Management of abandoned and contaminated land - Environmental Deterioration and Contamination: Problems and their Management - page 185

Risks deliberately taken by workers and highly controllable by occupational safety
measures should be distinguished from imposed risk of natural or anthropogenic origin
on unprepared human receptors.
Risk assessment for the purpose of ranking contaminants or contaminated sites
should be distinguished from risk assessment for decision-making. A qualitative or
relative risk assessment is suitable for ranking, but to make decisions based on the
ranked sites or on one single site requires quantitative risk values, which can be handled
together with socio-economic values by the decision makers.
The risk assessment of a contaminated site is based on the information obtained
from site assessment, which is determined by the problem (hazard) identification and
by the conceptual model that identifies sources, pathways and receptors. Based on the
conceptual model one can identify the risk components to be assessed. Site assessment
and the collection of archive and measured data serve as direct information source for
the calculation of the quantitative scale of risk. This quantitative value can be used
for decision-making. Site assessment and risk assessment are in an iterative relation;
that is, the more precise the data from the data collection and site assessment are, the
closer the risk value will reflect reality.
It is essential to have a right risk assessment concept because it makes the whole
procedure feasible and easy to handle. Calculation of the RCR can start with a few
data, applying a conservative approach, i.e., overestimation in the case of uncertainty.
If RCR is less than 1, no action is needed; if greater than 1, a new iteration cycle starts
with more precise data and information. The steps are generally organized into groups,
representing “tiers'' in the risk assessment tool box. This tiered and iterative process
is both ecologically and economically efficient because the existing funds are used for
the assessment and management of high-risk cases; the no risk or less risky ones drop
out at an early stage.
Risk-based management of contaminated sites means assessing and handling the
risks of individual contaminants separately. The calculations/estimations are per-
formed always for one chemical substance. We calculate the total risk from the
individual components by simple addition or by weighted summation. Usually, risk
calculation is made only for the main or the most hazardous components of the mix-
tures, assuming that the minor components disappear faster, or have negligible effect;
though this is not true in a number of cases. If the identification of the contaminants
is impossible, the scale of risk reduction can be estimated by direct effect assessment.
A soil, for example, with an unidentifiable mixture of contaminants, which shows
high toxicity rate in environmental toxicity tests, can be considered risky. If it shows a
100-fold toxicity compared to the harmless dilution of the same soil ( RCR 100), risk

reduction should also be 100-fold to reach a “no-effect'' concentration. 100-fold risk
reduction is an effect-based target, which can be fulfilled by remediation and controlled
by environmental toxicity testing.

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5.3 Risk reduction and remediation of contaminated land
Based on the quantitative results of risk assessment, a series of decisions can be made:

- Is risk reduction necessary at all?

- What kind of risk reduction is feasible: prevention, restriction, remediation?

- What type and concretely which remedial technology to apply?