Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 78

have a common background, that is, academic study in a related technical field,
the interest and mentality of both groups is often very different. Moreover, optimal
co-ordination requires frequent communication, which is hampered by a physical
separation of working places. Even more importantly, mutual communication is not
implicitly productive and the significance of it, therefore, is often underestimated.
Souren ( 2006 ) investigated the role of scientists and policy makers in the
derivation of Soil Quality Standards in the Netherlands in the period 1971-
2000. She concluded that in general policy makers do have sufficient scientific
knowledge to understand the scientific procedures used to derive Soil Quality
Standards. At the same time, the author concluded that most scientists understand
policy-making.
1.10.4 The Risk Assessor
Risk Assessment is often said to be the scientific part of the contaminated site
management framework and an objective procedure. That might be true for a large
part. However, compared to other scientific disciplines, Risk Assessment involves
quite as many subjective decisions. An important example of a subjective judge-
ment is the interpretation of measured soil concentrations, certainly in the case of
heterogeneously contaminated sites. One risk assessor might focus on the highest
measured value, while another assessor will use the average of all samples in the
Risk Assessment. In the latter case, it might make a difference whether this individ-
ual decides on the arithmetic or geometric mean, which might differ with a factor
of up to 10. Ideally, these decisions are protocolised. However, using margins in
many decisions (such as the decision on which value to take for the 'representa-
tive soil concentration' in the example shown above) could actually improve the
Risk Assessment. For example, in an early tier of Risk Assessment and when the
risk assessor's estimate is that risks are acceptable, the risk assessor might delib-
erately focus on the highest concentration. In that case, the most likely outcome
is 'risk acceptable and case closed', on the basis of a limited effort and budget. In
other cases, for example, when the layout of the site shows different uses such as
green shoulders and paved areas at a business park, the risk assessor might derive
an average representative concentration, only valid for the green shoulders. In this
case, since no vegetables will be cultivated on the shoulder, this average soil con-
centration will be good enough to investigate the possibilities for the development
of typical shoulder vegetation. Using the margins in an intelligent and responsible
way, in fact, makes Risk Assessment a creative and challenging process.
The risk assessor needs to accompany the technical Risk Assessment with three
very important activities. First, the risk assessor should always relate the purpose of
the Risk Assessment to the choices he or she has to make. Second, the risk assessor
should incorporate uncertainties in every step of the Risk Assessment. Third, and
last but not least, the risk assessors should make every choice, as well as the exact
meaning of the Risk Assessment results, transparent. Moreover, during the whole
process, communication with decision-makers and stakeholders is essential.