Environmental Engineering Reference
In-Depth Information
one and only investigation phase where actual samples are taken and analysed.
The Exploratory Investigation can also be the only investigation phase in situations
where a decision is to be made about whether to buy a site.
Thus, the Exploratory Investigation should be sufficiently intense to be able to
conclude that further investigation of the site is not necessary. So again from this
perspective, defining the effort to be put in the Exploratory Investigation is finding a
balance between the costs for the investigation and the quality and acceptable “level
of proof” provided by the Exploratory Investigation.
The fieldwork for the Exploratory Investigation is based on the hypotheses as
defined in the Preliminary Investigation. In simple situations a single hypothesis
describes the expected contamination and can be used to investigate the site. An
example is a site where there is an underground storage tank for mineral oil present
in the soil and the objective of the investigation is to determine if that tank is leak-
ing or has contaminated the soil. The hypothesis in this particular situation is that
there is a local soil contamination with a known location. A limited number of bor-
ings, covering both the direct surrounding of the tank, the pipes connected to it and
the feeding pipe, will provide sufficient evidence for acceptance or rejection of the
hypothesis.
In more complex situations, combinations of various types of contamination
might be present. Contaminations with different type of contaminants, different
processes that caused the contamination and differences in spatial distribution of
the contaminants. Additionally, there might also be a need to obtain a more general
impression of the soil quality of the whole site, a goal that can also be part of the
Exploratory Investigation. Obviously, these goals are not to be dealt with separately.
A combination of sampling strategies for the individual hypotheses to be tested, can
result in a more cost-effective approach for the investigation, without losing quality
for each individual hypothesis.
As discussed previously, the number of borings, samples and monitoring wells
as mentioned in the Dutch standard, cannot be regarded as the true and only answer.
At the same time, these strategies can be seen as exemplary for what can be used for
the different hypotheses, in every part of the world.
The Dutch standard for the Exploratory Investigation identifies the sampling
strategies for the following types of sites:
•
Unsuspected site.
•
Large scale unsuspected site.
•
Suspected site with local soil contamination with known location.
•
Suspected site with one or more underground storage tanks.
•
Suspected site with homogeneously distributed diffuse soil contamination.
•
Suspected site with heterogeneously distributed diffuse soil contamination.
•
Suspected site with unknown soil contamination.
•
A baseline investigation for future potential contaminating activities (defining the
soil quality prior to the soil use that might have an adverse affect).
•
A baseline investigation for future underground storage tanks.
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