Identifying and Evaluating Impacts - Mining and the Environment: From Ore to Metal - page 444

Impact Assessment Methodologies and Objectivity

When evaluating impacts, quantitative methods are usually preferable to qualitative meth-
ods as they are more precise, outcomes are reproducible, they do not contain subjective
views, and often, outcomes can be linked to numerical standards. In an ideal situation, use
of quantitative methods allows a baseline parameter to be measured using a numerical
scale (such as ambient concentration of a trace metal in water), and impact prediction to be
made using a scale that relates to the existing baseline (predicted maximum concentration
of a trace metal in water), facilitating the evaluation of its signii cance. This is particularly
ideal if the impact can be evaluated against a numerical standard (say maximum permis-
sible concentration of the trace metal under consideration). Quantitative methods apply
particularly to physical and chemical environmental aspects such as air quality, which
would be hard to express in any meaningful way other than by using a quantitative
approach. By expressing existing and predicted air quality levels and the relevant stand-
ard as, for example, micrograms per cubic metre, the magnitude of the predicted impact
over the existing baseline, and its signii cance in the context of the standard, can be clearly
stated.
A quantitative approach also facilitates discussions between the mining company and
its stakeholders in the new mine project. It is easier to explain that efl uent discharge will
conform to a given discharge standard than to articulate how landscape quality will be
affected by mining. In addition trade-offs between reductions in environmental impacts
and associated costs are inherently easier to understand if costs relate to measurable envi-
ronmental gains. The effectiveness of different abatement technologies in reducing gas-
eous emissions and hence in improving ambient air quality can be readily assessed and
compared with associated costs. This contrasts with cost estimates for implementing miti-
gation measures to reduce the impact on landscape quality or visual amenity. It may be
possible to assign a cost to the measure (for example rehabilitation); it is much more dif-
i cult to assess the resulting impact reduction.
Notwithstanding their benei ts, quantitative methods do not provide a total panacea for
ensuring objectivity in environmental assessment.
Data collection and modelling effort can be disproportionate. Quantitative methods are often
resource-intensive, involving extensive data collection and careful interpretation of model
results. In contrast, expert judgement, while subjective, can be reached relatively quickly,
and often i ts the purpose. Some cases of acid rock drainage illustrate this point. Despite
pre-mining investigations involving several hundred geochemical tests to assess acid
rock drainage of waste rock, some projects have found that the actual incidence of ARD,
in practice, has been much higher or lower than predicted by the quantitative pre-min-
ing studies. Various reasons have been postulated for this, but in general, there have been
incorrect classii cations and correlations of different lithological units, which only became
clear when mining provided large exposures, enabling the geology to be properly inter-
preted. In at least one such case, the mine planners would have been better advised to
assume that all waste would be acid-generating, rather than attempting to implement a
strategy to separate, selectively place and treat a range of different materials.
As a completely different example, mine development may partly affect breeding grounds
of commonly encountered bird species in the host region that are classii ed as neither threat-
ened or endangered. A complete quantitative impact assessment would involve a wide range
of studies and research, and may be disproportionate to the signii cance of the impact. In
such cases, professional judgement may be sufi cient to advise on impact signii cance, and to
propose effective mitigation measures.

It is easier to explain that effl uent
discharge will conform to a
given discharge standard than to
articulate how landscape quality
will be affected by mining.

Expert judgement, while
subjective, can be reached
relatively quickly, and often fi ts
the purpose.