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Sustainability Report 2015 79
The proposed Stockman Project is located in the high alpine
region of East Gippsland, Victoria, within the State Forest
area and with tenements bordering the National Park. The
project area contains steep topography ranging in elevation
from 600–1,200 metres above sea level. It straddles a
surface water divide that includes the headwaters of
the Tambo River, which flows south to the ecologically
important Gippsland Lakes on the south coast, and part
of the Goulbourn-Murray system to the north-east, which
has significant ecological, urban water supply and farmland
irrigation values. It is therefore critical that the project be
operated to minimise water use, and to protect ecological
values of the catchments in which it is located.
Because of the location high in the watersheds,
establishing large dedicated project water supply dams is
neither practical nor likely to be approved under Victorian
law. The very low permeability or ‘hydrogeologically-tight’
ground at site means that reliable groundwater supplies
are unlikely to be present. Therefore, during development
of the project, a number of other water supply options
were examined including extraction from:
•
distant rivers
•
distant commercial water supply dams
•
dedicated offsite borefields (which would need to be
developed).
In conjunction with this work, close attention was also
paid to minimising water use by the project, and to
capturing and reusing as much process water as possible
– given that 80% or more of water use is for ore crushing
and processing, discharged in tailings disposal, and is
potentially recoverable.
Detailed water balance modelling was carried out during
the project design work. This aimed at closely defining the
differing site water quantity and quality requirements, and
how they could be could be best met, while also meeting
project environmental management objectives. This work
demonstrated that almost all of the project’s water supply
requirements and environmental management targets
could be met by:
•
storing rain falling directly on the project’s processing
plant site (runoff from which potentially could be
contaminated from plant operations),
•
storing rain falling on the proposed tailings dam pond
and immediate surrounds (which would mix with
recycled process water)
•
storing water sourced from other small onsite sources
•
incorporating various levels of water treatment
•
maximising recycling of tailings water. That is, the early
estimate of ‘offsite’ water requirements (i.e. sources
from distant rivers, borefields etc.) of some 350 MLpa
could be reduced to almost nil.
As the main inputs to the site water balance model are
rainfall, which varies year-to-year, as well as within longer
time horizon patterns and trends, the modelling was
probabilistic i.e. it used statistical records to predict the
probability of a certain rainfall occurring in a particular year.
The output from many model ‘runs’ established confidence
levels of a particular outcome, such as water available from
the onsite sources in the median, or most likely, year (50th
percentile of the output values). This allowed testing of the
difference between median and wet and dry years, and the
planning implications for those years.
Overall, the modelling results showed that, with a modest
increase in site storage capacity, natural fluctuations in
input could be mitigated and the construction of significant
external ‘redundancy’ infrastructure could be avoided.
CASE STUDY:
WATER USE EFFICIENCY
This outcome had a triple bottom line benefit:
•
environmental
- no clearing of vegetation for
construction plus reduced energy use for pumping
•
social
- no groundwater water use in potential
competition with other users
•
economic
- no expensive infrastructure “insurance”
construction that may never be needed.
The headwaters of the Tambo River between the Currawong and Wilga deposits showing the steep topography
ENVIRONMENTAL IMPACT