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Comité technique 215
The asbestos/lead area is close to the northern boundary of
the T4 Project area and the groundwater flow direction in
this part of the site is to the north;
At least 50 % of the asbestos and lead dust burial pits
would be expected to come into permanent or frequent
contact with groundwater following settlement induced by
preloading and subsequent T4 Project loads;
The long-term integrity of bags containing lead dust could
not be guaranteed (i.e. potential for existing bags to be
damaged, or become damaged due to loading and settlement,
or degradation over time); and
The lead dust is expected to be highly leachable when in
contact with groundwater.
4.3 Free Phase Hydrocarbon Area
Free-phase hydrocarbon impact, comprising Light Non-aqueous
Phase Liquid (LNAPL), was encountered in the Fill Aquifer at
two monitoring well locations in the southern part of the site.
The apparent thickness of floating product was found to be up
to 2 m. Fingerprint analysis of the free product found that the
sample was degraded mineral lubricating oil with trace amounts
of diesel. The analysis concluded that the oil was not a recent
release and may have been used in diesel engines.
The degree of impact generally diminished with distance
from the wells suggesting that the extent of free product was
relatively localised. Groundwater samples collected from the
Estuarine Aquifer wells recorded minor hydrocarbon impact in
the vicinity of free-phase impact.
4.4 Fines Disposal Facility
A 45 ha portion of the site known as the Fines Disposal Facility
(FDF) was used to receive dredged fine sediments during
various stages of construction of the existing coal terminal. The
dredged fines contain PAHs and heavy metals. A leachate
collection system generally maintains the groundwater level
below the contaminated sediments. Preload and site
development, however, will induce significant settlements
which are likely to impact on the leachate collection system.
This combined with the capping of the site is expected to result
in a rise water table level with the result that the lower 1.5 to
2.0 m of dredge spoil will end up below the water table in the
long term.
4.5 Manganese Dioxide Waste Area
This 25 ha former waste site contains electrolytic manganese
dioxide waste and localised hydrocarbon contamination (TRH
and PAH). The groundwater study identified that the main risk
associated with the manganese waste site would be vertical
infiltration of saline water during dredging due to the presence
of a thinner and more permeable clay aquitard below fill
materials compared to elsewhere on the T4 site. This presents a
risk of migration of contamination into the Estuarine Aquifer,
and increased groundwater effects on nearby surface water
bodies, in particular increased salinity levels in nearby surface
water ponds during dredging.
5 REMEDIATION
5.1 Review and Ranking of Available Options
A review of available remediation and management
technologies was undertaken prior to assessing the preferred
options for each of the contamination issues identified. Of the
many remediation technologies available, only well-established,
proven technologies were considered for the T4 Project.
Relevant regulatory guidelines and policies were also
considered when determining preferred options for remediation
and management.
Alternative and emerging remediation technologies were
also reviewed but discounted due to lack of experience and
uncertain effectiveness; these included electrochemical
remediation technologies (ECRT), supercritical fluid technology
(SCF) and nanotechnology, in particular the use of nano-scale
zero-valent iron (nZVI). Due to the site conditions preference
was given to in-situ technologies that do not require excavation
or removal of the contaminated soil and/or water to remediate
the area. Ex-situ technologies require the contaminated soil or
water to be removed from the ground for treatment, which can
either occur on- or off-site.
The remediation options for each contamination issue were
evaluated against the following attributes and weightings:
Technical Effectiveness (20%): the suitability of the
method to treat or manage the contaminant(s) of concern,
also considering geotechnical impacts (beneficial or
adverse);
Track Record in Australia (5%): whether or not the method
has been successfully used in Australia;
Availability (5%): the number of contractors who have the
expertise and equipment to implement the method; can
include international contractors who could bring the
technology into Australia;
Ease of Implementation (10%): consideration of site
constraints, regulatory hurdles and logistics;
Verification (5%): effectiveness of construction quality
control and ability to verify that specifications have been
achieved;
Sustainability (10%): the principles of environmentally
sustainable development and the use of resources, energy
inputs, waste generation, on-going management and
maintenance;
Stakeholder Acceptance (5%): the likely degree of
satisfaction of regulators, owner, neighbours and the
community with the remediation option;
Risk of off-site Migration (10%): effectiveness of the
method to inhibit contaminant transport;
Cost (20%): including trials, design, construction and
operation; and
Time to Implement (10%): trials, design and construction.
The attributes were each scored from 0 to 5 based on a
combination of quantitative and qualitative inputs, with zero
being ineffective, unavailable or very costly and 5 being the
best credible outcome. The total score was calculated as:
S
i
.W
i
(1)
where S
i
is the score for attribute i, and W
i
is the weighting for
attribute i. The result was an overall score out of 5.
Based on the ranking system described, the preferred
remediation options for each of the identified contamination
issues were selected, as summarised in Table 1. In each case the
three options with the highest score were identified so that
alternatives were not ruled out for the detailed design stage.
