Assessing Environmental Impact 17and indirect impacts owing to regional development, housing, lifestyle, and economic
development.
The checklist technique thus lists all of the pertinent factors; then the magnitude
and importance of the impacts are estimated. Estimated importance of impact may be
quantified by establishing an arbitrary scale, such as:0 = no impact
1 = minimal impact
2 = small impact
3 = moderate impact
4 = significant impact
5 = severe impactThe numbers may then be combined, and a quantitative measurement of the severity
of the environmental impact for any given alternative be estimated.
In the checklist technique most variables must be subjectively valued. Further, it
is difficult to predict further conditions such as land-use pattern changes or changes in
lifestyle. Even with these drawbacks, however, this method is often used by engineers
because of its simplicity. Impact assessments of controversial projects often do not use
the checklist technique because the numerical ranking implies a subjective judgment
by the environmental assessment team. A checklist remains a convenient method for
developing a FONSI, although a FONSI requires subjective selection of the number
judged to be the lowest value of significance.
EXAMPLE 2.1. A landfill is to be placed in the floodplain of a river. Estimate the impact
by using the checklist technique.
First the items to be impacted are listed; then a quantitative judgement concerning
both importance and magnitude of the impact is made. In Table 2- 1, the items are only
a sample of the impacts one would normally consider. The importance and magnitude
are then multiplied and the sum obtained.Table 2-1.
Potential impact Importance x magnitudeGroundwater contamination 5~5=25
Surface contamination 4x3=12
Odor lxl=l
Noise 1x2=2
Jobs provided
Total 34-2 x 3 = -6
This total of 34 may then be compared with totals calculated for alternative courses of
action. Note that jobs are a positive impact, as distinct from the negative environmental