A Practical Approach for Site Investigation - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 149

If more precise information is available, a combination of old and new maps
is an interesting option as, by this combination of maps, potentially affected loca-
tions can be pinpointed more precisely. This is specifically favourable if the use
of the site has changed considerably over the years, for example where a for-
mer industrial site has already been used as a residential area for a number of
years.
The first impression of the investigator is known as the “conceptual model”. As
said, at first the conceptual model will be no more than a sketch and the term might
indicate a much higher level of detail than is actually reached. However, it is the
conceptual model of the site and its contamination that will be maintained, enhanced
and adjusted over the various phases of the investigation, until it has reached such
a degree of detail that it is sufficient in light of the Risk Management activities that
will be performed on the site.
To establish a first conceptual model based on the Preliminary Investigation, a
number of questions are to be answered. These questions are, for example:

• What processes happened on the site?

• On which exact locations did these processes take place?

• Which contaminants were involved in these processes?

• Through which mechanism might these processes have had an adverse effect on

the soil quality?

• Were there protective measures on the site at the time when these processes took

place?

• What is the effect of the local geological situation as well as the local hydro-

logical situation in relation to the potential spatial distribution of contaminants
(occurring transport processes)?

• Where (horizontal and vertical) is the most likely location of the contamination?

• Is the contamination only expected to be present in the soil, or also in the

groundwater?

The investigator should bear in mind that soil contamination is not per defini-
tion caused by accidental spillage or leakage. For former industrial processes, or
for current industrial processes in countries where the environmental legislation is
yet insufficiently developed, deliberate dumping of contaminated substances in, for
instance, soil or sewage water, was and is an accepted process of dealing with waste
materials. These (formally) accepted ways of dealing with wastes, might have (had)
an important adverse effect on soil quality.
Performing a Preliminary Investigation implies that one has to visit the site. A
site reconnaissance is considered an essential step in the Preliminary Investigation as
the investigator can experience the current situation at the site. This is also relevant
for the later Exploratory and Main Investigation, for example to investigate where
samples can be taken and where not. The site reconnaissance provides, in addition
to already available maps and/or photo's, essential information on the current state
of the site and its buildings. Often this provides important clues to where contam-
inating activities might have taken place. See for example Fig. 3.4 where dumped