Conducting the Environmental Impact Analysis and Assessment - Environmental Impact Analysis: Process and Methods - page 220

A major advantage of integrating mitigation into the full environmental
impact analysis process is in the alternative comparison process. The impacts
of an alternative can be very different with and without mitigation, as can the
costs. Take for example, an alternative that has many benefits and much lower
costs but results in significant traffic that causes serious safety concerns for an
adjacent school with a large pedestrian population. This alternative might not
be selected or even screened out early in the process because a critical pub-
lic safety significance criterion was exceeded. But formulation of an additional
alternative incorporating public safety mitigation such as a relatively inexpen-
sive pedestrian overpass, electronically controlled crosswalk, or other mea-
sures to meet the public safety significance criteria could be the alternative with
the least cost, most benefits, and fewest impacts. There are numerous similar
examples where “fatal flaw” wetland impacts can be avoided by incorporat-
ing well-designed, constructed, and monitored created wetlands as part of the
alternative.
Another advantage of the integrated approach to impact mitigation is
that it takes into account the complexity of environmental factors contrib-
uting to an impact or existing conditions. If for example there is a predicted
impact on a fisheries population resulting from an increased silt load to the
river, mitigation of the siltation impact alone may have no actual benefit
(Erickson 1994). There may be other existing factors such as habitat limita-
tions, food availability, and breeding locations, which are already limiting
the fish population density or distribution. Therefore, changes in silt load
or the resulting suspended sediment concentration would not have any
effect on the fish population. Similarly, if there are predicted impacts from
an alternative resulting from both reduction in dissolved oxygen concen-
tration and silt load, mitigating just one of these factors would not produce
any benefit. Including mitigation in the full environmental impact analy-
sis, rather than adding it after the fact would expose such false benefits
and they could be integrated into the alternative comparison and other
decisions.
The downside of the integrated approach to mitigation is that it can
result in an unwieldy and repetitive evaluation of alternatives. This issue
can sometimes be addressed at the alternative screening stage (see Section
4.5.3) by eliminating alternatives in a side-by-side comparison. If the com-
parison reveals that the two alternatives have generally the same bene-
fits and adverse impacts but substantially higher costs, the one with the
higher cost can be eliminated at the screening stage. Another approach to
addressing the complexity of alternatives created by integrating mitiga-
tion into the full analysis is to identify and evaluate alternatives sepa-
rately for independent segments of a project, plan, or program (see Section
6.3.1). With this approach, the superior alternative(s) for each component
of the action can be combined into a manageable set of comprehensive
alternatives.