Identifying and Evaluating Impacts - Mining and the Environment: From Ore to Metal - page 428

reached its viable minimum. The minimum forest area that can support the bird popula-
tion then becomes the threshold against which the impact of land clearing associated with
the mining project is assessed.
Regulatory thresholds are generally more commonly used in identifying project impacts.
If regulatory thresholds exist, they are easily compiled. The threshold analysis is then sim-
ply reduced to a checklist which compares regulatory thresholds (e.g. emission and ambi-
ent standards) with the corresponding project information (expected project emissions and
expected change in environmental quality). Because pollutants affecting human health and
constituents in air and water are usually regulated, these thresholds are useful for assess-
ment purposes. Consideration of human health is often implicit in thresholds established
for bio-physical components such as air quality.
In practice, however, impact assessment is often hindered by a lack of thresholds;
which is particularly true for terrestrial components of ecosystems. Because of this, there
is not always an objective technique to determine appropriate thresholds, and professional
judgement must be used. In the course of an environmental assessment, and in the absence
of dei ned thresholds, the study team can either (1) suggest an appropriate threshold; (2)
consult various stakeholders, government agencies, and technical experts; or (3) acknowl-
edge that there is no threshold, determine the residual effect and its signii cance, and let
the reviewing approval authority decide if a threshold is being exceeded.
Qualitative Assessment
Often it is either impossible or impracticable to approximate nature simplistically using
models. In other cases, models would require more resources for their successful applica-
tion than could be justii ed by the project requirements.
CASE 9.5
The Importance of Considering Emission
and Ambient Environment Quality Standards
Question: Is the discharge of mine dewatering water with
a pH value of 7 into the aquatic environment acceptable?
It depends. If the aquatic environment is swamp or peat
water with a pH value of, say, 5, discharge of water of
excellent quality and a neutral pH of 7 will negatively
impact the natural ecosystem. It is the difference of
individual chemical characteristics between discharge and
ambient waters that is important, not only the absolute
values.