Environmental Engineering Reference
In-Depth Information
proponent. Similarly, small and otherwise inconsequential accidents may undermine
the credibility of a proponent and create serious social tensions and negative community
attitudes toward a project which may never be overcome.
Reversibility. Reversibility refers to the environmental recovery once an impact has
occurred. Irreversible environmental impacts are commonly considered more signii cant
than those that are reversible. Irreversible changes always command attention because they
signal a loss of future options. Species extinction, severe soil erosion, destruction of ancient
rain forest, and other habitat destruction are examples of irreversible changes. Change in
land use by providing access to remote areas is also virtually impossible to reverse once land
use changes commence (such as conversion of forest areas to agricultural land). If impacts
are reversible, it is important to understand the rate of recovery or adaptability of an impact
area. Groundwater pollution is generally reversible, but recovery may take several decades,
or longer. In practice, it can be difi cult to know whether the environmental effects of a min-
ing project will be irreversible or not. It will be important to consider any planned mine clo-
sure activities that may inl uence the degree to which environmental effects are reversible or
irreversible. Sometimes environmental change will be absolute, as in the extinction of a spe-
cies, while sometimes it will be absolute for all practical purposes, as in the case of landform
changes due to waste rock or tailings placement, which could only be reversed over a long
period of time and with unacceptable expenditure of money and energy.
Duration. This refers to the period over which an effect occurs. Long-term environ-
mental effects may be signii cant. In the case of a mine, there are a number of long-term
environmental effects. With few exceptions on-land waste rock and tailings storage facili-
ties are permanent structures designed to last hundreds or thousands of years. Open pits
also change the landscape permanently, except in rare cases where they are back-i lled.
Improvement of quality of life or education equally may last for generations. Short-term
environmental effects may also be signii cant, especially if the short-term effects negatively
affect public perception of a mine project. Community tension developed during explo-
ration or mine construction may haunt a mining project, even though the actual impacts
may have ceased long before.
Consideration should also be given to negative impacts that may develop over time. The
most common examples of delayed impacts are those associated with acid rock drainage
which may, in some instances, emerge after decades, sometimes after mine closure. Human
health impairment associated with exposure to trace metals released by mining activities may
also have latency periods of up to tens of years. Obviously, when considering future impacts,
questions regarding their likelihood, latency period and duration are all important.
Frequency. Closely related to the duration of the effect is its frequency. The frequency
of effects and the potential of the environment to recover from these effects are important.
If an activity is intermittent, for example, it may allow for environmental recovery during
inactive periods. A good example is turbidity. Many aquatic ecosystems have evolved in
situations where surface waters are intermittently turbid. Indirect effects of mining may
increase the incidences of turbidity, but if adequate intervals of clear water remain, the
important ecological functions of the ecosystem may be retained.
Geographic extent. The geographic extent is dei ned as how far an effect propagates.
Localized adverse environmental effects may not be signii cant, while widespread effects
may. Geographic extent takes into account the extent to which adverse effects, caused by
the project, may occur in areas far removed from it (e.g. the long range transportation of
atmospheric pollutants), as well as how they may contribute to any cumulative environmen-
tal effects. A single stream crossing, considered separately, may represent a localized impact
of small signii cance and magnitude; however, a number of crossings of the same stream
could result in signii cant downstream degradation of water quality. The deterioration
Irreversible changes always
command attention because they
signal a loss of future options.
The most common examples
of delayed impacts are those
associated with acid rock
drainage which may, in some
instances, emerge after decades,
sometimes after mine closure.
 
Search WWH ::




Custom Search