Environmental Engineering Reference
In-Depth Information
social, and economic systems, as well as reputation. The rating of risk consequences will
depend on the highest risk in each of these four aspects.
Evaluating the consequences of a risk is not very different from evaluating the signii -
cance of environmental impacts. As is true for assessing impacts, the complicating issue for
environmental risk assessment is the lack of an easily dei ned measure of what constitutes
harmful consequences for the environment. In some cases dei nitions of environmental
damage are intuitive or are laid down in statute (e.g. loss of life or violation of regulatory
standards); in others appropriate criteria need to be based on professional judgements.
How do environmental impacts identii ed in an EIA link into the risk assessment
matrix? The best way to visualize the link is to understand these impacts as the conse-
quences of risks that fall into the category 'will occur/with certainty'. Environmental
impact assessment studies are concerned with environmental hazards that are certain to
occur. In mining the generation of waste rock and tailings, as one example, is certain, so is
the disturbance of land and water. Engineering and management efforts are designed to
eliminate hazard-related environmental consequences entirely (that is moving the prob-
ability of occurrence into the category 'unlikely'), or if impacts are unavoidable, to move
potential environmental risks into the lower left corner of the risk assessment matrix by
reducing the magnitude of the consequences of the occurrence. As such, environmental
management measures aim either to eliminate hazards, to reduce unavoidable environ-
mental consequences to an acceptable level, or both (
Figure 9.15
). This begs the question:
What is an acceptable environmental risk?
Evaluating the consequences of
a risk is not very different from
evaluating the signifi cance of
environmental impacts.
Environmental management
measures aim either to eliminate
hazards, to reduce unavoidable
environmental consequences to
an acceptable level, or both.
Risk Acceptability
The boundaries of risk acceptability are not clearly dei ned and are tailored to the fac-
tors inl uencing the signii cance of the risk. Clearly risks that are situated in the lower
right corner of the risk assessment matrix (risks occurring frequently with catastrophic
consequences) are not acceptable. Risks in the upper left corner of the matrix are more
acceptable, as (1) risk occurrence is unlikely and (2) risk consequences are negligible. The
acceptability of risks that fall between these two end points depends on a variety of factors;
some follow.
FIGURE 9.15
Using the Risk Assessment Diagram to
Illustrate the Aim of Risk and Impact
Mitigation Measures
RISK MITIGATION
Low
High
RISK CONSEQUENCES
Low
Risk is Usually
Acceptable
Risk
Acceptability
Boundary
Avoid
Project is not
Acceptable as
Proposed
Mitigate
High
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