there is a clear indication of a misfit
between the observations in the field and the analysis, there might be a reason for
additional sampling and/or analyses.
The power of observations in the field by the sampler, like the previously
described “oil like smell”, has of course its limitations. Although the nose is a very
sensitive “detecting instrument”, it is also easy to obtain highly biased “measure-
ments”. The sensitivity of the nose is affected by the overall smell in the area,
becomes less sensitive after longer exposure periods and, moreover, the sensitiv-
ity will be very low when the sampler has a cold. Nevertheless, field observations
are important and have to be reported by the sampler. More important, however, is
the fact that smelling will expose the sampler to contaminants that might be highly
toxic. For this reason, organoleptic observations, apart from visual observations, are
to be prevented. Here again, there might be a role for screening techniques. Although
these techniques are less easy to operate than the nose, they are more quantitative
and objective and therefore easier for interpretation by the consultant who has to
write the report on the Exploratory Investigation.
When writing the report of the Exploratory Investigation, it is important to
include the observations of the sampler, the soil descriptions made and any indi-
cation of potential contaminations as observed in the field. Obviously, also the
analytical results are to be included in the report. All information mentioned pre-
viously can be considered as factual information. But at least as important is the
interpretation of that information in an enhanced and perhaps adjusted description of
the conceptual model of the site and its contamination. As mentioned for the report
of the Preliminary Investigation, the consultant has to make a clear distinction in the
report on the Exploratory Investigation between facts and the interpretation based
on that.
The hypothesis which was used to define the sampling strategy is to be tested
in light of the obtained results. Do the results indeed acknowledge the conclusions
of the Preliminary Investigation, or is there something different on the site? And
if there appears to be a difference, what does that imply for the further inves-
tigation of the site? Are the results conclusive enough to proceed to the Main
Investigation phase, or is an additional phase of the Exploratory Investigation nec-
essary to increase the reliability about the type and spatial distribution of the soil
contamination? Obviously, the latter can also be part of a first step of the Main
Investigation. However, the main purpose of the Main Investigation is to delin-
eate the contamination that was identified during the Preliminary Investigation
and of which the presence was affirmed during the Exploratory Investigation.
Contaminations that are not considered in these two phases, either due to a lack of
information in the Preliminary Investigation or due to missing the correct location
in the Exploratory Investigation, have an enlarged possibility of not being detected
in the Main Investigation. So before going into the phase of the Main Investigation,
it is important to be as sure as possible that all potential contaminations on the site
are identified.