A Practical Approach for Site Investigation - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 145

based on the Preliminary Investigation. The number of boreholes and monitoring
wells in this phase is limited in order to obtain a cost-effective first indication of
what actually is the soil and groundwater quality status of the site.
Three potential results can be obtained from the Exploratory Investigation:

• The expected contamination has indeed been found, or the expectation that there

is no contamination on the site is acknowledged; in each case the assumption
of the soil and groundwater quality of the site is confirmed in the Exploratory
investigation.

•

The expected contamination has not been found and thus the assumption of the
soil and groundwater quality is denied.

•

A different, not expected, contamination is found.

Clearly all three options will have quite different consequences for the conclu-
sions of the Exploratory Investigation and the potential further steps, which will be
discussed in more detail in Section 3.7 . In general, however, if a contamination has
been found, it is necessary to obtain more information on that contamination, and
fulfilling the technical goals as described in Section 3.4 becomes necessary. This
implies that a Main Investigation will be necessary. Obviously, part of the focus of
the Main Investigation is to obtain detailed information on the spatial distribution
of the contaminants. However, to what extent there is a need for that detailed infor-
mation will depend on the Risk Management solution, e.g. the remedial action, that
will be performed. See also the example in Section 3.3 . So the Main Investigation
will be an iterative process, where after each step, the question has to be answered
if the available information is “fit for purpose”.
These three phases will be discussed in more detail in the next sections.

3.6 Preliminary Investigation

As mentioned in Section 3.5 , the Preliminary Investigation is in fact the most
important phase of a site investigation. When no or insufficient information for the
site is obtained in this phase, it is highly likely that samples obtained during the
Exploratory Investigation will be taken at wrong locations and consequently might
provide a highly biased impression of the soil quality! Sites that are contaminated
with highly toxic contaminants might be considered uncontaminated due to the large
spatial variation often observed in soil. Assumptions on the type and spatial distri-
bution of the expected contaminants are therefore of major importance as it will
be neither financially nor technically possible to define an effective investigation
strategy without assumptions.
Assumptions on the potential contamination of the soil and groundwater are
based on knowledge of the (former) activities and processes on the site and are
to be combined with knowledge of the local geological and hydrological situa-
tion. Figure 3.2 shows the gas purification building of a former gasworks site in