Identifying and Evaluating Impacts - Mining and the Environment: From Ore to Metal - page 427

The study of ecology is a well-established and broad discipline. The reader is referred to
Jorgensen (1994) for authoritative subject discussions.

Visual Modeling

Modelling of the visual impacts of a project on the surrounding area can be achieved
through the creation of photomontages. These can be generated manually or on a computer
using GIS software and can provide an idea of the overall visual impact on the landscape.
The assessment will, however, be subjective as it is not possible to express visual impact on
the landscape in numerical terms.

Threshold Analysis

Threshold analysis is based on the assumption that thresholds exist in most ecological sys-
tems, specifying limits in an environmental medium (predominantly but not to limited
to air and water) that must be not exceeded, or levels of environmental quality that must
be maintained. Thresholds may be expressed in terms of goals or targets, standards and
guidelines, carrying capacity, or limits of acceptable change, each term rel ecting differ-
ent combinations of scientii c data and societal values. Regulatory thresholds may change
in time, especially in developing countries where institutional settings are still in their
infancy. A threshold can be a maximum concentration of a certain pollutant beyond which
health may be adversely affected, a maximum number of hectares of land cleared from its
existing natural state before visual impacts become unacceptable, or a maximum number
or proportion of animals lost from a habitat before the viability of the population is threat-
ened. Other examples of environmental threshold limits are ambient environmental
standards set by governments dei ning the degree of environmental quality that must be
maintained in an environmental resource to support its continued benei cial human use.
While often set to protect human health, thresholds may also be set to ensure long-term
sustainability of an environmental resource or any other resource considered worthwhile
to maintain. Examples are limiting the number of visitors to a natural recreation area (rec-
reational carrying capacity), or to a mining area (operational carrying capacity). In a social
context, carrying capacity could mean the limits of development that existing public infra-
structure can support, or limits of newcomers into an area that can be integrated with-
out changing the existing social fabric. Emission standards represent yet another group
of threshold limits dei ning the maximum acceptable quantity and/or concentration of
pollutants that may be discharged into the environment.
Threshold analysis is best suited to situations where regulatory thresholds exist. By
identifying regulatory thresholds, the mining project can be systematically assessed in
terms of its environmental impacts in relation to established regulatory carrying capaci-
ties. Impacts due to project emission are said to be acceptable (no signii cant impact) if
they meet regulatory emission standards. However, subsequent quantitative assessment
may still be required to predict changes in the receiving environment which may or may
not indicate a violation of regulatory ambient environmental standards for environmental
resources ( Case 9.5 ).
Project-specii c thresholds can be developed for site-specii c critical environmental
parameters. The remaining forest area within a valley, for example, could constitute the
controlling factor in determining whether the population of a certain bird species has

Thresholds may be expressed
in terms of goals or targets,
standards and guidelines, carrying
capacity, or limits of acceptable
change, each term refl ecting
different combinations of
scientifi c data and societal values.

Threshold analysis is best suited
to situations where regulatory
thresholds exist.