Environmental Engineering Reference
In-Depth Information
The cost function develops weights that
convert scores expressed in different units into
an overall score expressed in uniform monetary
terms.
S
ij
scores considered for the cost function
must be expressed in units of impacts that can be
directly quantified economically from a mitigation
perspective. There is no artificial performance
value in this case. The decision matrix
A
remains
unchanged, and weights are used at the aggregation
stage. The mitigation cost function
c
is defined
as follows:
dresses this issue by assuming that all negative
impacts will have to be mitigated at a certain cost.
The optimal alternative would therefore be the
one that minimizes the overall mitigation costs.
In certain cases, specific thresholds are not to be
exceeded in order to comply with safety and health
requirements. Our methodology acknowledges
this by allowing for environmental limits to be
included in the evaluation process by allowing
for the inclusion of Critical Threshold Values
(Table 8, Table 9).
c S W c S W
j
:
→
: (
)
=
Aggregation and Ranking
j
The last step of our evaluation method is the inte-
gration of all previous steps for the selection of the
most environmentally sustainable option. The core
method uses a weighted additive procedure for the
aggregation of individual scores and the ranking
of alternatives. End-users may take advantage
of the method's flexible structure by computing
sub-rankings for particular criteria clusters in order
to assess the performance of alternatives under
specific criteria. Weights determined using the
cost function paradigm are directly used in the
last step whereas for the other criteria, end-users
can choose between not using weights (i.e. all
criteria being equal with weights equal to 1) or
determining arbitrary weights on a case-by-case
basis to respond to local challenges, threshold
values, stakeholder pressure, etc. If the number
of criteria is limited, pairwise comparisons may
be used to limit the possibility of biases. The final
decision matrix (Table 10) with its associated
weights becomes:
The aggregated performance of the evaluated
system is defined by two values. The first is the
utility performance
UP
i
of alternative
i
and defined
as the weighted sum of utility values
U
ij
for all
utility-based criteria with the weights
W
j
deter-
mined arbitrarily. The second is the cost perfor-
mance
CP
i
of alternative
i
and defined as the
weighted sum of physical and quantitative scores
with j = 1,2,..m the number of criteria,
S
the set of
physical performances and
W
, the set of weights
representative of mitigation costs.
The key theoretical concept of this chapter
is the use of cost functions to derive weights for
quantitative criteria. Such cost functions must
be defined on a case-by-case basis by analyzing
historical mitigation costs on the same airport
compound or at other airport developments of
comparable characteristics. In this chapter, we
present an initial numerical example (Box 2) for
the weighting of aircraft emissions to illustrate
this process. This procedure can be similarly ap-
plied to other impacts such as noise and wildlife.
Mitigation costs for noise typically include com-
pensations paid to neighboring communities for
improving housing acoustic insulation. Wildlife
mitigation costs often enable the development of
endangered species protection program onsite,
their relocation offsite or the sponsorship of other
wildlife protection programs. Data for a variety
of mitigation measures are relatively accessible
by end-users of the method.
Users should also be aware that measures to
reduce environmental hazards may have negative
side effects. For example, technical measures to
reduce GHG emission from airplanes may increase
NO
x
emissions and noise. Our methodology ad-
