bores being close to the pit (MB2, MB3, MB5S, MB5D and MB14) and Zone 2 bores being further from
the pit (MB8D and MB9).
The trigger values presented in DSITI (2015) are based on percentiles of historic observations
expressed as two trigger values rather than a single trigger level. DSITI’s (2015) approach was not
conventional. It was selected as “a compromise between the more traditional approach that employs a
comparison of the median (50th percentile) with a trigger based on the 80th percentile of a historical
reference data-set, and the control charting approach [...] that uses three control criteria lines”. In DSITI
(2015), Trigger 1 uses the more traditional approach, and it is a statistically robust method for detecting
gradual change over the medium term (i.e. 1 to 2 years). Trigger 2 permits the detection of event related
change over a relatively short term (i.e. several weeks depending on the sampling frequency).
Hydrobiology (2021) provided a review and update of the DSITI (2015) values, with additional data up
to September 2018.
6.3.2. Impact Assessment
The Heritage Minerals Project will ultimately result in improved environmental outcomes at the Mount
Morgan Mine through the excavation and historical ARD generating mine waste and redeposition of
treated tailings into the Sandstone Gully TSF, OCP and the Upper Mundic Gully TSF (if approved). This
will result in the removal of the source of ARD generating material from across the site reducing
recharge of and seepage from mine waste structures. This will reduce impacts from the Mount Morgan
Mine to the receiving environment including the Dee River in accordance with the State’s Rehabilitation
Plan (Unger et al, 2003) and Phase 2 Agreement.
Contaminated water seepage and runoff from the Mount Morgan Mine is currently managed by the
State via the seepage interception system. While this has reduced contamination loads, the system
cannot collect all contaminated water and water quality values in the Dee River remain adversely
affected. Mine affected water created from seepage or surface runoff is currently accumulated in
numerous facilities i.e. Shepherds Holding, No 2 Mill, Frog Hollow and Mundic West structures. Once
collected, the seepage and/or surface runoff is either left to evaporate or pumped back into the OCP,
with this location being the primary storage location for contaminated water.
The potential for the Upper Mundic Gully TSF to impact on groundwater values is considered unlikely
due to limited hydraulic conductivity and recharge of the underlying bedrock, referenced in Section 5.6,
and implementation of engineering controls. The TSF design has considered potential direct or indirect
releases to groundwater and mitigated through design undertaken by a RPEQ, installation of liners,
regular TSF inspections to be undertaken by the engineer of record and proposed groundwater
monitoring
The proposed installation of a liner on the upstream batter of the embankment to mitigate potential
seepage through the embankment. A geomembrane liner will be required as no suitable low
permeability clay material is found at the site. The liner bedding will be selectively borrowed from finer
mine waste, however as it is difficult to remove coarse particles, a more robust bituminous
geomembrane liner is proposed.
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Wulguru Technical Services Pty Ltd – Supporting Information to Amend an Environmental Authority
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