January 2006 (PDF 2.9 MB) - Barrick Gold Corporation

Cowal Gold Project – Cyanide Management Plan
In summary, any limited seepage from the tailings storages is likely to have a negligible impact on
existing groundwater levels or quality and would migrate slowly towards the final void. Within some 30
to 40 years following Project closure, the tailings storages would be essentially de-saturated and
measurable seepage through the floor would cease.
A number of seepage control measures have been incorporated into the tailings storages, including:
• the pre-stripping of surficial soils beneath the embankment footprint;
• construction of a moisture-conditioned and compacted-low-permeability storage floor where
necessary, to achieve permeability criteria; and
• installation of an underdrainage and decant network.
As required by Consent Conditions 4.1/4.2(c)(i) and 5.2(a) the tailings storages will be constructed to
the requirements of DLWC, EPA, DMR and the NSW Dams Safety Committee (DSC). Further, the
floor of the tailings storages will be constructed and compacted to a permeability acceptable to the
DMR and EPA in consultation with DLWC, in accordance with Consent Condition 5.2(b).
In accordance with EPL 11912, the tailings storages and contained water storage facilities will have a
basal barrier or impermeable liner with an equivalent permeability of 1x10 -9 metres per second over a
thickness of 1 metre.
Following tailings deposition, supernatant water will drain to the central pond and decant towers. The
decant tower will be accessible via a causeway. An underdrainage pipe network will be installed to
facilitate drainage of the tailings mass. The bulk of the water from each tailings storage will, however,
drain from the surface of the tailings and collect in the centre of each storage. This water as well as
underdrainage water will be reclaimed and used within the processing plant. The decant system
(including access causeway) will be progressively raised during the development of the tailings
storages.
4.2.3.4 Tailings Storage Movement
Monitoring will be conducted for any movement of the tailings storages as described in the Monitoring
Programme for Detection of any Movement of Lake Protection Bund, Water Storage and Tailings
Structures and Pit/Void Walls, as follows:
• Visual assessments of the tailings structures will be undertaken routinely (i.e. weekly), following
review of surface and groundwater monitoring data and following seismic events to identify the
initial signs of movement.
• Survey assessment of the tailings structures will be routinely undertaken at six monthly intervals
or following visual assessments that indicate movement of a structure and/or following seismic
events to determine and quantify any movement of these structures.
HAL-02-07/1/25/CMP-01-Q.DOC 15 BARRICK