A Practical Approach for Site Investigation - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 159

account of the information necessary to enable specific types of remediation. When
for example in-situ bio-remediation is a possible and preferable option, the Main
Investigation should also provide information on the presence of bacteria in the
soil that can be stimulated and their need for nutrients and/or oxygen for enhanced
biodegradation of the contaminants. However, it is not always possible to predict
the potential remedial techniques in advance, while there might also be practical,
temporal or legal reasons not to focus (too much) on the information necessary
for the remediation. In those cases the Main Investigation has a focus on the
contamination.
More in general, and independent of the potential techniques that can be applied
to remediate the site, knowledge of the local geology, soil type and hydrology
are always of major importance. Not only because these characteristics will have
an important influence on the spatial distribution of the contamination, but also
because this information is essential for a good judgment on subsequent steps, both
in light of the continuation of the investigation, if necessary, as well as for later Risk
Management actions (e.g. remediation).
In general, the Main Investigation is, for the part of the investigation that focuses
on the contamination, highly comparable to the Exploratory Investigation. However,
instead of seeking confirmation of the presence of the contamination, the Main
Investigation should focus on finding the boundaries of the contamination in both the
horizontal and vertical directions. And apart from investigation of contamination in
the soil, the volume of groundwater that is contaminated must be determined. Apart
from defining the delineation, it is also relevant to obtain information on the concen-
trations that can actually be found in the “hot spots”, as these might also determine
possible options for dealing with the contamination.
Finding the boundaries of the contamination and at the same time obtaining
additional information necessary for potential remedial actions, will often need
a number of subsequent steps in the Main Investigation. The number of steps
necessary depends, of course, on the size of the contamination, the distance between
sampling points in the various phases, the complexity of the contamination on the
site, the level of detail needed in light of potential remediation techniques, as well
as the use of additional information, like the results of field screening methods.
Consequently there cannot be a simple guideline on how the goal of the Main
Investigation can be reached as efficiently as possible.
Obviously, after each step, the investigator has to take account of the obtained
results when planning additional sampling. More specifically, the obtained results
are to be compared with the hypothesis (or a combination of hypotheses) on the con-
tamination that forms the basis of the investigation. If in a specific step the results
deviate from the hypothesis, a definition of an alternative hypothesis might be nec-
essary, which would result in a better guidance for additional sampling steps. Again,
the consultant should make a clear distinction between facts (e.g. analytical results,
field observations) and interpretations (e.g. which samples are actually analysed,
what is concluded on the obtained results).
After each step of the Main Investigation, the conceptual model of the contamina-
tion and the site becomes more detailed. Still, even when a large number of samples