Impact prediction, evaluation and mitigation - Introduction to Environmental Impact Assessment - page 160

• Other compensation and
enhancement
( Source: DETR 1997.)
classification of mitigation, adopted in the project, by levels of mitigation, mitigation
hierarchy and project phase. The levels relate to broad decisions that are made during the
design of a project, with the last two reflecting the fact that effective mitigation can be
achieved through measures other than physical ones. The mitigation hierarchy focuses on
the principle of prevention rather than cure where, in principle at least, the options higher
in the list should be tried before those lower down the list. The project phases relate to the
life cycle of the project first discussed in Chapter 1. Any particular mitigation measure
can be classified in a combination of the three ways—for example, physical design
measures can be used to minimize an impact at source, during the construction phase
(DETR 1997).
5.4.2 Mitigation in the EIA process
Like many elements in the EIA process, and as noted in Table 5.11, mitigation is not
limited to one point in the assessment. Although it may follow logically from the
prediction and assessment of the relative significance of impacts, it is in fact inherent in
all aspects of the process. An original project design may already have been modified,
possibly in the light of mitigation changes made to earlier comparable projects or perhaps
as a result of early consultation with the LPA or with the local community. The
consideration of alternatives, initial scoping activities, baseline studies and impact
identification studies may suggest further mitigation measures. Although more in-depth
studies may identify new impacts, mitigation measures may alleviate others. The
prediction and evaluation exercise can thus focus on a limited range of potential impacts.
Mitigation measures are normally discussed and documented in each topic section of
the EIS (e.g. air quality, visual quality, transport, employment). Those discussions should
clarify the extent to which the significance of each adverse impact has been offset by the
mitigation measures proposed. A summary chart (Table 5.12) can provide a clear and
very useful overview of the envisaged outcomes, and may be a useful basis for agreement
on planning consents. Residual unmitigated or only partially mitigated impacts should be
identified. These could be divided according to the degree of severity: for example, into
“less than significant impacts” and “significant unavoidable impacts”.