appendices - ntepa.nt.gov.au

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APPENDICES

SURFACE WATER IMPACT ASSESSMENT

APPENDIX C-5

Jervois Base Metal Project EIS Surface Water Impact Assessment

KGL Resources Pty Ltd 1348-01-C1, 18 September 2018

wrmwater.com.au 1348-01-C1| 18 September 2018 | Page 2

Report Title Jervois Base Metal Project EIS – Surface Water Impact Assessment

Client KGL Resources Pty Ltd 13 Bromley Street Alice Springs NT 0870

Report Number 1348-01-C1

Revision Number Report Date Report Author Reviewer

C1 18 September 2018 AN RC

For and on behalf of WRM Water & Environment Pty Ltd Level 9, 135 Wickham Tce, Spring Hill PO Box 10703 Brisbane Adelaide St Qld 4000 Tel 07 3225 0200

Rhys Cullen Associate / Principal Engineer

NOTE: This report has been prepared on the assumption that all information, data and reports provided to us by our client, on behalf of our client, or by third parties (e.g. government agencies) is complete and accurate and on the basis that such other assumptions we have identified (whether or not those assumptions have been identified in this advice) are correct. You must inform us if any of the assumptions are not complete or accurate. We retain ownership of all copyright in this report. Except where you obtain our prior written consent, this report may only be used by our client for the purpose for which it has been provided by us.

http://wrmwater.com.au/


Executive Summary

Overview

KGL Resources Pty Ltd (KGL) proposes to develop the Jervois Base Metal Project (the Project), a copper mine located approximately 270 km northeast of Alice Springs (383 km by road) in the Northern Territory (NT). The Project is located within Exploration Licence EL 25429 and several mineral leases held by Jinka Minerals Pty Ltd, a 100% owned subsidiary of KGL.

KGL is planning to mine copper and other base metals such as lead and zinc by both open cut and underground methods. The Project has a proposed mine life of 12 to 15 years, mining approximately 1.6 Mtpa Run of Mine (ROM) per annum, and producing approximately 200,000 tonnes of base metal concentrate per annum.

There is existing historical mine disturbance at the project including tailings storage dams, a waste rock dump, processing plant equipment, an open cut mining pit, numerous prospecting trenches, a ROM pad area and some ore stockpiles.

The modelling undertaken in this study demonstrates that with appropriate surface water management and mitigation measures in place, the potential impact of the Project on surface flows and water quality in the receiving waters downstream of the Jervois Mine will be insignificant.

Surface water management strategy

The proposed Jervois surface water management strategy will use a number of surface water management measures that will be implemented during construction, operational and post-closure periods.

For surface water management purposes, the surface water that is generated and/or managed at the Project is divided into five classes based on water quality:

• Undisturbed runoff: runoff from catchments unaffected by mining;

• Raw water (potable standard): raw water suitable for use in supplying the potable water treatment plant. Raw water (potable) standard will not have been in contact with any areas disturbed by mining, or any ore bodies. Raw water (potable standard) is typically sourced from Jervois Dam or the external borefield.

• Raw water (plant standard): water suitable for use in the raw water streams of the process plant. Raw water (plant standard) will have suitably low levels of TSS to prevent clogging of machinery nozzles but may have elevated levels of metalloids. Raw water (plant standard) is typically sourced from groundwater dewatered from the underground mining operations.

• Sediment laden water: sediment laden runoff from waste rock dumps. Sediment laden water is suitable for use as make-up process water in the plant, and for dust suppression. May be suitable for release to the environment dependant on long term water quality monitoring results.

• Mine affected water: runoff from areas where chemicals, contaminants or oxidised ore may be present. Includes runoff that collects from the process plant, ROM and product stockpiling areas, open cut mining pits and tailings storage facilities. Suitable for use as make up process water in the plant and for dust suppression. Unlikely to be suitable for release to the environment.

The key objectives of the Project’s water management system are:

• To protect environmental values of the receiving waters downstream of the Project during the operational period and post-closure; and

• To ensure that the Project has sufficient water available for operations during dry times.

The above objectives will be achieved by:



• Maintaining existing surface water drainage patterns where practical to do so;

• Managing water from different sources separately:

o Undisturbed runoff will be diverted around disturbed areas where practical;

o Mine affected water collected in-open cut pits, and in the process water dam will be managed using temporary in-pit sumps and re-used within the water management system;

o Sediment-laden runoff from the proposed waste rock dumps will be captured in dedicated sediment dams and re-used within the water management system;

o Raw water (plant standard) dewatered from the open cut pits and underground mines will be reused within the water management system.

• Using water collected on site as part of mining operations preferentially in order to reduce demand on external water sources. Water for mine operating purposes (excluding raw water demands) will be sourced preferentially as follows:

o Mine affected water;

o Sediment laden water;

o Raw water (plant standard), dewatered from the underground mines;

o Raw water (potable standard), sourced from Jervois Dam; and

o Raw water (potable standard) sourced from the external borefield.

The above water management objectives, when implemented through appropriate management plans, will mitigate the effects of the Project on natural surface water quantity and quality and flooding downstream of the mine site during operations and post-closure.

Water balance

The Project will initially be a net importer of water due to the predicted site demands exceeding groundwater inflows. Later in project life groundwater inflows increase and equal or exceed site demands, resulting in some accumulation of water on site.

Almost all of the direct rainfall and surface runoff inflows to the water management system are generated during the wet season between November and April. During the dry season between May and October, the majority of inflows to the water management system are generated from groundwater inflows to the underground mines. Groundwater seepage to the open cut pits at the project is predicted to be insignificant after evaporation from the pit surface (CloudGMS, 2018).

Water balance modelling has identified the following key surface water management infrastructure and measures that would be required as part of the Project:

• A new 180 ML process water dam to be constructed between the proposed process plant and the reward open cut pit;

• A new 10 ML underground dewatering dam adjacent to the process plant;

• Sediment dams to capture and manage runoff from waste rock dumps;

• Repairs and upgrades to the existing Jervois dam embankment and spillway to improve dam storage and safety;

The water balance modelling results indicate that, with the proposed water management infrastructure and measures in place, the proposed water management system will be robust and will have adequate storage capacity to manage surface water runoff and groundwater generated within the Project site for a wide range of possible climatic conditions, including extended wet and dry periods.



Flood impacts

The Project site is traversed by Unca Creek and its tributaries. The proposed Reward pit is located within the channel and floodplain of Unca Creek and would be affected by Unca Creek floodwaters. No other project infrastructure is affected by flooding.

It is proposed to construct a permanent diversion of Unca Creek around the Reward pit. The Unca Creek diversion will ensure that the Reward pit is protected from floodwater from the upstream catchment (including overflows from Jervois Dam) for events up to and including 0.1% annual exceedance probability (AEP), equivalent to 1,000 years average recurrence interval (ARI).

The final landform between the Reward pit and the creek diversion will ensure that the final void is protected from inundation for all flood events up to and including the Probable Maximum Flood (PMF) event. The Unca Creek diversion will remain in place as part of the final landform.

The proposed Jervois Dam upgrade will increase peak discharges, flood levels and velocities in Unca Creek downstream of the dam due to the increased spillway capacity. The predicted increases in flood levels and velocities are typically confined to the Unca Creek channel and do not affect any existing structures or property. The increased levels and velocities would be no greater than pre-dam levels and velocities, and therefore the impact is not predicted to change the morphological behaviour of Unca Creek.

The upgraded Jervois Dam will also result in an increased inundation area for the lake upstream of the dam. The increased inundation extent does not affect any existing structures or sensitive environmental or cultural heritage areas. The impact of the increase inundation area is considered insignificant. The mine closure plan for Jervois Dam could include the upgraded dam remaining in place or reduction in spillway level to the pre-mining level.

Impacts on Unca Creek streamflow

The proposed upgrade to Jervois Dam will alter the streamflow regime in Unca Creek downstream of the dam, with reduced frequency of spill events, but increased maximum spill rates:

• Under existing conditions, Jervois Dam is predicted to overflow via the spillway on approximately 0.8% of all days. That is, there is no flow over the spillway 99.2 % of the time;

• Under the post mine closure scenario (upgraded dam and no site demands), the dam is predicted to overflow about 0.15 % of the time. That is, there would be no flow over the spillway for 99.85 % of the time.

The existing dam on average only overflows in every fourth year. The upgraded dam is predicted to overflow every 9 years under the post-mine closure scenario.

It should be noted that the relative impact of the dam on Unca Creek streamflows will be reduced downstream of the Project, as the catchment of Unca Creek almost doubles at the confluence with Unca Creek tributary east of Lucy Creek Access Road.

Impacts on water quality

The Project has the potential to impact on water quality in Unca Creek and its tributaries due to controlled and uncontrolled releases of sediment laden water.

The results of the water balance model show that no uncontrolled or controlled releases of mine affected water are predicted from the process water dam in any of the water balance model simulations. No dewatered groundwater will be released to the environment.

Runoff from the waste rock dump sediment dams will be managed as follows:

• During the first 4 years of project life, when groundwater inflows to the underground mine are low, runoff captured in the waste rock sediment dams will be pumped back to the process water dam.



• Surface runoff and seepage from waste rock dumps that collects in the sediment dams would be monitored for water quality parameters including, but not limited to pH, EC, major anions (sulfate, chloride and alkalinity), major cations (sodium, calcium, magnesium and potassium), TDS and a broad suite of soluble metals/metalloids;

• The sediment dam monitoring would be used to validate the anticipated quality of water runoff reporting to sediment dams. Initially, the sediment dam monitoring would occur on an event basis to demonstrate the water quality of stored waters is consistent with the relevant water quality objectives to allow releases from sediment dams to occur if required.

• Subject to demonstrating the water quality objectives can be met, the frequency of monitoring and suite of parameters for the sediment dam monitoring would be reviewed and updated accordingly (e.g. to occur only when releases occur).

• It is anticipated that by EOY4 of mine life, sufficient water quality monitoring data would be available to determine if runoff and seepage from the waste rock dumps is suitable for release from the sediment dams following runoff events. If this is the case, then runoff captured in the waste rock sediment dams would no longer be pumped back to the process water dam and would be released to the receiving environment within 5 days of a runoff event occurring (as per best practice sediment dam operation).

• If water quality monitoring data indicates that waste rock dump runoff is not suitable for release, the sediment dams will continue to be pumped back to the process water dam beyond EOY4.

Uncontrolled releases (spills) from the waste rock sediment dams may occur in the first four years of mining if the design criteria of the sediment dams is exceeded (i.e. a rainfall event greater than the 10% AEP 24-hour storm occurs whilst the waste rock dump catchments are saturated). The water balance model indicates that there is approximately a 10% chance of uncontrolled releases from the waste rock sediment dams in the first four years of Project life.

The sediment dams are sized to capture all runoff from the dumps during a 10% AEP 24-hour rainfall event. For an event of this magnitude, the flow in the receiving watercourses would dilute any uncontrolled releases from the sediment dams before reaching the downstream boundary of the Project.

Impacts of final voids on surface water

The final landform hydraulic modelling has demonstrated that the final voids will be protected from flooding from Unca Creek and its tributaries for all events up to and including the PMF.

Therefore, the only water that collects in the final voids will be surface water runoff from the pit catchments. This runoff will collect in the base of the pits and evaporate over time. The final landform for the Project will ensure that the remnant surface water catchments that drain into the final voids are limited to the voids themselves and therefore the stored water cannot overflow to impact on surface water.

Surface water monitoring

Monitoring of surface water quality will be ongoing as part of the Project, both for background water quality locations (undisturbed by mining), the surface water storages proposed as part of the project, and in receiving environments downstream of the Project area.

The proposed storages at the Project (process water dam, Jervois Dam, underground dewatering dam and waste rock sediment dams) will be monitored at least quarterly (and daily during or following runoff events).

Background and receiving water monitoring will continue to take place following runoff events at the existing monitoring locations.



Contents

1 Introduction _________________________________________________ 15 1.1 Background ____________________________________________________ 15 1.2 Project summary ________________________________________________ 16 1.3 Report structure ________________________________________________ 16

2 Regulatory framework _________________________________________ 18 2.1 Overview ______________________________________________________ 18 2.2 Commonwealth legislation _______________________________________ 18

2.2.1 State legislation EPBC Act __________________________________ 18 2.3 State legislation ________________________________________________ 18

2.3.1 Environmental Assessment Act ______________________________ 18 2.3.2 Water Act ________________________________________________ 18 2.3.3 Terms of References for EIS – surface water ___________________ 18

3 Existing environment __________________________________________ 23 3.1 Regional drainage characteristics __________________________________ 23 3.2 Local drainage characteristics ____________________________________ 25

3.2.1 General __________________________________________________ 25 3.2.2 Jervois Dam ______________________________________________ 25 3.2.3 Historical mining activities __________________________________ 25

3.3 Climatic data ___________________________________________________ 34 3.3.1 Overview ________________________________________________ 34 3.3.2 Rainfall __________________________________________________ 34 3.3.3 Evaporation ______________________________________________ 34

3.4 Streamflow ____________________________________________________ 36 3.4.1 Overview ________________________________________________ 36 3.4.2 Jervois Dam stage-storage relationship _______________________ 36 3.4.3 Existing streamflow characteristics __________________________ 36

3.5 Aquatic ecosystems _____________________________________________ 38 3.6 Geology _______________________________________________________ 38 3.7 Groundwater ___________________________________________________ 38 3.8 Groundwater extraction licences __________________________________ 38 3.9 Surface water quality ____________________________________________ 39

3.9.1 Water quality data ________________________________________ 39 3.9.2 Grouped water quality data _________________________________ 39 3.9.3 Summary of water quality characteristics _____________________ 40

4 Environmental values and water quality objectives ___________________ 46 4.1 Environmental values ____________________________________________ 46 4.2 Water quality objectives _________________________________________ 46



4.2.1 Adopted water quality objectives ____________________________ 46 4.2.2 Comparison of WQOs against observed water quality ____________ 47

5 Project description ____________________________________________ 49 5.1 Mining areas and operations ______________________________________ 49 5.2 Proposed infrastructure __________________________________________ 49

5.2.1 Reward infrastructure ______________________________________ 49 5.2.2 Bellbird infrastructure _____________________________________ 49 5.2.3 Rockface infrastructure ____________________________________ 49 5.2.4 Jervois Dam ______________________________________________ 51 5.2.5 Process plant _____________________________________________ 51 5.2.6 Tailings storage facility ____________________________________ 51 5.2.7 Accommodation camp and administration _____________________ 51

5.3 Project staging _________________________________________________ 51 6 Proposed water management strategy and infrastructure ______________ 53

6.1 Overview ______________________________________________________ 53 6.2 Surface water types _____________________________________________ 53 6.3 Water management principles ____________________________________ 53 6.4 Contaminant source study ________________________________________ 54

6.4.1 Potential contaminant sources ______________________________ 54 6.4.2 Contaminant concentrations in site runoff ____________________ 54

6.5 Water management system infrastructure __________________________ 55 6.5.1 Unca Creek diversion ______________________________________ 55 6.5.2 Surface water storages _____________________________________ 59 6.5.3 Clean and dirty water diversion drains ________________________ 60 6.5.4 Tailings storage facility ____________________________________ 61 6.5.5 External borefields ________________________________________ 61 6.5.6 Haul and access road crossings ______________________________ 61 6.5.7 Potable water and wastewater treatment _____________________ 61

6.6 Groundwater inflows ____________________________________________ 61 6.6.1 Open cut mining pit dewatering _____________________________ 61 6.6.2 Underground mine dewatering ______________________________ 61 6.6.3 Sensitivity of predicted groundwater inflows __________________ 62

6.7 Waste rock dump runoff and sediment dams ________________________ 62 6.8 Site water demands _____________________________________________ 63

6.8.1 Potable water demands ____________________________________ 63 6.8.2 Process plant demands _____________________________________ 63 6.8.3 Dust suppression __________________________________________ 64 6.8.4 Underground mining equipment demands _____________________ 64

6.9 Management of existing mine disturbance areas _____________________ 65



6.9.1 Process plant and ROM pad _________________________________ 65 6.9.2 Tailing dams ______________________________________________ 65 6.9.3 Waste rock dump __________________________________________ 65 6.9.4 Existing Green Parrot open cut pit ___________________________ 65

7 Water balance modelling _______________________________________ 66 7.1 Overview ______________________________________________________ 66 7.2 Interpretation of results _________________________________________ 66 7.3 Water balance model results ______________________________________ 67

7.3.1 Overall water balance _____________________________________ 67 7.3.2 Mine site storage inventory _________________________________ 68 7.3.3 External water demand ____________________________________ 74 7.3.4 Uncontrolled releases (spillway overflows) ____________________ 75

7.4 Final void behaviour _____________________________________________ 76 8 Flood modelling assessment _____________________________________ 79

8.1 Overview ______________________________________________________ 79 8.2 Existing conditions flooding _______________________________________ 79 8.3 Operational conditions flooding ___________________________________ 86

8.3.1 Overview ________________________________________________ 86 8.3.2 Operational conditions peak flood levels, depths and extents ____ 86 8.3.3 Operational conditions flood impacts _________________________ 86

8.4 Unca Creek diversion ____________________________________________ 97 8.4.1 Overview ________________________________________________ 97 8.4.2 Diversion channel configuration _____________________________ 97 8.4.3 Flood assessment __________________________________________ 97

8.5 Final landform flooding assessment _______________________________ 102 9 Surface water monitoring ______________________________________ 105

9.1 Overview _____________________________________________________ 105 9.2 Surface water storages _________________________________________ 105 9.3 Background sites and receiving waters ____________________________ 107

10 Potential impacts and proposed mitigation measures ________________ 108 10.1 Changes to streamflow in Unca Creek _____________________________ 108

10.1.1 Potential impacts ________________________________________ 108 10.1.2 Proposed mitigation ______________________________________ 109

10.2 Increase in Jervois Dam lake extent _______________________________ 109 10.2.1 Potential impacts ________________________________________ 109 10.2.2 Proposed mitigation ______________________________________ 109

10.3 Impacts on flooding ____________________________________________ 111 10.3.1 Potential impacts ________________________________________ 111 10.3.2 Proposed mitigation ______________________________________ 112



10.4 Impacts on water quality ________________________________________ 112 10.4.1 Potential impacts ________________________________________ 112 10.4.2 Proposed mitigation ______________________________________ 112

10.5 Impact of final voids on surface water _____________________________ 113 10.5.1 Potential impacts ________________________________________ 113 10.5.2 Proposed mitigation ______________________________________ 113

11 References _________________________________________________ 114 – Mining schedules and plans _____________________________ 115 – Mine water balance model configuration __________________ 126 – Hydrological and hydraulic model development _____________ 145



List of Figures

Figure 1.1 – Location of the Project _____________________________________________ 15 Figure 1.2 – Conceptual layout of the Project ____________________________________ 17 Figure 3.1 – Hay River basin drainage network ____________________________________ 24 Figure 3.2 – Local drainage network in the vicinity of the Project ____________________ 27 Figure 3.3 – Photo A – Jervois Dam water surface, looking west _____________________ 28 Figure 3.4 – Photo B – downstream of Jervois Dam spillway _________________________ 28 Figure 3.5 – Photo C – Unca Creek channel at the proposed Reward Pit location ________ 29 Figure 3.6 – Photo D – Unca Creek channel at the proposed Reward Pit location ________ 29 Figure 3.7 – Photo E – Unca Creek channel, with monitoring site JSW10 _______________ 30 Figure 3.8 – Photo F – Unca Creek tributary channel, with monitoring site JSW07 ______ 30 Figure 3.9 – Photo G – Unca Creek tributary channel, with monitoring site JSW05 ______ 31 Figure 3.10 – Photo H – Unca Creek tributary channel ______________________________ 31 Figure 3.11 – Photo I – existing Green Parrot open cut pit __________________________ 32 Figure 3.12 – Photo J – existing processing plant taken from ROM pad ________________ 32 Figure 3.13 – Photo K – old tailings storage dam ___________________________________ 33 Figure 3.14 – Photo L – old tailings storage dam ___________________________________ 33 Figure 3.15 – Distribution of Patch Point average monthly rainfall and evaporation _____ 35 Figure 3.16 – Adopted Jervois Dam stage-storage relationship _______________________ 36 Figure 3.17 – Recorded water levels in Jervois Dam (1972 to 2010) ___________________ 37 Figure 3.18 – Recorded volumes in Jervois Dam (1972 to 2010) ______________________ 37 Figure 3.19 – Locations of baseline surface water quality monitoring sites ____________ 41 Figure 5.1 – Jervois project layout ______________________________________________ 50 Figure 6.1 – Proposed water management system (WMS) lay out for the Reward

mining operations __________________________________________________ 56 Figure 6.2 – Proposed water management system (WMS) layout for the Bellbird and

Rockface mining operations _________________________________________ 57 Figure 6.3 – Water management system schematic ________________________________ 58 Figure 6.4 – Repaired Jervois Dam stage-storage relationship _______________________ 60 Figure 6.5 – Predicted groundwater inflows to underground mines ___________________ 62 Figure 7.1 – Process Water Dam stored inventory __________________________________ 69 Figure 7.2 – Jervois Dam stored inventory ________________________________________ 69 Figure 7.3 – Reward Open Cut Pit stored inventory ________________________________ 70 Figure 7.4 – Bellbird South Open Cut Pit stored inventory __________________________ 71 Figure 7.5 – Bellbird North Open Cut Pit stored inventory __________________________ 71 Figure 7.6 – Rockface Underground Mine stored inventory __________________________ 72 Figure 7.7 – Reward Underground Mine stored inventory ___________________________ 72 Figure 7.8 – Bellbird Underground Mine stored inventory ___________________________ 73 Figure 7.9 – Existing Marshall Reward pit stored inventory __________________________ 73



Figure 7.10 – Annual external water requirements_________________________________ 74 Figure 7.11 – Final void water levels – Reward Void ________________________________ 77 Figure 7.12 – Final void water levels – Bellbird South Void __________________________ 77 Figure 7.13 – Final void water levels – Bellbird North Void __________________________ 78 Figure 8.1 – Peak flood depths and extents, existing conditions, 10% AEP (10 year

ARI) event ________________________________________________________ 80 Figure 8.2 – Peak flood depths and extents across the entire Project area, existing

conditions, 1% AEP (100 year ARI) event _______________________________ 81 Figure 8.3 – Peak flood depths and extents near the Reward Pit and Process Plant

area, existing conditions, 1% AEP (100 year ARI) event ___________________ 82 Figure 8.4 – Peak flood velocities across the entire Project area, existing conditions,

10% AEP (10 year ARI) event _________________________________________ 83 Figure 8.5 – Peak flood velocities across the entire Project area, existing conditions,

1% AEP (100 year ARI) event _________________________________________ 84 Figure 8.6 – Peak flood velocities near the Reward Pit and Process Plant area,

existing conditions, 1% AEP (100 year ARI) event ________________________ 85 Figure 8.7 – Peak flood depths and extents across the entire Project area,

operational conditions, 10% AEP (10 year ARI) event _____________________ 87 Figure 8.8 – Peak flood depths and extents across the entire Project area,

operational conditions, 1% AEP (100 year ARI) event _____________________ 88 Figure 8.9 – Peak flood depths and extents near the Reward Pit and Process Plant

area, existing conditions, 1% AEP (100 year ARI) event ___________________ 89 Figure 8.10 – Peak flood depths and extents across the entire Project area,

operational conditions, 10% AEP (10 year ARI) event _____________________ 90 Figure 8.11 – Peak flood depths and extents across the entire Project area,

operational conditions, 1% AEP (100 year ARI) event _____________________ 91 Figure 8.12 – Peak flood depths and extents near the Reward Pit and Process Plant

area, existing conditions, 1% AEP (100 year ARI) event ___________________ 92 Figure 8.13 – Predicted increases in peak flood levels under operational conditions,

10% AEP (10 year ARI) event _________________________________________ 93 Figure 8.14 – Predicted increases in peak flood levels under operational conditions,

1% AEP (100 year ARI) event _________________________________________ 94 Figure 8.15 – Predicted increases in peak flood velocities under operational

conditions, 10% AEP (10 year ARI) event _______________________________ 95 Figure 8.16 – Predicted increases in peak flood velocities under operational

conditions, 1% AEP (100 year ARI) event _______________________________ 96 Figure 8.17 – Proposed Unca Creek Diversion, with 0.1% AEP flood extents under

existing and operational conditions ___________________________________ 98 Figure 8.18 – Longitudinal profile along the proposed diversion alignment ____________ 99 Figure 8.19 – Comparison of channel cross sections at four locations along the

proposed Unca Creek Diversion (looking downstream) __________________ 100 Figure 8.20 – Existing conditions peak flood velocities along the existing Unca Creek

alignment, 10%, 1% and 0.1% AEP events ______________________________ 101 Figure 8.21 – Operational conditions peak flood velocities along the diverted Unca

Creek alignment, 10%, 1% and 0.1% AEP events ________________________ 101 Figure 8.22 – Proposed final landform configuration, with PMF event peak flood

levels, depths and extents__________________________________________ 103



Figure 8.23 – Predicted PMF peak flood levels along the proposed Western Bund alignment (west to east) ___________________________________________ 104

Figure 8.24 – Predicted PMF peak flood levels along the proposed Eastern Bund alignment (north to south) _________________________________________ 104

Figure 9.1 – Surface water monitoring program __________________________________ 106 Figure 10.1 – Impact of upgraded Jervois Dam on Unca Creek flows _________________ 109 Figure 10.2 – Impact of upgraded Jervois Dam on inundation extent at full supply

level ____________________________________________________________ 110 Figure 10.3 – Impact of upgraded Jervois Dam on inundation frequency ______________ 111

Figure A.1 – Open cut mining at the Reward Pit at the end of year 1 (EOY1) __________ 116 Figure A.2 – Open cut mining at the Reward Pit at the end of year 5 (EOY5) __________ 117 Figure A.3 – Underground mining at the Reward Pit at the end of year 4 (EOY4) ______ 118 Figure A.4 – Underground mining at the Reward Pit at the end of year 10 (EOY10) ____ 119 Figure A.5 – Open cut mining at the Bellbird Pit at the end of year 5 (EOY5) _________ 120 Figure A.6 – Open cut mining at the Bellbird Pit at the end of year 5 (EOY8) _________ 121 Figure A.7 – Underground mining at the Bellbird Pit at the end of year 7 (EOY10) _____ 122 Figure A.8 – Underground mining at the Bellbird Pit at the end of year 10 (EOY10) ____ 123 Figure A.9 – Underground mining at the Rockface Pit at the end of year 1 (EOY1) _____ 124 Figure A.10 – Underground mining at the Rockface Pit at the end of year 7 (EOY7) ____ 125 Figure B.1 – TUFLOW model configuration for the existing Jervois Dam spillway_______ 128 Figure B.2 – Catchments and landuses at the Reward Pit, from EOY0 to EOY10 ________ 133 Figure B.3 – Catchments and landuses at the Bellbird Pit, from EOY4 to EOY10 _______ 134 Figure B.4 – Water management system schematic _______________________________ 135 Figure B.5 – AWBM model (Boughton, 2010) _____________________________________ 139 Figure B.6 – Comparison of recorded and simulated volumes in Jervois Dam from

1977 to 2010 _____________________________________________________ 141 Figure C.1 – URBS model configuration _________________________________________ 147 Figure C.2 – Adopted stage-discharge relationships for the Jervois Dam spillway

under existing and operational conditions _____________________________ 149 Figure C.3 – Distribution of 10% AEP design peak discharges in Unca Creek upstream

of the Project (URBS subcatchment 43), existing conditions _____________ 152 Figure C.4 – Distribution of 1% AEP design peak discharges in Unca Creek upstream

of the Project (URBS subcatchment 43), existing conditions _____________ 153 Figure C.5 – Existing conditions TUFLOW model configuration ______________________ 156 Figure C.6 – Operational conditions TUFLOW model configuration __________________ 157 Figure C.7 – Final landform TUFLOW model configuration _________________________ 158 Figure C.8 – TUFLOW model configuration for the existing Jervois Dam spillway ______ 159



List of Tables

Table 2.1 – Final Terms of Reference (TOR) for the Project – surface water ___________ 19 Table 3.1 – Long-term Patch Point average monthly rainfall and evaporation __________ 35 Table 3.2 – Statistical summary of daily maximum recorded volumes in Jervois Dam ____ 38 Table 3.3 – Water quality data for the watercourses across the Project area __________ 42 Table 3.4 – Grouped water quality data for undisturbed areas in Unca Creek and the

Unca Creek Tributary _______________________________________________ 45 Table 4.1 – Adopted surface water quality objectives (WQOs) for the Project, and

comparison with observed water quality data __________________________ 48 Table 5.1 – Adopted mine stages _______________________________________________ 52 Table 6.1 – Contaminant sources and destinations of runoff _________________________ 54 Table 6.2 – Surface water storages ______________________________________________ 59 Table 6.3 – Dust suppression demand ____________________________________________ 64 Table 6.4 – Underground mining demand ________________________________________ 65 Table 7.1 – Annual site water balance (average annual volumes) ____________________ 68 Table 7.2 – Annual external water requirements __________________________________ 75 Table 7.3 – Annual total volume of overflows from the sediment dams _______________ 76 Table 8.1 – Proposed Unca Creek Diversion channel characteristics __________________ 99 Table 9.1 – Surface water storage monitoring parameters and frequencies ___________ 105 Table 9.2 – Background and receiving water monitoring locations ___________________ 107

Table B.1 – Long-term average monthly rainfall and evaporation ___________________ 128 Table B.2 – Simulated Inflows and Outflows to Mine Water Management System ______ 129 Table B.3 – Adopted mine stages ______________________________________________ 130 Table B.4 – Storage catchment areas ___________________________________________ 132 Table B.5 – Water management system operating rules ___________________________ 136 Table B.6 – Adopted AWBM parameters for various catchment types ________________ 140 Table B.7 – Dust suppression demand __________________________________________ 142 Table B.8 – Underground mining demand _______________________________________ 142 Table B.9 – Predicted groundwater inflows underground mines _____________________ 143 Table B.10 – Process Water Dam (PWD) key details _______________________________ 144 Table B.11– Sediment dam sizing ______________________________________________ 144 Table C.1 – Adopted URBS model subcatchment areas ____________________________ 148 Table C.2 – Adopted URBS model catchment and routing parameters ________________ 148 Table C.3 – Adopted Jervois Dam spillway characteristics _________________________ 149 Table C.4 – Adopted design rainfall depths ______________________________________ 151 Table C.5 – Predicted design peak discharges and critical storm durations in Unca

Creek upstream of the Project (URBS Subcatchment 43) ________________ 152



1 Introduction

1.1 BACKGROUND KGL Resources Pty Ltd (KGL) proposes to develop the Jervois Base Metal Project (the Project), a copper mine located approximately 270 km northeast of Alice Springs (383 km by road) in the Northern Territory (NT). Road access to the Project from Alice Springs is via the Stuart Highway and Plenty Highway. The Project is located within Exploration Licence EL 25429 and several Mineral Leases held by Jinka Minerals Pty Ltd, a 100% owned subsidiary of KGL. Figure 1.1 shows the locations of the Project.

KGL is planning to mine copper and other base metals such as lead and zinc by both open cut and underground methods. The Project has a proposed mine life of 12 to 15 years, mining approximately 1.6 Mtpa Run of Mine (ROM) per annum, and producing approximately 200,000 tonnes of base metal concentrate per annum.

KGL engaged Nitro Solutions Pty Ltd (Nitro Solutions) to prepare an Environmental Impact Statement (EIS) for the Project. A Notice of Intent (NOI) and associated documents were submitted to the Northern Territory Environment Protection Authority (NT EPA) in January 2017. As a result, the NT EPA have issued a Terms of Reference (TOR) for the Project.

As part of the Project EIS, Nitro Solutions (on behalf of KGL) requested WRM Water & Environment Pty Ltd (WRM) to undertake a surface water assessment for the Project. This report presents the methodology and results of investigations undertaken to characterise surface water quality and quantity on the Project site, the surface water impacts of the Project as well as proposed mitigation measures.

Figure 1.1 – Location of the Project



1.2 PROJECT SUMMARY The Project mineralised zones include Marshall, Reward, Bellbird, Green Parrot, Cox’s Find and Rockface. KGL will focus their mining activities on the Reward, Bellbird and Rockface deposits. KGL intend to selectively mine the deposits in an open pit scenario, followed by a switch to underground extraction.

There is existing historical mine disturbance at the project including tailings storage dams, a waste rock dump, processing plant equipment, an open cut mining pit, numerous prospecting trenches, a ROM pad area and some ore stockpiles.

Mine infrastructure will include pits, waste rock landforms, tailings storage facilities, topsoil stockpiles, haul roads, heavy vehicle parking areas, ROM pads and fuel storage areas. The processing plant will include associated water tanks, workshops, fuel facilities, concentrate load out facility, mobile equipment, power plant, air and water supply facilities and storage areas. Other infrastructure associated with the project will include laydown areas, production and monitoring bores, a magazine and explosives store, an upgraded accommodation camp, administration buildings, new sediment catchment dams, access and haul roads, monitoring and supply bores, power generation and supply facilities, workshops, hardstands and laydown areas. Proposed infrastructure will be located over previously disturbed mine infrastructure areas wherever feasible as indicated in Figure 1.2.

1.3 REPORT STRUCTURE This report is structures as follows:

• Section 2 presents the relevant regulatory framework for the Project, including the Terms of Reference (ToR);

• Section 3 describes the existing environment characteristics;

• Section 4 describes the environmental values and water quality objectives;

• Section 5 describes the location and extent of infrastructure for the Project;

• Section 6 describes the proposed water management strategy and infrastructure for the Project;

• Section 7 provides a summary of the water balance results for the mine water management system;

• Section 8 describes the outcomes from the hydrological and hydraulic modelling assessment;

• Section 9 describes the proposed surface water monitoring program for the Project;

• Section 10 describes the outcomes from the surface water impact assessment as well as the proposed measures to mitigate the impacts;

• Section 11 gives a list of references;

• Appendix A presents the mine stage plans;

• Appendix B describes the mine water balance model development; and

• Appendix C describes the hydrological and hydraulic model development.



Figure 1.2 – Conceptual layout of the Project



2 Regulatory framework

2.1 OVERVIEW This section describes the regulatory framework (legislation, policies and standards) at Commonwealth and State level that would apply to surface water management for the Project.

2.2 COMMONWEALTH LEGISLATION

2.2.1 State legislation EPBC Act

The Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act) is the Australian Government’s central piece of environmental legislation. It outlines the requirements relating to the management and protection of matters of national environmental significance (MNES). On 27 February 2014, advice was received from the Australian Government Department of the Environment and Energy (DoE) that the Project was not considered to be a Controlled Action and did not require assessment or approval under the EPBC Act.

2.3 STATE LEGISLATION

2.3.1 Environmental Assessment Act

The Environmental Assessment Act 1982 (EA Act) provides for “the assessment of the environmental effects of development proposals and for the protection of the environment”. On 25 February 2014, the NT EPA decided that the project required assessment under the EA Act at the level of Environmental Impact Statement (EIS).

2.3.2 Water Act

The Water Act (Water Act) provides for the investigation, allocation, use, control, protection and management of surface water and groundwater resources, as well as processes for licensing these activities. The Water Act also provides for the protection and use of water resources for specified purposes such as recreational, social, agricultural, environmental and cultural uses.

Under the Water Act, mining activities or another activity for a purpose ancillary to that mining activity (including the use of water as drinking water) are exempt from a number of provisions in the Water Act. This includes, and is not limited to, the use of surface water and groundwater, as well as the construction of works to allow for the use of water.

The Water Act also regulates the disposal of waste into water. Waste is defined any solids, liquids or gas, which, if added to the water, may pollute the water.

2.3.3 Terms of References for EIS – surface water

The NT Environmental Protection Agency (EPA) requires an EIS be prepared for the Project under the EA Act. As a result, the NT EPA have issued a Terms of Reference (TOR) for the Project in August 2017. The site-specific Terms of Reference (TOR) seek information corresponding to the Project’s assessment requirements under the EA Act.

This surface water assessment, which forms part of the Project EIS, addresses the TORs concerning surface water. Table 2.1 lists the elements of the TOR relevant to this assessment and the sections of this report where those TORs are addressed.



Table 2.1 – Final Terms of Reference (TOR) for the Project – surface water

Requirement Report section

2.2 Project Components

2.2.7 Water

Describe water use, including:

• Project water balance and account. Predictions should include rainfall over wet, dry and average years;

• water demand requirements for each aspect of the Project (including dust suppression, drinking water, ablutions and sewage treatment, mine water, processing circuit and any other uses);

• water supply source(s);

• diversion of surface waters;

• pit dewatering requirements;

• water efficiency and recycling; and

Please refer to the Northern Territory Department of Primary Industry and Resources Template for the Preparation of a Mining Management Plan (Section 6 – Water Management)

Section 6 and 7

3.1 Physical environment

The description of the physical environment must include:

• weather and climate (e.g. rainfall patterns [magnitude and seasonality], temperature, humidity, wind, climate extremes, and any seasonal conditions [e.g. floods or dust storms], which may influence the operation and/or rehabilitation, etc.)

Section 3

• regional and significant topography and geomorphology Section 3

• regional geology (e.g. major units, geotechnical surveys, seismic stability, significant geological properties that may influence stability, occupational health and safety, etc.)

Section 3

• regional geology (e.g. major units, geotechnical surveys, seismic stability, significant geological properties that may influence stability, occupational health and safety, etc.)

Section 3

• soil types and land unit(s), including details of any limiting properties of soil and substrate types (e.g. susceptibility to erosion, waterlogging) in the Project footprint

Section 3

• surface water, including:

o major and minor drainage lines (permanent and ephemeral)

o catchment boundaries

o surface water flow directions and rates

o water reservoirs (natural and artificial)

o wetlands

o areas of periodic inundation

Section 3




o beneficial uses

o surface water quality, including temporal variations

• groundwater aquifers and hydrogeological properties, including:

o surface connections via springs or recharge zones

o local and regional aquifers

o depth to water tables, including temporal variation

Section 3

4.1 Identified preliminary environmental factors

4.1.4 Hydrological processes

4.1.4.1 Relevant activities

The EIS should describe proposed activities that may have a significant impact on and/or pose a risk to hydrological processes such as activities that result in changes to surface hydrology and water extraction.

Section 10

4.1.4.2 Potential impacts and risks

Describe potential impacts and risks from changes to hydrological processes including impacts on the environment and other water users.

The EIS should describe:

• water demand requirements of the Project (a water balance and account)

• water supply source(s), volumes and sustainability

• proposed changes to the movement of surface waters

• other water uses including groundwater dependent ecosystems and the environment.

Section 10

4.1.4.3 Mitigation and monitoring

The EIS should describe proposed management of water for the Project for all mine-life stages and seasons including post mining, according to its source, quality, volume, end use or other parameters, including (but not limited to) measures to:

• safeguard surface and groundwater resources and their environmental values, including options for minimising water use

• ensure the protection and resilience of water dependent ecosystems.

Section 9 and 10

4.1.4.4 Relevant policy and guidelines

Australian and New Zealand Guidelines for Fresh and Marine Water Quality Section 4

4.1.5 Inland waters environmental quality

4.1.5.1 Relevant activities

The EIS should describe proposed activities that may have a significant impact on and/or pose a risk to inland waters environmental quality. This includes activities with the potential to contaminate water with chemicals, mine waste and sediment, and that result in changes to surface water hydrology.

Section 10




4.1.5.2 Potential impacts and risks Section 7 and Section 10

Describe potential impacts and risks to inland waters environmental quality and sensitive receptors.

The EIS should include a conceptual site model describing potential sources, pathways, receptors, and fate of any potentially contaminated waters from the Project. The model should be of sufficient detail for the general reader to understand the source(s) of potential contaminants, the mechanism(s) of their release, the pathway(s) for transport, and the potential for human and ecological exposure to these potential contaminants. The minimum data required to support the model should include, but should not be limited to:

• relevant laboratory and field testing to characterise the potential physicochemical properties of mine products and infrastructure (e.g. stockpiles, etc.)

By others (EGI, 2018)

• material volume and mass of potential contaminant sources By others (EGI, 2018)

• hydrogeological characterisation (e.g. groundwater occurrence, direction and rate of flow, etc.)

By others (CloudGMS, 2018)

• hydrologic characterisation (e.g. surface water flow, seasonality etc.) Section 3

• baseline water quality (i.e., major cations and anions, metals, metalloids, acidity/alkalinity, etc.) of receiving waters

Section 3

• biological receptors and their habitats Section 3

• other complementary technical studies, at an appropriate temporal and spatial scale, used to develop the model, such as:

o geology

o hydrology

o hydrogeology

o geochemistry

o biology

o meteorology

o engineering/geotechnical.

By others: CloudGMS (2018), EGI (2018), Low Ecological

4.1.5.3 Mitigation and monitoring

The EIS should provide a draft Water Management Plan (WMP) prepared by a suitably qualified expert. All mitigation measures in the WMP should be adequately detailed to demonstrate best practicable management and that environmental values of receiving waters will be maintained. The WMP should include, but not be limited to:

WRM (2018a)

• proposed management to contain contaminants onsite and details of contingency measures that will be implemented in the event of a spill or leak of chemicals that could impact on downstream water quality




• management of various categories of water (e.g. ‘clean’, ‘dirty’ and ‘contaminated’ -definitions can be provided in the draft EIS) including water quality thresholds triggering management actions

• management of chemicals and hydrocarbons

• management of tailings and associated process water during operations and post closure

• management of problematic waste rock during operations and post-closure

• non-mineral waste management strategies, including reduction, re-use, recycling, storage, transport and disposal of waste

• management of domestic wastewater and sewage

• management of process waters

• management of high/extreme rainfall events including Probable Maximum Precipitation and provisions for extreme rainfall and flood events in the management of tailings and waste rock, including erosion protection, management of seepage including sub-drainage and collection sumps

• management of erosion and sedimentation

• construction quality control processes

• measures to avoid the exposure of sensitive biological receptors to contaminants or water of a poor quality which may be harmful

• measures to ensure treatment / neutralisation occurs of hazardous materials to identified safe levels, before any controlled environmental release is considered

The WMP should include monitoring programs that detail relevant water quality target values based on appropriate guidelines and/or standards and ideally be based on local ambient conditions. The monitoring programs should include:

• methods to monitor the impacts of the Project on surface and groundwater quality and quantity during mine operations and beyond mine closure

• monitoring for and management of potential AMD waste rock seepage

• provisions to notify and respond to environmental and human health risks associated with water quality

• contingency plans to be implemented should monitoring identify an unacceptable impact.

The draft WMP should be closely related to but separate from a draft ESCP for the Project.

WRM (2018b)

The EIS should include how potential impacts and risks to downstream water quality will be managed post-mining, including post-mining monitoring and reporting to be used to evaluate rehabilitation success and progress toward achieving closure objectives and contingency measures to be implemented in the event that monitoring demonstrates that rehabilitation closure objectives are not being met.

Section 10



3 Existing environment

3.1 REGIONAL DRAINAGE CHARACTERISTICS The Project is located in the upper catchment of the Hay River basin. The Hay River originates in the Dulcie Ranges and flows in a southeasterly direction towards the Simpson Desert. The Plenty River drains roughly parallel to the Hay River. Flows from the Hay and Plenty rivers would appear to converge at the southern edge of the Simpson Desert before eventually feeding into Lake Eyre. The total catchment area of the Hay River basin upstream of Lake Eyre (including the Plenty River catchment) is approximately 100,000 km2.

Figure 3.1 shows the drainage network of the Hay River catchment and its major tributaries, including the Plenty River, the Marshall River and Arthur Creek. The Hay River catchment is bounded by the Georgina River catchment to the north and northeast, and by the Todd and Finke rivers catchments to the west.

The catchment is sparsely populated with isolated communities. Land use is typically rural throughout the catchment, with some evidence of historical mining activities in small areas, particularly within the Project area.

The Project is located adjacent to Unca Creek, a tributary of Arthur Creek in the upper headwaters of the Hay River catchment. Arthur Creek and the Marshall River converge into the Hay River approximately 60 km southeast of the Project.



Figure 3.1 – Hay River basin drainage network



3.2 LOCAL DRAINAGE CHARACTERISTICS

3.2.1 General

Figure 3.2 shows the local drainage network in the vicinity of the Project. The Project area is incised by a number of ephemeral drainage features that generally flow only during runoff-producing rainfall events.

The only watercourse of note in the vicinity of Jervois project is Unca Creek. Unca Creek originates about nine kilometres upstream of the Project and joins Arthur Creek approximately 45 km southeast of the Project. Unca Creek has a catchment area of 21.8 km2 upstream of upstream of the Project area, with 17.1 km2 (78%) of this catchment being captured in Jervois Dam within the Project area. Downstream of Jervois Dam, the Unca Creek channel runs in an easterly direction through the northern portion of the Project area before turning southeast and crossing Lucy Creek Access Road.

A tributary of Unca Creek runs east through the southern portion of the Project area before joining the main creek channel approximately 1.5 km east of Lucy Creek Access Road. The southern Unca Creek tributary has a catchment area of 21.9 km2 upstream of the Unca Creek confluence.

The Unca Creek catchment upstream of Jervois Dam is steep and rocky, with poorly defined, sandy drainage features located along valley floors. Downstream of Jervois Dam, the catchment becomes flat and open, with wide expanses of sandy flats and spinifex grass, with scattered vegetation along the creek and drainage feature channels. It is likely that the

The Unca Creek channel downstream of Jervois Dam is generally about 10 m wide and less than 1m deep, with a sandy bed that would become mobile during flood events. Loose rock is evident in the bed of the Unca Creek channel at locations where depths and flow velocities increase (i.e. at constrictions or bends in the channel).

Figure 3.5 to Figure 3.7 show photos of the Unca Creek channel. Figure 3.8 to Figure 3.10 show photos of the Unca Creek tributary channel. The locations of these photos are shown in Figure 3.2.

3.2.2 Jervois Dam

Jervois Dam, located on Unca Creek near the western boundary of the Project, was constructed for previous mining operations and is the largest and most permanent surface water body in the Jervois Region (MBS, 2013). Jervois Dam currently has a storage capacity of 279 ML below the existing spillway level (367.38 mAHD), and a catchment area of approximately 17.1km2. The dam spillway is a narrow (less than 3m wide) rock chute that has been cut through the ridge at the northern end of the dam wall. A stage-storage relationship was developed for Jervois Dam and is shown in Figure 3.16.

Figure 3.3 shows a photo of the lake upstream of Jervois Dam. Figure 3.4 shows a photo of the bottom of the Jervois Dam spillway. The locations of these photos are shown in Figure 3.2. The Northern Territory Government operated a water level gauge in Jervois Dam between 1972 and 2010.

The structural stability of the existing dam wall is unknown. It appears that there is significant leakage through the dam wall, as there is strong vegetation growth and signs of sodden ground along the southern side of the valley downstream of the dam wall. The existing spillway chute is about 4 m below the crest of the existing dam wall.

3.2.3 Historical mining activities

The Jervois Project tenements have been subject to historic mining and exploration activities by various companies since 1929. A copper mine operated in the area from 1963 to 1977 and historic mining disturbance exists including tailings storage dams, a waste rock dump, processing plant equipment, an open cut mining pit, numerous prospecting trenches, a ROM pad area and some ore stockpiles.



There is currently an operational exploration camp at the Project area.

Figure 3.11 shows a photo of the existing Marshall Reward open cut pit. Figure 3.12 shows a photo of the existing process plant equipment, taken from the existing ROM pad. Figure 3.13 and Figure 3.14 shows photos of the old tailings storage dams. The locations of these photos are shown in Figure 3.2.

The following key points are of note with regards to runoff from the existing mining disturbance areas:

• Runoff from the existing process plant area and ROM pad (including any remaining ore stockpiles) would drain north into Unca Creek;

• Runoff from the existing tailings dams would collect in the base of the dams and evaporate or seep from the base of the dams potentially to Unca Creek;

• Runoff from the existing waste rock dump drains south into the Tributary of Unca Creek;

• Runoff from the existing Green Parrot Pit would collect in the base of the pit and evaporate or seep into the underlying rock. The existing pit is about 9m deep at its deepest point.

• The prospecting trenches are generally located within the rocky outcrops in the southern portion of the Project area and would collect small amounts of runoff that would evaporate or seep into the underlying rock.



Figure 3.2 – Local drainage network in the vicinity of the Project



Figure 3.3 – Photo A – Jervois Dam water surface, looking west

Figure 3.4 – Photo B – downstream of Jervois Dam spillway



Figure 3.5 – Photo C – Unca Creek channel at the proposed Reward Pit location

Figure 3.6 – Photo D – Unca Creek channel at the proposed Reward Pit location



Figure 3.7 – Photo E – Unca Creek channel, with monitoring site JSW10

Figure 3.8 – Photo F – Unca Creek tributary channel, with monitoring site JSW07



Figure 3.9 – Photo G – Unca Creek tributary channel, with monitoring site JSW05

Figure 3.10 – Photo H – Unca Creek tributary channel



Figure 3.11 – Photo I – existing Green Parrot open cut pit

Figure 3.12 – Photo J – existing processing plant taken from ROM pad



Figure 3.13 – Photo K – old tailings storage dam

Figure 3.14 – Photo L – old tailings storage dam



3.3 CLIMATIC DATA

3.3.1 Overview

The climate of the Jervois area is arid, with rainfalls predominantly occurring in summer between October and March. Summers are hot with average maxima in the high thirties reducing to low twenties at night, and winters are mild with daily maxima in the mid-twenties and cooling to around 5°C at night. Temperatures of over 45°C in December and January and as low as -5°C in July have been recorded at the Bureau of Meteorology’s (BoM’s) Jervois Station (Station No. 15602) (MBS, 2013).

3.3.2 Rainfall

Figure 3.1 shows the locations of two rainfall stations located in the vicinity of the Project. The Jervois Station (Station No. 15602) is located about 35 km southwest of the Jervois Project area adjacent to the Marshall River. The Jervois Dam gauge (Gauge No. R0070009) is at Jervois Dam within the Project area.

Long term daily rainfall data recorded at the Jervois Station (Station No. 15602) was obtained from the Queensland Government DSITIA Patch Point data service. The Patch Point data provides a continuous daily data set between January 1889 and December 2017 (129 years). The Patch Point data contains recorded climate data at the Jervois Station for when data is available, with missing values derived by interpolation of recorded climate data between regional stations.

Recorded daily rainfall data at the Jervois Dam gauge (Gauge No. R0070009) were obtained from the Northern Territory (NT) Government water portal for the period between October 1977 and December 2010 (33 full years between 1978 to 2017). This gauge is closest to the Project area, however, the data includes some periods (up to several months) where data is not available.

Table 3.1 compares long-term monthly rainfall averages for the Patch Point and Jervois Dam data for the common period (1978 to 2017) and for the entire 129-year patch point period. Figure 3.15 compares the annual distribution of average monthly rainfall for the Patch Point and Jervois Dam data.

Table 3.1 and Figure 3.15 show that the differences in average monthly rainfalls between the long-term (129-year) Patch Point data and the Jervois Dam (34-year) data are between 5% and 22% for the wetter months (November to April), and between 13% and 68% for the drier months (May to October). However, the Patch Point data correlates well with the Jervois Dam data during the period of available data at Jervois Dam (1977 to 2010). For the purpose of this assessment, the long-term (129-year) Patch Point data was adopted for characterising existing climatic conditions.

The average monthly rainfalls at the Project area exhibit distinct wet (October and March) and dry (April to September) seasons during the year, with a dry season low of 5.2 mm in August to a wet season high of 44.3 mm in February. The west season average monthly rainfalls (13.2 mm to 44 mm) are up to eight times higher than the equivalent dry season monthly rainfalls (5.2 mm to 13.3 mm). The Patch Point average annual rainfall over the period from 1889 to 2017 is approximately 227 mm.

3.3.3 Evaporation

Long term daily Morton’s Lake evaporation data was also obtained from DSITIA’s Patch Point data service for the period between 1889 and 2017 (at the Jervois Station). Table 3.1 shows the long-term monthly averages of Morton’s lake evaporation for the Patch Point data. Figure 3.15 compares the annual distribution of average monthly Morton’s lake evaporation for the available rainfall data.

The Patch Point average annual Morton’s lake evaporation at the Jervois Station is estimated to be approximately 1,900 mm, which is approximately 8.4 times the average annual rainfall. The evaporation rate is high throughout the year, with the highest



evaporation rates occurring in the months between October and March. Evaporation is generally much higher than rainfall in all months of the year.

Table 3.1 – Long-term Patch Point average monthly rainfall and evaporation

Month

Patch Point average monthly

Mlake evaporation (mm) (1889 - 2017)

Average monthly rainfall (mm)

Patch Point rainfall

(1889 - 2017)


(1978 - 2010)

Jervois Dam rainfall

(1978 - 2010)

Jan 225.7 37.0 48.5 47.0

Feb 191.6 44.3 55.3 47.2

Mar 182.2 25.7 27.8 27.1

Apr 136.9 12.8 18.7 15.6

May 101.1 13.3 18.9 17.0

Jun 80.7 9.4 11.3 6.5

Jul 90.7 9.7 15.9 16.6

Aug 119.6 5.2 4.7 3.1

Sep 151.9 6.5 9.6 9.6

Oct 189.8 13.2 17.1 15.1

Nov 205.2 18.1 22.8 23.1

Dec 224.2 31.9 37.5 36.5

Average annual 1899.7 227.2 288.2 264.5

Figure 3.15 – Distribution of Patch Point average monthly rainfall and evaporation

0

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age

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Patch Point rainfall (1889 - 2017)

Patch Point rainfall (1977 - 2010)

Jervois Dam rainfall (1977 - 2010)

Patch Point average monthly Mlakeevaporation (mm) (1889 - 2017)



3.4 STREAMFLOW

3.4.1 Overview

Recorded sub-daily water level data at the Jervois Dam gauge (Gauge No. R0070009) were obtained from the Northern Territory (NT) Government water portal for the period between 1972 and 2010 (the period of record). The recorded water level data was converted to stored volumes using a stage-storage relationship derived from LiDAR data (described in Section 3.4.2).

3.4.2 Jervois Dam stage-storage relationship

Figure 3.16 shows the adopted stage-storage relationship for Jervois Dam, which was derived based on the supplied LiDAR survey data. The LiDAR data indicated a standing water level of approximately 364.2 mAHD at the time of survey. The dam crest level is approximately 371.5 mAHD. The storage volume below 364.2mAHD was extrapolated based on the ground slopes around the edge of the standing water surface. Using this assumption, the floor of the dam is estimated to be about 363.0 mAHD.

Figure 3.16 – Adopted Jervois Dam stage-storage relationship

3.4.3 Existing streamflow characteristics

Figure 3.17 shows the recorded dam water level during the period of record. Figure 3.18 shows the recorded stored volumes during the period of record derived using the stage-storage relationship shown in Figure 3.16. Table 3.2 shows a statistical summary of daily maximum stored volumes in during the period of record. The data indicates that:

• Jervois Dam generally fills up rapidly during the wet season (between December and February) and then gradually decreases in volume during the remainder of the year via evaporation and/or seepage, but rarely empties completely.

• During the period of record, the dam is at least 3.5% full on 90% of all days, at least 21.5% full in 50% of all days and at least 76.4% full in 10% of all days.

• The dam’s storage capacity to the spillway (274.8 ML) is exceeded on 3% of all days in the period of record.

0 20 40 60 80 100 120 140

362

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364

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375

0 500 1,000 1,500 2,000 2,500 3,000 3,500

Surface area (ha)

Dam

sta

ge (

mAH

D)

Volume (ML)

Volume (ML) Surface area (ha) Dam floor (approximate) Dam spillway Dam crest



Figure 3.17 – Recorded water levels in Jervois Dam (1972 to 2010)

Figure 3.18 – Recorded volumes in Jervois Dam (1972 to 2010)

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Recorded water level (mAHD) Dam spillway Dam crest

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(ML)

Stored volume (ML) Dam spillway Dam crest



Table 3.2 – Statistical summary of daily maximum recorded volumes in Jervois Dam

Percent of days

Volume exceeded (ML) Note

99% 3.7 1.4% full

90% 9.6 3.5% full

50% 59.0 21.5% full

10% 210.0 76.4% full

3% 274.8 Full storage level (FSL)

1% 315.3 Dam spilling

3.5 AQUATIC ECOSYSTEMS The Landscape, Flora and Fauna Report (Low Ecological, 2018) for the Project states the following points with regards to aquatic ecosystems at the Project site:

• There are no records of aquatic fauna, such as fish or freshwater invertebrates, in the NT Fauna Atlas within a 20 km buffer of the Project area.

• However, it is highly likely that fish and aquatic invertebrates will occur in the watercourses within or surrounding the Project area following good rainfall. Burrows of fresh water land crabs, likely Holothuisiana transversa, were found in nearby Arthur Creek by Low and Strong (1985).

No aquatic fauna was detected at the Project site during any of the Low Ecological field surveys conducted between 2012 and 2018.

3.6 GEOLOGY Based on information provided in the NOI for the Project (MBS Environmental, 2013), the soils in the Jervois Project area generally consist of shallow sands and loams. Soils within the Project area may be further described as shallow and stony in the ranges, with alluvial loams at the base of the hills and sandy or clayey loams in the extensive undulating plains (MBS Environmental, 2013).

3.7 GROUNDWATER This section provides an overview of previous studies undertaken to characterise the hydrogeology of the Project area. Details of the existing groundwater environment are provided in the groundwater assessment report (CloudGMS, 2018).

Knight Piésold Pty Ltd previously conducted a preliminary hydrogeological assessment of the Jervois Project area (Knight Piésold, 2012). The main purpose of this assessment was to determine the potential for a borefield capable of extracting the projected process water shortfall (predicted to be around 25 to 40 L/s) in the vicinity of the project. This study concluded that the likelihood of a 25 L/s second sustained extraction is considered reasonable, but not proven in the Georgina Basin Sequence, and low to very low out of the Arunta Orogenic Domain (Knight Piésold 2012).

3.8 GROUNDWATER EXTRACTION LICENCES There are no current groundwater extraction licences associated with the Project area. Groundwater licencing is discussed in detail in the groundwater assessment report (CloudGMS, 2018).



3.9 SURFACE WATER QUALITY

3.9.1 Water quality data

Figure 3.19 shows the locations of 11 surface water quality monitoring sites across the Project area, including one monitoring site in Jervois Dam and 10 monitoring sites in the catchment of Unca Creek and its tributary downstream of Jervois Dam (JSW001 to JSW010). Few samples are available for each monitoring site (generally between one and four), while no data is available for the JSW03 monitoring site. The available samples were obtained following a total of four rainfall events which occurred between 2015 and 2018, except for one sample for Jervois dam which was obtained in January 1991.

Table 3.3 provides a summary of water quality data obtained from these 11 monitoring sites. The data shows that:

• Water sampled in Jervois Dam is slightly acidic but close to neutral (pH of 6.7 to 6.9), with low EC, TSS and turbidity. Metal concentrations (total) are also below the detection limit for most metals. Contaminant concentrations in Jervois Dam are generally similar between the two samples taken in 1991 and 2018 respectively.

• Immediately downstream of Jervois Dam (site JSW06 and JSW02), water quality is similar to that observed in Jervois Dam, with pH close to neutral, low EC, TSS and turbidity as well as low concentrations of metals. However, the maximum sulphate concentration at JSW06 (17.3 mg/L) is significantly higher than those observed at all other sites (which range from 0.2 mg/L to 5.4 mg/L). The reason for this spike in sulphate concentrations is unknown.

• In Unca Creek at the eastern boundary of the Project area (at Lucy Creek Road) (site JSW10), pH (6.8) is slightly acidic but close to neutral. However, there is a noticeable increase in TSS and turbidity compared to samples taken from upstream sites. Metal concentrations are also significantly higher (compared to samples taken upstream) for all metal indicators except for aluminium and magnesium. Runoff from the old processing plant area and ROM pad reports to Unca Creek upstream of the JW10 monitoring site.

• At sites JSW04 and JSW05, located in the northern half of the catchment of the Unca Creek tributary, pH is slightly acidic (ranging from 6.2 to 6.8). EC is low, but TSS is relatively high, particularly in JSW04 (ranging from 1,540 mg/L to 3,180 mg/L). Metal concentrations at these sites are detectable, but are lower than metal concentrations observed in Unca Creek (sites JSW09 and JSW10). The catchments draining to JSW04 and JSW05 are undisturbed.

• At sites JSW08 and JSW07, located in the southern half of the catchment of the Unca Creek tributary, pH is neutral to slightly acidic (ranging from 6.5 to 7.1), while EC is low (ranging from 10 μS/cm and 35 μS/cm). TSS, turbidity and metal concentrations high considering the undisturbed nature of the catchments.

• In the Unca Creek tributary at the eastern boundary of the Project area (at Lucy Creek Road) (JSW01) pH ranges from 6.5 to 7.4, while EC is low. TSS and turbidity are higher compared to all other sites except for JSW09. Metal concentrations observed here are generally higher compared to all other sites except for JSW09. It is possible that runoff from the existing waste rock dump reports to the JSW01 monitoring site.

• East of the Project area and downstream of the confluence of Unca Creek and is tributary (site JSW09), pH is neutral to slightly acidic (ranging from 6.4 to 7.0), while EC is low. TSS and turbidity are higher compared to all other sites. Metal concentrations are also generally higher compared to all other sites.

3.9.2 Grouped water quality data

Table 3.4 shows a summary of water quality data for the following two groups of samples:



• Group A – This group consists of 8 samples obtained from monitoring sites located in the undisturbed areas within the Unca Creek Tributary catchment (sites JSW04, JSW05, JSW07 and JSW08).

• Group B – This group consists of 3 samples obtained from monitoring sites located in the undisturbed areas in Unca Creek immediately downstream of Jervois Dam (sites JSW02 and JSW06).

The data shows that water quality of Group B is similar to that observed in Jervois Dam, with pH close to neutral, low EC, TSS and turbidity as well as low concentrations of metals. Contaminant concentrations in Group A are significantly higher than Group B, particularly TSS and metals. The Group A monitoring sites are located in the mineralised zone within the Project area, which likely contributes to the high concentrations of metals at these monitoring sites. The increased turbidity and TSS at the Group B locations is due to the flat, sandy nature of the channel and floodplain at those sites, compared to the rock catchment prevalent around the Group A sites.

3.9.3 Summary of water quality characteristics

In summary, water quality at the Project area is characterised as follows:

• Across the Project area, pH is slightly acidic, while salinities (ECs) are low.

• Water stored in Jervois Dam has low turbidity as well as low concentrations of TSS, TDS and metals. This was expected as the catchment upstream of the dam is located outside of the mineralised region of the Project area. Water quality immediately downstream of Jervois Dam (monitoring sites JSW02 and JSW06) is consistent with the observed water quality in the dam.

• In the undisturbed areas along the Unca Creek Tributary (monitoring sites JSW04, JSW05, JSW07 and JSW08), turbidity is relatively high, while concentrations of TSS and metals are also relatively high. The catchment upstream of these monitoring sites is located within in the mineralised region of the Project area. This likely resulted in the elevated metal concentrations observed here despite the absence of mining disturbance in the contributing catchment.

• Downstream of the Project area (monitoring sites JSW01, JSW09 and JSW10), contaminant concentrations are consistent with those observed in the undisturbed areas along the Unca Creek Tributary. Runoff from the mineralised zone within the Project area reports to these monitoring sites. It is possible that runoff from existing mining disturbance in the catchment of Unca Creek and its tributary may have also contributed to the elevated contaminant concentrations observed here.



Figure 3.19 – Locations of baseline surface water quality monitoring sites



Table 3.3 – Water quality data for the watercourses across the Project area

Monitoring Site No. Statistic

Non-metallic indicators Metals and metalloids (total, except Mg)

pH

EC (

μS/c

m)

Tota

l sus

pend

ed

solid

s (m

g/L)

Tota

l dis

solv

ed

solid

s (m

g/L)

Turb

idit

y (N

TU)

Dis

solv

ed o

xyge

n (%

sat

urat

ion)

Sulp

hate

(m

g/L)

Nit

rate

(m

g/L)

Alu

min

ium

(μg

/L)

Ars

enic

(μg

/L)

Cadm

ium

(μg

/L)

Copp

er (

μg/L

)

Iron

(μg

/L)

Lead

(μg

/L)

Mag

nesi

um

(filt

ered

) (m

g/L)

Man

gane

se (

μg/L

)

Mer

cury

(μg

/L)

Nic

kel (

μg/L

)

Zinc

(μg

/L)

JSW01

N 3 3 3 3 3 n/a 3 3 2 3 3 3 2 3 3 3 3 3 3

Min. 6.5 26 2,520 20 530 n/a 0.4 0.010 <10 2.0 0 75 160 32 0.7 50 <0.1 32 130

Max. 7.4 67 6,980 50 1390 n/a 1.3 0.085 <10 73.4 58 120 250 71 1.8 680 88.1 72 340

Mean 6.8 47 4,147 37 1097 n/a 0.9 0.037 <10 47.9 35 93 205 52 1.2 260 53.1 53 237

JSW02

N 2 2 2 2 2 n/a 2 2 2 1 2 2 1 2 2 2 1 2 2

Min. 6.4 39 100 20 100 n/a 1.5 0.005 <10 13.0 36 5 10 3 0.6 <50 12.3 4 10

Max. 6.6 39 380 30 250 n/a 2.5 0.010 <10 13.0 54 15 10 17 1.1 <50 12.3 8 50

Mean 6.5 39 240 25 175 n/a 2.0 0.008 <10 13.0 45 10 10 10 0.9 <50 12.3 6 30

JSW03

N n/a

Min. n/a

Max. n/a

Mean n/a

JSW04

N 2 2 2 2 2 n/a 2 2 2 2 2 2 2 2 2 2 2 2 2

Min. 6.2 29 1,540 10 730 n/a 0.7 0.005 <10 40.2 42 45 40 25 0.6 <50 40.7 28 110

Max. 6.5 52 4,820 30 760 n/a 0.7 0.030 <10 48.1 46 50 40 28 0.9 <50 46.9 36 140

Mean 6.4 41 3,180 20 745 n/a 0.7 0.018 <10 44.2 44 48 40 27 0.8 <50 43.8 32 125

JSW05

N 2.0 2 2 2 2 n/a 2.0 2.000 2 1.0 2 2 1 2 2.0 2 1.0 2 2

Min. 6.4 30 20 20 61 n/a 1.6 0.005 <10 50.3 40 5 40 2 0.6 <50 46.8 <2 <10

Max. 6.8 47 1,880 30 1160 n/a 2.0 0.285 <10 50.3 52 50 40 44 0.7 <50 46.8 32 180

Mean 6.6 39 950 25 611 n/a 1.8 0.145 <10 50.3 46 28 40 23 0.7 <50 46.8 17 95



Table 3.3 - Water quality data for the watercourses across the Project area (continued)



pH

EC (

μS/c

m)

Tota

l sus

pend

ed

solid

s (m

g/L)

Tota

l dis

solv

ed

solid

s (m

g/L)

Turb

idit

y (N

TU)

Dis

solv

ed o

xyge

n (%

sat

urat

ion)

Sulp

hate

(m

g/L)

Nit

rate

(m

g/L)

Alu

min

ium

(μg

/L)

Ars

enic

(μg

/L)

Cadm

ium

(μg

/L)

Copp

er (

μg/L

)

Iron

(μg

/L)

Lead

(μg

/L)

Mag

nesi

um (

mg/

L)

Man

gane

se (

μg/L

)

Mer

cury

(μg

/L)

Nic

kel (

μg/L

)

Zinc

(μg

/L)

JSW06

N 1 1 1 1 1 n/a 1 1 1 n/a 1 1 1 1 1 1 n/a 1 1

Min. 7.1 137 110 110 8 n/a 17.3 <0.02 <10 n/a 38 <5 <10 <1 4.2 <50 n/a 2 <10

Max. 7.1 137 110 110 8 n/a 17.3 <0.02 <10 n/a 38 <5 <10 <1 4.2 <50 n/a 2 <10

Mean 7.1 137 110 110 8 n/a 17.3 <0.02 <10 n/a 38 <5 <10 <1 4.2 <50 n/a 2 <10

JSW07

N 2 2 2 2 2 n/a 2 2 1 2 2 2 1 2 2 1 2 2 2

Min. 6.2 25 2,790 30 800 n/a 0.7 0.175 <10 2.5 0 60 460 44 0.7 <50 0.1 46 200

Max. 7.1 35 3,490 30 860 n/a 0.8 0.485 <10 56.9 56 140 460 44 0.9 <50 60.7 48 260

Mean 6.7 30 3,140 30 830 n/a 0.8 0.330 <10 29.7 28 100 460 44 0.8 <50 30.4 47 230

JSW08

N 2 2 2 2 2 n/a 2 2 1 2 2 2 1 2 2 2 2 2 2

Min. 6.5 10 1,400 10 350 n/a 0.2 0.005 <10 1.5 0 45 80 16 0.2 <50 <0.1 16 60

Max. 7.1 26 4,090 10 670 n/a 0.9 0.210 <10 35.0 44 60 80 24 0.4 585 40.3 26 120

Mean 6.8 18 2,745 10 510 n/a 0.6 0.108 <10 18.3 22 53 80 20 0.3 318 20.2 21 90

JSW09

N 4 4 4 4 4 n/a 4 4 4 4 4 4 2 4 4 3 4 4 4

Min. 6.4 18 410 10 420 n/a 0.3 0.010 <10 1.5 0 50 170 17 0.5 <50 <0.1 22 100

Max. 7.0 75 9,090 60 1730 n/a 1.3 0.215 10 104.0 58 470 280 106 1.8 815 114.0 98 360

Mean 6.8 40 3,788 33 1113 n/a 0.8 0.070 10 41.7 27 178 225 60 1.0 305 44.1 54 225

JSW010

N 1 1 1 1 1 n/a 1 1 1 1 1 1 1 1 1 1 1 1 1

Min. 6.8 62 2,120 40 1420 n/a 1.7 0.015 <10 46.8 40 55 930 370 1.4 <50 54.5 44 320

Max. 6.8 62 2,120 40 1420 n/a 1.7 0.015 <10 46.8 40 55 930 370 1.4 <50 54.5 44 320

Mean 6.8 62 2,120 40 1420 n/a 1.7 0.015 <10 46.8 40 55 930 370 1.4 <50 54.5 44 320



Table 3.3 - Water quality data for the watercourses across the Project area (continued)



pH

EC (

μS/c

m)

Tota

l sus

pend

ed

solid

s (m

g/L)

Tota

l dis

solv

ed

solid

s (m

g/L)

Turb

idit

y (N

TU)

Dis

solv

ed o

xyge

n (%

sat

urat

ion)

Sulp

hate

(m

g/L)

Nit

rate

(m

g/L)

Alu

min

ium

(μg

/L)

Ars

enic

(μg

/L)

Cadm

ium

(μg

/L)

Copp

er (

μg/L

)

Iron

(μg

/L)

Lead

(μg

/L)

Mag

nesi

um (

mg/

L)

Man

gane

se (

μg/L

)

Mer

cury

(μg

/L)

Nic

kel (

μg/L

)

Zinc

(μg

/L)

Jervois Dam (03/03/2018) (see note a)

N 1 1 1 1 1 n/a 1 1 1 1 n/a 1 1 1 1 n/a n/a 1 1

Min. 6.7 106 80 80 7 n/a 5.4 0.260 <10 1.0 n/a <5 <10 <1 2.8 n/a n/a 2 <10

Max. 6.7 106 80 80 7 n/a 5.4 0.260 <10 1.0 n/a <5 <10 <1 2.8 n/a n/a 2 <10

Mean 6.7 106 80 80 7 n/a 5.4 0.260 <10 1.0 n/a <5 <10 <1 2.8 n/a n/a 2 <10

Jervois Dam (10/01/1991) (see note b)

N 1 1 1 1 1 n/a 1 1 n/a n/a n/a n/a 1 n/a 1 n/a n/a n/a n/a

Min. 6.9 170 72 125 26 n/a 7 8 c n/a n/a n/a n/a 4.1 n/a 4.0 n/a n/a n/a n/a

Max. 6.9 170 72 125 26 n/a 7 8 c n/a n/a n/a n/a 4.1 n/a 4.0 n/a n/a n/a n/a

Mean 6.9 170 72 125 26 n/a 7 8 c n/a n/a n/a n/a 4.1 n/a 4.0 n/a n/a n/a n/a a – Data obtained from surface water sampling undertaken by KGL in March 2018. b – Data obtained from the NT government water portal for the Jervois Dam gauge. c – Nitrate concentration appears inconsistent compared to data from other monitoring sites.

n/a – No available data



Table 3.4 – Grouped water quality data for undisturbed areas in Unca Creek and the Unca Creek Tributary

Monitoring Site Group

(Site #) Statistic

Non-metallic indicators Metals and metalloids (total)

pH

EC (

μS/c

m)

Tota

l sus

pend

ed

solid

s (m

g/L)

Tota

l dis

solv

ed

solid

s (m

g/L)

Turb

idit

y (N

TU)

Dis

solv

ed o

xyge

n (%

sat

urat

ion)

Sulp

hate

(m

g/L)

Nit

rate

(m

g/L)

Alu

min

ium

(μg

/L)

Ars

enic

(μg

/L)

Cadm

ium

(μg

/L)

Copp

er (

μg/L

)

Iron

(μg

/L)

Lead

(μg

/L)

Mag

nesi

um

(filt

ered

) (m

g/L)

Man

gane

se (

μg/L

)

Mer

cury

(μg

/L)

Nic

kel (

μg/L

)

Zinc

(μg

/L)

Undisturbed areas in the Unca Creek Tributary

N 8 8 8 8 8 n/a 8 6 6 7 6 7 5 8 8 1 6 7 7

Group A 20%ile 6.3 25 1,456 10 35 n/a 0.7 0.030 <10 9.0 42 46 40 19 0.5 n/a 40.3 26 112 (JSW04, JSW05, Median 6.5 30 2,335 25 43 n/a 0.8 0.193 <10 40.2 45 50 40 27 0.7 n/a 43.8 32 140

JSW07, and JSW08) 80%ile 7.0 42 3,850 30 68 n/a 1.3 0.285 <10 49.9 52 60 156 44 0.8 n/a 46.9 44 196

Mean 6.6 32 2,504 21 50 n/a 1.0 0.198 <10 33.5 47 64 132 28 0.6 585 39.3 33 153

Undisturbed areas in Unca Creek N 3 3 3 3 3 n/a 3 1 3 1 3 1 1 3 3 3 1 3 2

Group B Min. 6.4 39 100 20 8 n/a 1.5 0.010 <10 13.0 36 15 10 2 0.6 <50 12 2 10 (JSW02 and

JSW06) Max. 7.1 137 380 110 250 n/a 17.3 0.010 <10 13.0 54 15 10 8 4.2 <50 12.3 8 50

Mean 6.7 72 197 53 119 n/a 7.1 0.010 <10 13.0 43 15 10 5 2.0 <50 12.3 5 30



4 Environmental values and water quality objectives

4.1 ENVIRONMENTAL VALUES Environmental values (EVs) are the qualities of waterways to be protected from activities in the catchment. Protecting environmental values aims to maintain healthy aquatic ecosystems and waterways that are safe and suitable for community use. Environmental values reflect the ecological, social and economic values and uses of the waterway (such as stock water, cultural uses, maintaining biodiversity, fishing and agriculture).

The processes to identify EVs and determine water quality objectives (WQOs) are based on the National Water Quality Management Strategy: Implementation Guidelines (NWQMS, 1998). They are further outlined in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC & ARMCANZ, 2000).

There are no currently prescribed EVs for the Project Area. Therefore, based on the NWQMS (1998) and ANZECC & ARMCANZ (2000) guidelines, the following EVs are proposed for the Project:

• aquatic ecosystems;

• primary industries including stock drinking water, irrigation and general water uses;

• recreation and aesthetics; and

• cultural and spiritual values.

4.2 WATER QUALITY OBJECTIVES

4.2.1 Adopted water quality objectives

Based on the ANZECC & ARMCANZ (2000) guideline, the condition of the watercourses in the vicinity of the Project is considered as Condition 2: slightly to moderately disturbed ecosystem. The adopted surface water quality indicators relevant to meeting the above EVs are sourced from the ANZECC & ARMCANZ (2000) guideline.

Table 4.1 shows the adopted water quality objectives (WQOs) for the receiving waters downstream of the Project. It is anticipated that these WQOs will be applied to any waste discharge licence issued for the Project site.

The ANZECC & ARMCANZ (2000) WQOs for aquatic ecosystems are considered to be the most conservative of the EVs listed above and have therefore been adopted as the surface water WQOs for most parameters. Where no aquatic ecosystem WQO value is available for a certain parameter, a WQO has been sourced from alternative EVs (as listed in Section 4.1). WQOs for pH, electrical conductivity (EC), turbidity, dissolved oxygen (DO), sulphate and iron were sourced from ANZECC & ARMCANZ (2000) guidelines for either livestock drinking water or recreation.

The following is of note with regards to the adopted WQOs:

• The WQOs in Table 4.1 were obtained from the ANZECC & ARMCANZ (2000) guideline for aquatic ecosystems based on 95% of species level of protection, except for pH, EC, turbidity, DO, sulphate, nitrate and iron.

• The ANZECC & ARMCANZ (2000) recommended pH level for general water uses is between 6 and 8.5 for groundwater and between 6 and 9 for surface water. The recommended pH limit of between 6 and 8.5 is adopted for the Project.



• The adopted WQO limits for EC and sulphate are based on the ANZECC & ARMCANZ (2000) guidelines for livestock drinking water.

• In absence of more site-specific guidelines, the adopted turbidity limit is based on the ANZECC & ARMCANZ (2000) guidelines for upland and lowland rivers in south central Australia: low rainfall area.

• In absence of more site-specific guidelines for arid regions, the adopted DO (%) limit is based on the ANZECC & ARMCANZ (2000) guidelines for freshwater lakes and reservoirs in south central Australia: low rainfall area. No data is available in the guideline for upland rivers, which would have been more representative of the Project area.

• The WQO limit for iron is based on the ANZECC & ARMCANZ (2000) guidelines for recreational purposes.

The adopted WQO limits will be revised once a suitable number of water quality samples are available from the background surface water monitoring stations at the Project (JSW04, JSW05, JSW02 and JDW06) to develop site specific WQOs. The current background water quality sampling data is not suitable for deriving site specific WQOs as no filtered metalloid concentrations have been measures (only total metal concentrations are available).

There are no WQOs available for total suspended solids (TSS). Background TSS concentrations are very high in both Unca Creek (Group B monitoring sites) and Unca Creek Tributary (Group A monitoring sites). The sampled TSS concentrations in Group A are significantly less than those for Group B, which reflects the differences in catchment type. The maximum sampled TSS concentration in Group A monitoring sites has been conservatively adopted as the WQO. It is likely that parameters other than TSS will determine releases of water at the Project.

4.2.2 Comparison of WQOs against observed water quality

Table 4.1 compares the adopted WQOs against the 80th percentile observed water quality for Group A monitoring sites, which consists of 11 samples obtained from undisturbed areas within the Project area. The data indicates that:

• Observed water quality parameters are within the WQO limits for pH, EC, TDS, sulphate, nitrate and magnesium. However, the observed turbidity is significantly higher than the WQO limit.

• Metal concentrations for all other metalloids (except magnesium) were not measured for filtered samples, therefore the observed metal concentrations (total metals) cannot be directly compared with the WQOs (filtered metals).



Table 4.1 – Adopted surface water quality objectives (WQOs) for the Project, and comparison with observed water quality data

Parameter Abbreviation Units Adopted WQO value a

Group A observed water quality (80%ile) (see Table 3.4) i

Non-metallic indicators

pH pH pH units 6.0 - 8.5 b 7.1

Electrical conductivity EC μS/cm 5,970 c 42

Total dissolved solids TDS mg/L 4,000 c 30

Total suspended solids TSS mg/L 380 k 3,850

Turbidity Turbidity NTU 50 d 1,160

Dissolved oxygen DO % saturation 90 e n/a

Sulphate SO4 mg/L 1,000 f 1.3

Nitrate NO3 mg/L 0.7 0.240

Metals and metalloids (filtered, unless otherwise stated)

Aluminium Al μg/L 55 <10 (total) j

Arsenic As μg/L 24 59.2 (total) j

Cadmium Cd μg/L 0.2 54 (total) j

Copper Cu μg/L 1.4 92 (total) j

Iron Fe μg/L 300 g 232 (total) j

Lead Pb μg/L 3.4 44 (total) j

Magnesium Mg mg/L 2,000 h 0.9

Manganese Mn μg/L 1,900 661 (total) j

Mercury Hg μg/L 0.6 66.9 (total) j

Nickel Ni μg/L 11 49 (total) j

Zinc Zn μg/L 8 244 (total) j a – Obtained from Table 3.4.1 in ANZECC & ARMCANZ (2000) based on 95% species level of protection, unless otherwise stated. b – Section 4.2.10.1 in ANZECC & ARMCANZ (2000) for general water uses. c – Table 4.3.1 in ANZECC & ARMCANZ (2000), adopted the lower limit for beef cattle and horses. d – Table 3.3.9 in ANZECC & ARMCANZ (2000) for upland & lowland rivers. e – Table 3.3.8 in ANZECC & ARMCANZ (2000) for lowland rivers and freshwater lakes and reservoirs. f – Section 4.3.3.4 in ANZECC & ARMCANZ (2000) for livestock drinking water. g – Table 5.2.3 in ANZECC & ARMCANZ (2000) for recreational purposes. h – Section 4.3.3.2 in ANZECC & ARMCANZ (2000) for livestock drinking water. i – Group A sites are representative of undisturbed areas within the mineralised zone of Project area. j – Testing on filtered samples was not undertaken. k – No WQO values for TSS available, maximum sample TSS concentration from Sample group B nominated



5 Project description

5.1 MINING AREAS AND OPERATIONS Mining operations at the Project area will be split between three operational areas (refer Figure 5.1):

• Reward;

• Bellbird; and

• Rockface.

Mining at Reward and Bellbird is both open cut and underground, whilst Rockface is underground only. Ore from all three mining areas will be trucked to the ROM stockpile for processing at the plant.

The Marshall Reward mining area is located in the catchment of Unca Creek, whilst the Bellbird and Rockface mining areas are located in the upper catchment of the Unca Creek tributary.

5.2 PROPOSED INFRASTRUCTURE Figure 5.1 shows the proposed infrastructure for the Project area, which is described below.

5.2.1 Reward infrastructure

Major infrastructure at the Reward operational area consists of:

• A main open cut pit located across the main channel and floodplain of Unca Creek;

• A permanent diversion channel for Unca Creek;

• Three minor satellite pits located north of the main open cut pit;

• An underground mining operation with the portal located towards the base of the main open cut pit;

• A waste rock dump; and

• Sediment dams to capture runoff from the water rock dump.

5.2.2 Bellbird infrastructure

Major infrastructure at the Bellbird operational area consists of:

• Two main open cut pits referred to as Bellbird North Pit and Bellbird South Pit;

• Two minor satellite pits located close to the Bellbird South Pit;

• An underground mining operation with the portal located towards the base of the Bellbird South Pit;

• A waste rock dump; and

• Sediment dams to capture runoff from the water rock dump.

5.2.3 Rockface infrastructure

The only infrastructure of note located at the Rockface operation area will be the underground mine and associated portal and haul roads.



Figure 5.1 – Jervois project layout



5.2.4 Jervois Dam

The existing Jervois Dam will be repaired as part of the Project, to improve the structural stability of the wall, reduce leakage and increase storage capacity.

5.2.5 Process plant

A new process plant will be constructed at the site of the existing process plant south of Unca Creek. The process plant area will include ROM and product stockpile areas, process plant infrastructure, chemical storage and associated hardstand. A process water dam will be constructed adjacent to the Unca Creek diversion channel.

5.2.6 Tailings storage facility

A new tailing storage facility will be constructed at the site of the existing tailings dams to the west of the process plant.

5.2.7 Accommodation camp and administration

An accommodation camp and administration office will be constructed in the southeastern portion of the project area.

5.3 PROJECT STAGING Mine schedules for the Project have been provided for 10 representative Project years, indicating a mine life of 10 years. The provided mine schedules for key stages of the Project life are shown in Figure A.1 to Figure A.10 in Appendix A. Table 5.1 summarises the three key stages of the Project life.

The proposed mine sequence is summarised as follows:

• At the start of mining (EOY0):

o Open cut mining will commence at the Reward open cut pit; and

o Underground mining will commence at Rockface, and will continue until the end of year 7 (EOY7).

• At the end of year 4 (EOY4):

o underground mining will commence at the Reward Pit, while open cut mining will continue simultaneously until the end of year 5 (EOY5); and

o open cut mining will commence at the Bellbird North and South pits, and will continue until the end of year 8 (EOY8).

• At the end of year 5 (EOY5), open cut mining will cease at the Reward Pit, while underground mining will continue until the end of year 10 (EOY10).

• At the end of year 6 (EOY6), underground mining will commence at the Bellbird South Pit, while open cut mining will continue until the end of year 8 (EOY8).

• At the end of year 7 (EOY7), underground mining will cease at the Rockface Pit.

• At the end of year 8 (EOY7), open cut mining will cease at the Bellbird Pit, while underground mining will continue until the end of year 10 (EOY10).

• At the end of year 10 (EOY10), underground mining will cease at the Reward and Bellbird pits.



Table 5.1 – Adopted mine stages

Project year

Marshall / Reward operations

Bellbird operations

Rockface operations

EOY0 to EOY4 open cut only none underground only

EOY4 to EOY5 open cut + underground open cut only underground only

EOY5 to EOY6 underground only open cut only underground only

EOY6 to EOY7 underground only open cut + underground underground only

EOY7 to EOY8 underground only open cut + underground none

EOY8 to EOY10 underground only underground only none



6 Proposed water management strategy and infrastructure

6.1 OVERVIEW The key objectives of the Project’s water management system are:

• To protect environmental values of the receiving waters downstream of the Project during the operational period and post-closure; and

• To ensure that the Project has sufficient water available for operations during dry times.

The water management system proposed for the Project has been designed to achieve these objectives, as discussed in the following sub-sections.

6.2 SURFACE WATER TYPES For surface water management purposes, the surface water that is generated and/or managed at the Project is divided into five classes based on water quality:

• Undisturbed runoff: runoff from catchments unaffected by mining;

• Raw water (potable standard): raw water suitable for use in supplying the potable water treatment plant. Raw water (potable) standard will not have been in contact with any areas disturbed by mining, or any ore bodies. Raw water (potable standard) is typically sourced from Jervois Dam or the external borefield.

• Raw water (plant standard): water suitable for use in the raw water streams of the process plant. Raw water (plant standard) will have suitably low levels of TSS to prevent clogging of machinery nozzles but may have elevated levels of metalloids. Raw water (plant standard) is typically sourced from groundwater dewatered from the underground mining operations.

• Sediment laden water: sediment laden runoff from waste rock dumps. Sediment laden water is suitable for use as make-up process water in the plant, and for dust suppression. May be suitable for release to the environment dependant on long term water quality monitoring results.

• Mine affected water: runoff from areas where chemicals, contaminants or oxidised ore may be present. Includes runoff that collects from the process plant, ROM and product stockpiling areas, open cut mining pits and tailings storage facilities. Suitable for use as make up process water in the plant and for dust suppression. Unlikely to be suitable for release to the environment.

6.3 WATER MANAGEMENT PRINCIPLES The adopted principles for management of water on the site are summarised as follows:

• Existing surface water drainage patterns will be maintained where practical to do so;

• Water from different sources will be managed separately:

o Undisturbed runoff will be diverted around disturbed areas where practical;

o Mine affected water collected in-open cut pits, and in the process water dam will be managed using temporary in-pit sumps and re-used within the water management system;



o Sediment-laden runoff from the proposed waste rock dumps will be captured in dedicated sediment dams and re-used within the water management system;

o Raw water (plant standard) dewatered from the open cut pits and underground mines will be reused within the water management system.

• Water will be selected for use based on water quality considerations;

• Water collected on site as part of mining operations will be used preferentially in order to reduce demand on external water sources. Water for mine operating purposes (excluding supplying potable water) will be sourced preferentially as follows:

o Mine affected water;

o Sediment laden water;

o Raw water (plant standard), dewatered from the underground mines;

o Raw water (potable standard), sourced from Jervois Dam; and

o Raw water (plant standard) sourced from the external borefield.

6.4 CONTAMINANT SOURCE STUDY

6.4.1 Potential contaminant sources

Key potential sources of contaminants are listed in Table 6.1. The dams which capture runoff from these sources are also shown.

Table 6.1 – Contaminant sources and destinations of runoff

Contaminant source Contaminant type Destination water storage ROM and product stockpiles Sediment, metals Process water dam

Process plant industrial area Sediment, metals, chemicals, oil and

grease Process water dam

Open cut mining pits Sediment, metals Process water dam Waste rock dumps Sediment Sediment dams

6.4.2 Contaminant concentrations in site runoff

Water captured and stored in the site water management system would comprise a mixture of runoff water from various catchment land use types and groundwater from seepage into the underground mines. Full details of the water quality of water in the water management system will not be known until the project is operational.

The water quality characterisation described in the following sections has been used (in conjunction with the site water balance model) for the purposes of assessing the potential risks for the receiving waters.

Undisturbed Areas – surface runoff from undisturbed areas is likely to be of a similar quality to those samples monitoring stations JSW04, JSW05, JSW07 and JSW08. The data from these monitoring locations is detailed in Section 3.9 of this report. Runoff from undisturbed areas will be diverted around disturbance areas and released to the environment.

Water Storage Surfaces – direct rainfall onto water surfaces will have negligible dissolved salt/metal concentrations.

Runoff from ROM and product stockpiles (mine affected water) – runoff from the ROM and product stockpiles will likely have been in contact with exposed ore. It is likely this runoff would contain sediment and elevated levels of metals. It will not be suitable for release to the environment and will be collected and reused on site.



Runoff from process plant area (mine affected water) – runoff from the process plant area will likely have been in contact with ore, and may contain sediment, chemicals and oil and grease. It will not be suitable for release to the environment and will be collected and reused on site. Suitable at source controls will be implemented within the process plant area to contain oil and grease and chemicals:

• Appropriate bunding of all chemical stores; and

• Hydrocarbon capture and oil and grease separators.

Runoff from pit areas (mine affected water) – water collecting on the floor of the pits is likely to surface runoff that has been in contact with exposed ore. It is likely this runoff would contain sediment, elevated levels of metals and potentially oil and grease. It will not be suitable for release to the environment and will be collected and reused on site.

Groundwater seepage to underground mines (raw water plant standard)– Groundwater seepage into the underground mine will likely have been in contact with ore, and may contain elevated levels of metals. It will not be suitable for release to the environment and will be collected and reused on site.

Waste rock dumps (sediment laden water) – It is expected that runoff from the dumps will generally be of similar quality to background runoff from undisturbed catchments within the project site, and will not contain acid rock drainage or significantly elevated concentrations of metalloids (beyond background values). It is likely that the runoff from the waste rock dumps would be suitable for release to the environment. However, it is proposed to monitor runoff quality from the waste rock dumps for the first 4 years of Project life, and pump the contents of the sediment dams back to the mine water management system. If water quality monitoring indicates that runoff is of suitable quality, controlled releases of runoff to the environment (following runoff events) could be made from the sediment dams from year 5 of Project life.

6.5 WATER MANAGEMENT SYSTEM INFRASTRUCTURE A conceptual water management system (WMS) layout for the Project has been developed based on the water management principles described above, and is shown Figure 6.1 for the Reward operations and Figure 6.2 for the Bellbird operations. A schematised plan for the WMS configuration is shown in Figure 6.3.

Preliminary concept designs and locations have been developed for water management infrastructure, including clean and dirty water drains as well as proposed sediment dams. The key components of the proposed WMS are described below (refer to Figure 6.1 and Figure 6.2 for locations).

The proposed mine schedules show that the proposed Reward Pit and waste rock dump profiles will gradually change over the life of the mine, but the total footprint and catchments will remain the same. Similarly, the open cut pit and waste rock dumps footprint and catchments at the Bellbird operational area also appear to be unchanged from the start of mining at the end of year 4 (EOY4) to the end of the mine life. Therefore, the proposed WMS layout shown in Figure 6.1 (for the Reward operations) and Figure 6.2 (for the Bellbird operations) are considered representative for the entire life of the Jervois Project.

6.5.1 Unca Creek diversion

The Reward pit is located within the channel and floodplain of Unca Creek to north of the process plant. It is proposed to permanently divert Unca Creek north around the Reward pit.

The creek diversion will ensure that the Reward pit is protected from flows from the upstream catchment (including overflows from Jervois Dam) for events up to and including 0.1% AEP (1,000 years ARI). The final landform between the Reward pit and the creek diversion will ensure that the final void is protected from inundation for all flood events up to and including the Probable Maximum Flood (PMF) event.



Figure 6.1 – Proposed water management system (WMS) lay out for the Reward mining operations

Existing Green Parrot Pit



Figure 6.2 – Proposed water management system (WMS) layout for the Bellbird and Rockface mining operations



Figure 6.3 – Water management system schematic



Figure 6.1 shows that the proposed Satellite Pit 1 is located in the middle of the proposed creek diversion. Satellite Pit 1 will be mined first and then back-filled to allow the construction of the proposed creek diversion to service the later stages of mining.

6.5.2 Surface water storages

Table 6.2 lists the proposed surface water storages for the Project, including the catchment area draining to each storage, the proposed storage volume and the type of water held in each storage.

Table 6.2 – Surface water storages

Storage name Catchment area (ha)

Volume (ML) Water type

Underground dewatering dam NA 10.0 Raw water (plant standard) Process water dam 43.6 182.8 Mine affected water Sediment dam SD1 15.3 7.5 Sediment laden water Sediment dam SD2 27.5 13.5 Sediment laden water Sediment dam SD3 20.8 10.2 Sediment laden water Jervois dam 1,710 945.0 Raw water (potable standard)

6.5.2.1 Underground dewatering dam

An underground dewatering dam will be constructed adjacent to the process plant and process water dam. The underground dewatering dam will receive pumped dewatering flows from the underground mining operations at Reward, Bellbird and Rockface. This water is considered to be raw water (plant standard), and hence requires its own storage to ensure it does not mix with mine affected and sediment laden water that is stored in the process water dam.

The underground dewatering dam is a turkey nest storage (i.e. has no catchment except for the dam itself) and has a storage capacity of 10 ML. The underground dewatering dam overflows into the adjacent process water dam.

6.5.2.2 Process water dam

A process water dam will be constructed between the Unca Creek diversion channel, the Reward pit, and the process plant. The process water dam receives inflows from the following sources:

• Catchment runoff from a 43.6 ha mine affected water catchment that includes the process plant and ROM and product stockpiles, as well as the existing ROM pad and tailing storage dam;

• Pumped transfers of sediment laden water from the waste rock dump sediment dams;

• Pumped transfers of mine affected water from the open cut mining pits; and

• Overflows of raw water (plant standard) from the underground dewatering dam;

The process water dam will have a capacity of approximately 180 ML and will have emergency spillway to the adjacent Unca Creek diversion channel.

6.5.2.3 Waste rock dump sediment dams

Three sediment dams are proposed to capture runoff from waste rock dumps, including two sediment dams for the Reward waste rock dump (SD1 and SD2) and one sediment dam for the Bellbird waste rock dump (SD3). Sediment dams have been sized to capture all runoff from the waste rock dumps for a 10 % AEP 24-hour rainfall event.



Sediment laden runoff collected in the waste rock dump sediment dams will be pumped back to the process water dam or released to the environment if runoff is of suitable quality.

Sediment dams SD1 and SD2 both overflow into the Unca Creek diversion drain. Sediment Dam SD3 overflows into the upper reaches of the Unca Creek tributary.

6.5.2.4 Jervois Dam Repair

It is proposed to repair (and improve) Jervois Dam as part of the project. The repair will involve construction of an improved dam wall and spillway. The improved dam wall (373 mAHD) will limit leakage and improve dam safety during extreme events. The upgraded spillway will have capacity to pass the peak 0.1% (1 in 1,000) AEP discharge from the dam catchment without the wall becoming overtopped.

The spillway level will be raised to 370.0 mAHD to provide additional storage volume. The storage volume below the spillway will be increased to approximately 945 ML. The new spillway level will ensure that the sacred site located upstream of the dam will not be inundated by standing water. Figure 6.4 shows the stage-storage relationship for the repaired Jervois Dam.

The repaired Jervois Dam will be used as a source of raw water (potable standard) and will have a permanent pump and pipeline to the process plant and potable water treatment plant.

The timing of the repairs to the dam will be determined by a number of factors, including the need for additional raw water in the first 4 years of operations.

Figure 6.4 – Repaired Jervois Dam stage-storage relationship

6.5.3 Clean and dirty water diversion drains

Proposed clean water drains will be constructed to divert undisturbed runoff around disturbed areas. Key catchments to be diverted include undisturbed catchments upstream of and adjacent to the proposed Tailings Storage Facilities and upstream of the Reward and Bellbird waste rock dumps.

Proposed dirty water drains to capture and convey sediment laden runoff from waste rock dumps to the waste rock dump sediment dams.



Both clean and dirty water drains will be sized to convey all runoff from events up to and including 1 % AEP.

6.5.4 Tailings storage facility

The proposed tailings storage facility will be located at the site of the existing tailings dam to the west of the process plant and to the south of Unca Creek.

The design and operation of the tailings storage facility will be undertaken by others. The tailing storage facility will be designed to have sufficient storage capacity to contain all runoff from the tailings storage area.

The tailing storage facility will include a decant system to return water to the process plant.

6.5.5 External borefields

A borefield will be established external to the Project area to provide raw water (potable standard). CloudGMS (2018) proposes a borefield capable of producing up to 2,000 ML/year for 10 years. Bores will be completed into the Georgina Basin Carbonate Aquifer at a site 10km to the north of the mine site.

6.5.6 Haul and access road crossings

All haul and access road crossings of drainage features and waterways will be low level causeway crossings. No culverts are proposed for any crossings.

6.5.7 Potable water and wastewater treatment

A potable water treatment plant will be located at the Project to supply potable demands to the workforce. Wastewater from the accommodation camp and offices will be treated by a septic system, with disposal of treated effluent to ground in the vicinity of the camp.

6.6 GROUNDWATER INFLOWS

6.6.1 Open cut mining pit dewatering

Runoff and any groundwater seepage (mine affected water) collecting in the Reward and Bellbird open cut pits will be collected in sumps before being pumped out the process water dam.

CloudGMS (2018) provided estimates of the groundwater seepage rates for the Reward and Bellbird open cut pits. Evaporation from the pit surfaces will exceed the maximum predicted seepage rates to both pits, and hence net volume of groundwater that will need to be dewatered from the open cut pits is predicted to be zero.

6.6.2 Underground mine dewatering

Groundwater that seeps into the underground mining operations will be pumped to a collection sump at the portal of each mine before being pumped back to the underground dewatering dam. Groundwater that seeps into the underground mining operations is expected to be of good quality (suitable for use to supply raw water demands in the process plant (CloudGMS, 2018). Figure 6.5 shows the CloudGMS (2018) predicted groundwater inflow rates to each of the underground mines at the Project. The following is of note:

• Until the end of year 4, the only groundwater inflows are into the Rockface underground mine, which peaks at approximately 1,185 ML/year (3.2 ML/day) in year 4 of operations;

• Underground mining at Reward commences in year 5, and groundwater inflows to the Reward underground peak in year 7 at approximately 1,560 ML/year (4.4 ML/day);



• Underground mining commences at Bellbird in year 7, and groundwater inflows to the Bellbird underground peak in year 8 at approximately 585 ML/year (1.6 ML/day);

• The total groundwater inflow to the underground mines peaks in year 7 at 2,346 ML/year (6.4 ML/day); and

• Underground mining at Rockface is complete at EOY7, and it is not proposed to continue to dewater the Rockface underground mine beyond that point in time, however the Rockface underground will be used as a source of water as needed from EOY7 onwards.

Figure 6.5 – Predicted groundwater inflows to underground mines

6.6.3 Sensitivity of predicted groundwater inflows

CloudGMS (2018) indicates that the predicted groundwater inflows to the open cut pits and underground mines are particularly sensitive to the adopted hydraulic conductivity in the groundwater model.

CloudGMS (2018) states that groundwater inflows are forecast to decrease by a factor of about 40% due to a decrease in hydraulic conductivity, and conversely groundwater inflows are forecast to increase by a factor of about 40% due to an increase in hydraulic conductivity.

6.7 WASTE ROCK DUMP RUNOFF AND SEDIMENT DAMS The material placed in the waste rock dumps and the proposed dump construction methods will ensure that runoff from the dumps is generally of similar quality to background runoff from undisturbed catchments within the project site, and will not be contain acid rock drainage or significantly elevated concentrations of metalloids (beyond background values). Nevertheless, a cautionary approach has been adopted to the management of runoff from the waste rock dumps:

• During the first 4 years of project life, when groundwater inflows to the underground mine are low, runoff captured in the waste rock sediment dams will be pumped back to the process water dam;



• Surface runoff and seepage from waste rock dumps that collects in the sediment dams would be monitored for water quality parameters including, but not limited to pH, EC, major anions (sulfate, chloride and alkalinity), major cations (sodium, calcium, magnesium and potassium), TDS and a broad suite of soluble metals/metalloids;

• Uncontrolled releases (spills) from the waste rock sediment dams may still occur in the first four years of mining if the design criteria of the sediment dams is exceeded (i.e. a rainfall event greater than the 10% AEP 24-hour storm occurs whilst the waste rock dump catchments are saturated);

• The sediment dam monitoring would be used to validate the anticipated quality of water runoff reporting to sediment dams. Initially, the sediment dam monitoring would occur on an event basis to demonstrate the water quality of stored waters is consistent with the relevant operating parameters to allow releases from sediment dams to occur if required.

• Subject to demonstrating the water quality objectives can be met, the frequency of monitoring and suite of parameters for the sediment dam monitoring would be reviewed and updated accordingly (e.g. to occur only when releases occur); and

• It is anticipated that by EOY4 of mine life, sufficient water quality monitoring data would be available to determine if runoff and seepage from the waste rock dumps is suitable for release from the sediment dams following runoff events. If this is the case, then runoff captured in the waste rock sediment dams would no longer be pumped back to the process water dam and would be released to the receiving environment within 5 days of a runoff event occurring (as per best practice sediment dam operation).

• If water quality monitoring data indicates that waste rock dump runoff is not suitable for release, the sediment dams will continue to be pumped back to the process water dam beyond EOY4.

6.8 SITE WATER DEMANDS

6.8.1 Potable water demands

Based on the water mass balance process flow diagram for the Project (Sedgman, 2018) the predicted water demand rate to the Potable Water Treatment Plant is 3.8 T/h (0.1 ML/d or 36.5 ML/year). Based on a plant yield of 50%, 1.9 T/h (0.05 ML/d) of treated water from the Potable Water Treatment Plant will be used to supply potable water uses at the mine camp and the administration area. The remaining 1.9 T/h (0.05 ML/d) waste stream from the potable water treatment plant will be pumped to the process plant to supply non-potable uses.

6.8.2 Process plant demands

The Sedgman (2018) water mass balance shows the Process Plant is projected to require a constant water demand rate of 86.1 T/h (2.05 ML/d) over the life of the Project, which includes:

• 55 T/h (1.3 ML/d or 475 ML/year) of raw water (plant standard); and

• 31 T/h (0.75 ML/d or 274 ML/year) of process water (mine affected water or sediment laden water).

The above water demand rate has accounted for all internal recycling of processed water within the process plant and tailing storage facility. If insufficient mine affected or sediment laden water is available to supply the process water demand to the plant, raw water will be used to supply the plant demand.



6.8.3 Dust suppression

Dust suppression demand rates were calculated based on the predicted surface area (waste rock dump, open cut pits, haul roads and access roads) to be wetted, and the average daily evaporation rate for during dry days. The following methodology was adopted:

• For mining pit and waste rock dumps, dust suppression demand was calculated assuming that 50% of the total area require dust suppression. Dust suppression is not required when the open cut pit or waste rock dump is no longer in operation.

• For haul roads and access roads, dust suppression demand was calculated based on a total road length of 13.9 km and road width of 30 m as per the proposed haul road layout supplied by KGL. The total road surface area requiring dust suppression will remain the same over the life of the Project.

• Based on the 129-year Patch Point data, there is an average of 354 dry days per year, and an average daily evaporation rate of 5.6 mm during these dry days. The daily dust suppression rate for each mine stage was calculated by multiplying the average daily evaporation rate (5.6 mm) and the surface area requiring dust suppression.

Table 6.3 shows the adopted dust suppression demand rates over the Project life. It was assumed that the dust suppression water demand may be obtained from sources of lower water quality (via the Process Water Tank), such as harvested surface runoff and groundwater collected in-pit.

Table 6.3 – Dust suppression demand

Project year

Area requiring dust suppression (ha) Total dust

suppression demand (kL/d)

Estimated annual average dust suppression

demand (ML/yr) Mining

Pit

Waste rock dump

Haul roads / access roads

EOY0 to EOY4 16.2 33.4 41.6 3,605 1,317 EOY4 to EOY5 25.3 50.8 41.6 4,324 1,566 EOY5 to EOY6 25.3 44.1 41.6 4,142 1,513 EOY6 to EOY7 25.3 37.4 41.6 3,961 1,447 EOY7 to EOY8 25.3 30.8 41.6 3,779 1,380 EOY8 to EOY10 25.3 15.4 41.6 3,361 1,228

6.8.4 Underground mining equipment demands

A maximum nominal underground mining demand rate of 100 kL/d was adopted when all three underground mines (Rockface, Bellbird and Reward) are operating. That is, the adopted underground mine demand is 33.3 kL/d for each operating underground mine. Table 6.4 shows the adopted underground mine demand rates over the Project life. It is assumed that underground mining equipment demands can be supplied from raw water (plant standard), mine affected water and sediment laden water if necessary. If insufficient water is available from the above sources, raw water (potable standard) will be used.



Table 6.4 – Underground mining demand

Project year

Marshall / Reward

operations

Bellbird operations

Rockface operations

Underground mine demand

(kL/d)


(ML/yr)

EOY0 to EOY4 open cut only none underground only 33.3 12.2

EOY4 to EOY5 open cut + underground

open cut only

underground only 66.7 24.3

EOY5 to EOY6 underground only

open cut only



open cut + underground



open cut + underground none 66.7 24.3


underground only none 66.7 24.3

6.9 MANAGEMENT OF EXISTING MINE DISTURBANCE AREAS

6.9.1 Process plant and ROM pad

The existing process plant equipment will be removed. The existing ROM pad may be reused as part of the new process plant.

Runoff from the existing process plant and ROM pad will drain to the proposed process water dam, and be reused to satisfy site demands.

6.9.2 Tailing dams

The larger existing tailings dam will be incorporated into the construction of the new tailings storage facility. The smaller tailings dam near the process plant will likely remain in place. Runoff that collects in the smaller tailing storage dam will eventually report to the process water dam, and be reused to satisfy site demands.

6.9.3 Waste rock dump

The existing waste rock dump will be removed, with the waste rock placed in the Reward or Bellbird waste rock dumps, or replaced in the existing Marshall Reward open cut pit.

6.9.4 Existing Green Parrot open cut pit

The existing Green Parrot open cut pit will remain as per existing conditions. Runoff from the pit catchment will continue to collect in the floor of the pit and evaporate or seep into the underlying rock.



7 Water balance modelling

7.1 OVERVIEW The performance of the water management system (WMS) was assessed using the OPSIM water balance model. OPSIM is a computer-based operational simulation model that has been developed to assess the dynamics of the water balance under varying rainfall and catchment conditions throughout the development of the Project.

The OPSIM model dynamically simulates the operation of the WMS and keeps complete account of all site water volumes and representative water quality on a daily time step. Full details of the configuration and calibration of the Jervois OPSIM model, including input assumptions, are provided in Appendix B.

The Jervois OPSIM model was used to predict the performance of the following:

• Overall water balance - the average inflows and outflows of the WMS for a number of representative realisations (Section 7.3.1);

• Mine water inventory – the risk of accumulation of water in the mining pits and underground mines and the Process Water Dam (Section 7.3.2);

• External water demand – the risk and associated volumes of requiring imported external water (via the bore fields) to supplement mine site water demands (Section 7.3.3); and

• Uncontrolled releases (spillway discharges) – the risk of uncontrolled releases from the surface water storages to the receiving environment (Section 7.3.4).

Long-term static simulations of the water balance model were made to assess the impacts of the upgraded Jervois Dam on lake water levels and Unca Creek streamflow (129 year simulation period), as well as the behaviour of the final voids (500 year simulation period). The configuration of these static simulations is described in Appendix B.

7.2 INTERPRETATION OF RESULTS In interpreting the results of the water balance assessment (excluding the results of the long-term static simulations described above), it should be noted that the results provide a statistical analysis of the water management system’s performance over the 10 years of mine life, based on 119 realisations with different climatic sequences.

The model results are presented as a probability of exceedance. For example, the 10th percentile represents 10% probability of exceedance and the 90th percentile results represent 90% probability of exceedance. There is an 80% chance that the result will lie between the 10th and 90th percentile traces.

Whether a percentile trace corresponds to wet or dry conditions depends upon the parameter being considered. For site water storage, where the risk is that available storage capacity will be exceeded, the lower percentiles correspond to wet conditions. For example, there is only a small chance that the one percentile storage volume will be exceeded, which would generally correspond to wet conditions.

For external site water supply volumes (for example), where the risk is that insufficient water will be available, there is only a small chance that more than the one percentile water supply volume would be required. This would generally correspond to dry climatic conditions.

It is important to note that a percentile trace shows the likelihood of a particular value on each day and does not represent continuous results from a single model realisation. For example, the 50th percentile trace does not represent the model time series for median climatic conditions.



7.3 WATER BALANCE MODEL RESULTS

7.3.1 Overall water balance

Water balance results for all of the 119 modelled realisations are presented in Table 7.1, annually averaged over each mine stage. The results presented in Table 7.1 are the average of all realisations and will include wet and dry periods distributed throughout the mine life. Rainfall yield for each mine stage is affected by the variation in climatic conditions within the adopted climate sequence.

Table 7.1 provides an indication of the long-term average annual inflows and outflows. Key outcomes from the overall water balance are as follows:

• There is no accumulation of water predicted during the first six years of mining (EOY0 to EOY6) as the total water supply is equal to or exceeded by the total site demand. As groundwater inflows into the underground mines increase, water accumulation is predicted to begin to occur in year 6, increasing towards the end of Project life).

• Groundwater inflows into the underground mines continuously increase until they peak during EOY6 to EOY7 when all three underground mines are operating simultaneously. From EOY7, groundwater inflows gradually decrease towards the end of the Project in EOY10.

• The average external water supply requirements vary over the life of the Project. The following is of note:

o External water supply requirement is largest at the start of the Project (EOY0), reducing significantly towards EOY6 in conjunction with the increasing availability of groundwater from the underground mines to meet site demands. External water supply increases from EOY6 to EOY10 as groundwater inflows to the underground mines decrease from EOY6 to EOY10.

o The average annual raw water supply requirements from Jervois Dam varies between 1 and 174 ML/yr over the life of the Project.

o The average annual external raw water supply requirements from the groundwater bore fields varies between 20 and 1,353 ML/yr over the life of the Project.

• There were no modelled uncontrolled releases (spillway overflows) from the Process Water Dam over the life of the Project.

• There are minor uncontrolled releases (spillway overflows) from the sediment dams (about 3 ML/yr) during EOY0 to EOY4. The predicted uncontrolled releases are larger from EOY4 towards the end of the mine life as water stored in the sediment dams is no longer pumped back to the mine water management system. The water balance model does not account for the potential controlled release of water from the waste rock sediment dams. The average annual volume of sediment dam uncontrolled releases varies between 8.0 and 9.8 ML/yr from EOY4 to the end of the mine life (EOY10).



Table 7.1 – Annual site water balance (average annual volumes)

Component Process Volume (ML/yr)

EOY0 to EOY4

EOY4 to EOY5

EOY5 to EOY6

EOY6 to EOY7

EOY7 to EOY8

EOY8 to EOY10

Inflows Rainfall runoff (excluding Jervois Dam) 46 65 66 68 65 66

Dewatered Groundwater inflows 669 1,384 2,188 2,366 1,711 1,469

Supply from Jervois Dam 169 174 41 1 143 164 Supply from bore field 1,353 908 175 20 378 681

Total 2,237 2,531 2,471 2,454 2,297 2,380

Outflows Evaporation (excluding Jervois Dam) 102 112 117 123 116 115

Process Plant demand 761 761 761 761 761 761 Dust suppression 1,328 1,592 1,526 1,459 1,392 1,238 Underground mine demand 12 25 25 37 25 24 Potable water demand 34 34 34 34 34 34

Releases from Sediment Dams 3.0 8.0 9.4 9.8 9.6 9.6

Releases from Process Water Dam 0.0 0.0 0.0 0.0 0.0 0.0

Total 2,239 2,531 2,472 2,424 2,337 2,182

Change in Site Water Inventory -2 -1 -1 30 -40 198

7.3.2 Mine site storage inventory

7.3.2.1 Process Water Dam

Figure 8.23 shows the percentile plots of stored inventory in the Process Water Dam (PWD) over the 10-year simulation period. The PWD is the primary water storage of mine-affected water on site. Although the capacity of the PWD is 183 ML, the maximum operating storage level of the PWD is set at 95 ML (i.e. any pumping operation to the PWD stops when the volume in the dam is above 95 ML). This will provide a sufficient storage buffer in the PWD to prevent uncontrolled spills during heavy rainfall.

As most site demands are supplied via the PWD, a minimum operating storage level of 9.5 ML was set for the PWD. When the storage level in the PWD drops below 9.5 ML, water is pumped from the raw water system (Jervois Dam and the groundwater bore fields) to the PWD until the minimum operating storage level is restored.

The following is of note:

• The PWD does not empty over the simulation period due to the supply of water from Jervois Dam and the groundwater bore fields, maintaining the minimum operating storage level in the dam (9.5 ML);

• There is a 1% chance that the volume in the PWD will exceed the maximum operating storage level (95 ML).

• The maximum predicted volume in the PWD based on all simulated realisations is 176 ML, which is 9 ML less than the full supply level (183 ML).



Figure 7.1 – Process Water Dam stored inventory

7.3.2.2 Jervois Dam

Figure 8.23 shows the percentile plots of stored inventory in Jervois Dam over the 10-year simulation period. Jervois Dam is the primary source of raw water (potable standard) and secondary source of raw water (plant standard) for the site. A minimum operating storage level of 47 ML (15% capacity) has been adopted to prevent the dam from emptying.

Figure 7.2 – Jervois Dam stored inventory

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7.3.2.3 Open cut pits and underground mines

Figure 7.3, Figure 7.4 and Figure 7.5 show the percentile plots of stored inventory in the Reward, Bellbird South and Bellbird North open cut pits respectively. Figure 7.6, Figure 7.7 and Figure 7.8 show the percentile plots of stored inventory in the Rockface, Reward and Bellbird underground mines respectively. Figure 7.9 shows the percentile plots of stored inventory in the existing void (south of the Reward Pit).

The inundation characteristics in the open cut pits and the underground mines provide an indication as to whether there is sufficient pumping (dewatering) infrastructure and storage volume to prevent operational problems. The following is of note:

• There is a relatively low risk of accumulating significant volumes of water in the open cut pits and the underground mines over the life of the Project.

• During the operating phase of the open cut pits:

o There is a 10% chance of accumulating more than 8.5 ML in the Reward Pit, 1.5 ML in Bellbird South Pit and 0 ML in the Bellbird North Pit.

o There is a 1% chance of accumulating up to 85 ML in the Reward Pit, 42 ML in the Bellbird South Pit and 9 ML in the Bellbird North Pit.

• In the Rockface Underground Mine, there is less than 1% chance of accumulating more than 3 ML of water during the operating phase of the mine (from EOY0 to EOY7). Water accumulates after EOY7 when mining ceases and the underground mine is no longer dewatered.

• In the Reward Underground Mine, there is a 10% chance of accumulating more than 4 ML of water over the life of the Project. There is also a 1% chance of accumulating up to 150 ML between EOY5 and EOY7.

• In the Bellbird Underground Mine, there is a 10% chance of accumulating more than 2 ML of water over the life of the Project. There is also a 1% chance of accumulating up to 190 ML between EOY6 and EOY8.

• In the existing Marshall Reward pit, there is less than 1% chance of the full supply storage level (30 ML) being exceeded.

Figure 7.3 – Reward Open Cut Pit stored inventory

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Figure 7.4 – Bellbird South Open Cut Pit stored inventory

Figure 7.5 – Bellbird North Open Cut Pit stored inventory

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Figure 7.6 – Rockface Underground Mine stored inventory

Figure 7.7 – Reward Underground Mine stored inventory

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Figure 7.8 – Bellbird Underground Mine stored inventory

Figure 7.9 – Existing Marshall Reward pit stored inventory

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7.3.3 External water demand

Figure 7.10 and Table 7.2 shows the total (combined) annual modelled demand for raw water from Jervois Dam and the groundwater bore fields over the Project life. The results indicate the following:

• External water supply is required in all years to satisfy demand;

• The peak annual demand for external raw water occurs in year 1 of project life, and ranges between 1,856 ML/year and 2,086 ML/year;

• Demand for external raw water decreases rapidly to less than 100 ML/year by year 7 of project life (due to increased groundwater inflows);

• It should be noted that the predicted demand includes significant dust suppression demand. During the first four years of the Project life it may be possible to rationalise dust suppression demands to reduce the amount of external water imported to the site.

Figure 7.10 – Annual external water requirements

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Table 7.2 – Annual external water requirements

Project year

Total raw water requirement from external sources (ML/a)

1% chance of requiring





1 2,086 2,080 2,065 2,006 1,856 2 1,797 1,791 1,773 1,715 1,568 3 1,291 1,286 1,268 1,210 1,089 4 1,034 1,029 1,010 949 716 5 1,118 1,112 1,091 1,037 801 6 264 259 238 189 70 7 42 41 38 35 33 8 597 585 555 432 146 9 824 818 800 743 514 10 943 937 919 855 634

7.3.4 Uncontrolled releases (spillway overflows)

The water balance model was used to investigate the potential frequency and volume of uncontrolled releases (spillway overflows) from the process water dam and the waste rock dump sediment dams. The following is of note with regards to predicted uncontrolled releases:

• No uncontrolled releases of mine affected water are predicted to occur from the process water dam in any year of Project life;

• Uncontrolled releases of sediment laden water from the waste rock sediment dams have the potential to occur in all years of the Project life:

o During years 1 to 4 of Project life, there is a 10% chance of minor uncontrolled releases (less than 5 ML in any year) of sediment laden water from the waste rock dump sediment dams.

o There is a 1 % chance of up to 80 ML of uncontrolled releases occurring in years 3 and 4 of Project life.

o Uncontrolled releases from the waste rock sediment dams are predicted to increase from year 5 of Project life onwards as the runoff captured in the dams is no longer pumped back to the mine water management system;

o The water balance model does not account for the potential controlled release of water that may occur from the waste rock sediment dams from year 5 of Project life onwards (pending suitable water quality monitoring outcomes). If controlled releases of water are made from the sediment dams following runoff events (as per best practice operation of sediment dams), the frequency and volume of uncontrolled releases from year 5 onwards would be reduced significantly.



Table 7.3 – Annual total volume of overflows from the sediment dams

Project Year

Volume of overflows (ML/yr) 1%

probability 10%

probability 50%

probability 1 57.4 2.3 0.0

2 72.9 2.3 0.0

3 80.2 3.1 0.0

4 80.2 4.5 0.0

5 172.8 13.0 0.0

6 172.8 16.9 0.0

7 196.4 21.7 0.0

8 172.8 21.6 0.0

9 172.8 21.7 0.0

10 172.8 21.7 0.0

7.4 FINAL VOID BEHAVIOUR The water balance model was used to investigate the long-term behaviour water levels in of the final voids at the project site following mine closure. The final void water balance model uses a synthetic 500-year climate sequence that has been created by looping the 129 years of available data. Therefore, there are climatic events (wet period and dry periods) that are repeated in the 500-year climate sequence used in the final void analysis.

Based on the CloudGMS (2018) predicted groundwater inflows to the open cut pits for the operational period of the mine, it is assumed long term groundwater inflows to the final voids at the Project will be negligible, due to evaporation from the pit surfaces (i.e. the pits will be considered groundwater sinks).

Therefore, the only water that collects in the final voids will be surface water runoff from the pit catchments. This runoff will collect in the base of the pits and evaporate over time. The final landform for the Project will ensure that the remnant surface water catchments that drain into the final voids are limited to the voids themselves.

The final void water balance model indicates the following:

• All voids will typically have a small volume of surface water runoff stored in the base of the void.

• The stored water depth in each void is predicted to typically vary between 10 m and 15 m deep, however this may increase to as much as 30 m deep during extended wet periods.

• The water surfaces in the final voids are generally between 40 m and 100 m below surrounding ground levels.



Figure 7.11 – Final void water levels – Reward Void

Figure 7.12 – Final void water levels – Bellbird South Void

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Figure 7.13 – Final void water levels – Bellbird North Void

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8 Flood modelling assessment

8.1 OVERVIEW A Unified River Basin Simulator (URBS) hydrological model (Carroll, 2016) and a TUFLOW two-dimensional hydraulic model (WBM, 2017) were developed to simulate the flood behaviour of Unca Creek and its tributaries in the vicinity of the Project.

No data is available to calibrate the URBS and TUFLOW models. Therefore, the models were developed in accordance with the 2016 Australian Rainfall and Runoff guideline (AR&R 2016) (Ball et al, 2016). Descriptions of the model development are given in Appendix C.

The models were used to estimate peak flood levels, depths and extents in the vicinity of the Project for the 10% and 1% AEP and the probable maximum flood (PMF) events under existing conditions (pre-mining), operational conditions (during mining) and final landform conditions (post-mining). It should be noted that all design event modelling undertaken assumes that Jervois Dam is full to the spillway level at the onset of the event.

The model results for the 10% and 1% AEP events were used to assess the flood impacts of the Project. The model results for the 0.1% AEP event were used to size the proposed Unca Creek diversion and the crest heights of proposed flood protection bunds under operational mining conditions. The model results for the PMF event were used to assess the immunity of the final void under the final landform conditions.

8.2 EXISTING CONDITIONS FLOODING Figure 8.1 and Figure 8.2 show the peak flood levels, depths and extents across the entire Project area for the 10% AEP and 1% AEP events under existing (pre-mine) conditions. Figure 8.3 and Figure 8.6 show the existing conditions peak flood depths and velocities respectively in the vicinity of the Reward Pit and Process Plant area. Figure 8.4 and Figure 8.5 show the corresponding peak flood velocities for the 10% and 1% AEP events.

The model results indicate that the proposed infrastructure for the Project are generally located outside of the 1% AEP flood extent except for the proposed Reward Pit, which traverses the Unca Creek channel and floodplain. The proposed Reward and Bellbird waste rock dumps appear to be located across existing overland flow paths, however the dumps will not be affected by flooding from Unca Creek and the Unca Creek tributary. Clean and dirty water diversion drains will be used to manage overland flows around the waste rock dumps.



Figure 8.1 – Peak flood depths and extents, existing conditions, 10% AEP (10 year ARI) event



Figure 8.2 – Peak flood depths and extents across the entire Project area, existing conditions, 1% AEP (100 year ARI) event



Figure 8.3 – Peak flood depths and extents near the Reward Pit and Process Plant area, existing conditions, 1% AEP (100 year ARI) event



Figure 8.4 – Peak flood velocities across the entire Project area, existing conditions, 10% AEP (10 year ARI) event



Figure 8.5 – Peak flood velocities across the entire Project area, existing conditions, 1% AEP (100 year ARI) event



Figure 8.6 – Peak flood velocities near the Reward Pit and Process Plant area, existing conditions, 1% AEP (100 year ARI) event



8.3 OPERATIONAL CONDITIONS FLOODING

8.3.1 Overview

The existing conditions URBS and TUFLOW models were modified to reflect operational conditions. The following changes are proposed between the existing conditions and the operational conditions:

• The Jervois Dam spillway will be raised and widened. This will change the behaviour of spills from the dam and affect design discharges in Unca Creek upstream of the Reward operational area. The URBS hydrologic model was modified to incorporate the raised dam spillway. The updated URBS model was then used to derive updated design discharge hydrographs for the TUFLOW model.

• The proposed Unca Creek diversion will divert all Unca Creek flows around the proposed Reward Pit for all evens up to and including the 0.1% AEP event. The TUFLOW hydraulic model was modified to incorporate this diversion. Descriptions of the proposed Unca Creek diversion are provided in Section 8.4.

8.3.2 Operational conditions peak flood levels, depths and extents

Figure 8.7 and Figure 8.8 show the peak flood levels, depths and extents across the entire Project area for the 10% AEP and 1% AEP events under operational conditions. Figure 8.10 and Figure 8.11 show the corresponding peak flood velocities for the 10% and 1% AEP events. Figure 8.9 and Figure 8.12 show the operational conditions peak flood depths and velocities respectively in the vicinity of the Reward Pit and Process Plant area.

8.3.3 Operational conditions flood impacts

Figure 8.13 and Figure 8.14 show the predicted increases in peak flood levels across the Project area for the 10% AEP and 1% AEP events respectively under operational conditions. Figure 8.15 and Figure 8.16 show the predicted increases in peak flood velocities across the Project area for the 10% AEP and 1% AEP events respectively under operational conditions. The predicted impacts of the Project are summarised below:

• There are no predicted increases in peak flood levels and velocities along the watercourses traversing the Project area, except in Unca Creek.

• The Jervois Dam spillway will be raised and widened under operational conditions, increasing the peak outflow discharge from the spillway by about 10%, resulting in minor increases in peak flood levels and velocities along Unca Creek downstream of Jervois Dam.

• Increases in peak flood levels of up to 0.1 m are predicted in Unca Creek downstream of Jervois Dam for the 10% AEP and 1% AEP events. The average increase in flood levels along Unca Creek is about 0.05 m for the 10% AEP event and about 0.08 m for the 1% AEP event. These increased flood levels are not expected to have any material impact on existing land uses downstream of the Project area.

• There are minor predicted increases in peak velocities of up to 0.2 m/s in Unca Creek downstream of Jervois Dam for the 10% AEP and 1% AEP events. The average increase in peak velocities along Unca Creek is about 0.07 m/s for the 10% AEP event and about 0.11 m/s for the 1% AEP event. Given that the average peak flood velocities along Unca Creek under existing conditions are about 0.9 m/s for the 10% AEP event and 1.3 m/s for the 1% AEP event, the minor predicted increases in peak velocities due to the Project are not considered significant.

• If Jervois Dam was removed (the pre dam case), the 1% AEP peak discharge in Unca Creek downstream of the dam sit would be approximately 58.4 m3/s. The 1% AEP peak discharge downstream of the existing dam is 27.6 m3/s, and this will increase to 35.1 m3/s after the dam is upgraded. Therefore, the predicted increase in flood levels and velocities following the dam upgrade would be closer to the pre dam flooding conditions.



Figure 8.7 – Peak flood depths and extents across the entire Project area, operational conditions, 10% AEP (10 year ARI) event



Figure 8.13 – Predicted increases in peak flood levels under operational conditions, 10% AEP (10 year ARI) event



Figure 8.14 – Predicted increases in peak flood levels under operational conditions, 1% AEP (100 year ARI) event



Figure 8.15 – Predicted increases in peak flood velocities under operational conditions, 10% AEP (10 year ARI) event



Figure 8.16 – Predicted increases in peak flood velocities under operational conditions, 1% AEP (100 year ARI) event



8.4 UNCA CREEK DIVERSION

8.4.1 Overview

The proposed Reward Pit traverses the existing Unca Creek channel and floodplain. It is proposed to divert Unca Creek around the northern side of the proposed Reward Pit as part of the Project. The proposed diversion will ensure that the Reward Pit is protected from flows from the upstream catchment (including overflows from Jervois Dam) for events up to and including 0.1% AEP (1,000 year ARI) during the operational phase of the mine.

The proposed Unca Creek diversion was designed as an operational structure. It is of note that NT EPA will require that the final voids are protected from floodwater for events up to the PMF, which is an event significantly larger than 0.1% AEP. The proposed flood mitigation measures for the final landform is described in Section 8.5.

8.4.2 Diversion channel configuration

Figure 8.17 shows the conceptual alignment and extent of the proposed Unca Creek diversion. Figure 8.18 shows the longitudinal profile along the proposed diversion alignment. Note that chainage zero on Figure 8.18 is about 300 m upstream of the proposed diversion. Figure 8.19 compares channel cross sections at four locations (chainages) along the proposed diversion (refer to Figure 8.17 and Figure 8.18 for cross section locations). Table 8.1 summarises the channel characteristics of the proposed diversion.

The proposed diversion was designed as a trapezoidal channel with a base width of 30 m and batter slopes of 1V:5H. The diversion was sized to convey the 0.1% AEP discharge from the catchment upstream of the Reward Pit under operational conditions (incorporating the raised Jervois Dam spillway). The diversion will be deepest (about 9.9 m) at its middle section where it crosses the ridge line north of the Reward Pit. Bunds are also required at several locations along the diversion as shown in Figure 8.17 to prevent water overflowing from the diversion into the pit.

8.4.3 Flood assessment

Figure 8.17 compares the predicted peak flood extents for the 0.1% AEP (1,000 year ARI) event under existing and operational conditions. Figure 8.20 shows longitudinal profiles of predicted peak velocities along the existing Unca Creek alignment under existing conditions for the 10%, 1% and 0.1% AEP events. Figure 8.21 shows a longitudinal profiles predicted peak velocities along the diverted Unca Creek alignment under operational conditions for the 10%, 1% and 0.1% AEP events.

The model results indicate that the proposed diversion and associated bunds will provide the Reward Pit immunity from flooding up to and including the 0.1% (1,000 year ARI) event during the operational phase of the mine.

The average peak velocities along the proposed diversion are predicted to be approximately 0.94 m/s for the 10% AEP event (representative of moderate floods) and 1.48 m/s for the 1% AEP event (representative of a large floods). The predicted peak velocities within the diversion channel are within the upper and lower bounds observed under existing conditions (between 0.5 m/s and 1.5 m/s for the 10% AEP event, and between 1.0 m/s and 2.0 m/s for the 1% AEP event).

On this basis, the proposed diversion channel is expected to perform in a similar manner to the existing Unca Creek channel under flood conditions.



Figure 8.17 – Proposed Unca Creek Diversion, with 0.1% AEP flood extents under existing and operational conditions



Figure 8.18 – Longitudinal profile along the proposed diversion alignment

Table 8.1 – Proposed Unca Creek Diversion channel characteristics

Channel attribute Value

Physical attributes

Length (m) 1,714

Base width (m) 30.00

Maximum top width (m) 184.15

Maximum cut depth (m) 9.86

Batter slope (V:H) 1:5 (20%)

Longitudinal grade (V:H) 1:277 (0.36%)

Upstream invert (mAHD) 347.94

Downstream invert (mAHD) 341.70

Cut volume (m3) 441,613

Hydraulic characteristics

10% AEP mean flood velocity (m/s) 0.94

1% AEP mean flood velocity (m/s) 1.48

0.1% AEP mean flood velocity (m/s) 2.11

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Figure 8.19 – Comparison of channel cross sections at four locations along the proposed Unca Creek Diversion (looking downstream)

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Figure 8.20 – Existing conditions peak flood velocities along the existing Unca Creek alignment, 10%, 1% and 0.1% AEP events

Figure 8.21 – Operational conditions peak flood velocities along the diverted Unca Creek alignment, 10%, 1% and 0.1% AEP events

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8.5 FINAL LANDFORM FLOODING ASSESSMENT Figure 8.22 shows the final landform at the Reward operational area, and the extent of the PMF from Unca Creek. Note that the Bellbird operations are not affected by flooding up to the PMF. The PMF is defined as the largest flood that could conceivably occur at a particular location. Details of the methodology to define the PMF is given in Appendix B.

In absence of a final landform design, the proposed final landform configuration adopted in this flood assessment was based on the final pit and waste rock dump extents from the supplied mine plans.

The proposed Unca Creek diversion (described in Section 8.4) will form part of the final landform. It is also proposed to construct the Eastern and Western flood protection bunds along the right bank of Unca Creek and the Unca Creek Diversion to protect the final void and the TSF from flooding up to the PMF. The bunds will be incorporated into the rehabilitated final landform to form a self-sustaining structure that does not require long term maintenance. Note that the western section of the proposed Western Bund may be formed by raising the northern embankment of the TSF.

Figure 8.23 and Figure 8.24 show the predicted PMF peak flood levels along the proposed Eastern and Western bund alignments respectively. The proposed bunds will have a crest height above the PMF level from Unca Creek. Based on the hydraulic model results, the proposed bunds will have maximum crest heights of about three to four metres above existing ground levels.

It was also assumed that the final Reward waste rock dump extent from the supplied mine plans will be unchanged, and that the dump will be rehabilitated as part of the final landform.



Figure 8.22 – Proposed final landform configuration, with PMF event peak flood levels, depths and extents



Figure 8.23 – Predicted PMF peak flood levels along the proposed Western Bund alignment (west to east)

Figure 8.24 – Predicted PMF peak flood levels along the proposed Eastern Bund alignment (north to south)

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9 Surface water monitoring

9.1 OVERVIEW Monitoring of surface water quality will be ongoing as part of the Project, both for background water quality locations (undisturbed by mining), the surface water storages proposed as part of the project, and in receiving environments downstream of the Project area. Figure 9.1 shows the locations of the proposed water quality monitoring points.

9.2 SURFACE WATER STORAGES The proposed storages at the Project (process water dam, Jervois Dam, underground dewatering dam and waste rock sediment dams) will be monitored at least quarterly (and daily during or following significant runoff events). The proposed suite of monitoring parameters and recommended monitoring frequency is given in Table 9.1. A significant runoff event is one where the water level in any dam rises by greater than 0.3 m.

Table 9.1 – Surface water storage monitoring parameters and frequencies

Parameter Frequency

Water level / storage volume Daily

Non-metallic indicators

pH Quarterly / daily during significant runoff events

Electrical conductivity Quarterly / daily during significant runoff events

Total dissolved solids Quarterly / daily during significant runoff events

Turbidity Quarterly / daily during significant runoff events

Dissolved oxygen Quarterly / daily during significant runoff events

Sulphate Quarterly / daily during significant runoff events

Nitrate Quarterly / daily during significant runoff events

Metals and metalloids (filtered, unless otherwise stated)

Aluminium Quarterly / daily during significant runoff events

Arsenic Quarterly / daily during significant runoff events

Cadmium Quarterly / daily during significant runoff events

Copper Quarterly / daily during significant runoff events

Iron Quarterly / daily during significant runoff events

Lead Quarterly / daily during significant runoff events

Magnesium Quarterly / daily during significant runoff events

Manganese Quarterly / daily during significant runoff events

Mercury Quarterly / daily during significant runoff events

Nickel Quarterly / daily during significant runoff events

Zinc Quarterly / daily during significant runoff events



Figure 9.1 – Surface water monitoring program



9.3 BACKGROUND SITES AND RECEIVING WATERS Background and receiving water monitoring will continue to take place following runoff events at the existing monitoring locations specified in Table 9.2. The background and receiving water monitoring parameters will be as per those specified for surface water storages in Table 9.1.

Table 9.2 – Background and receiving water monitoring locations

Location Background / receiving water Comments

JSW01 Receiving water Downstream boundary of Project on Unca Creek tributary. Includes Bellbird and Rockface mining disturbance area.

JSW02 Background Unca Creek upstream of diversion. No mining disturbance in catchment.

JSW04 Background Drainage feature in catchment of Unca Creek tributary. No mining disturbance in catchment.

JSW05 Background Drainage feature in catchment of Unca Creek tributary. No mining disturbance in catchment.

JSW06 Background Unca Creek downstream of Jervois Dam. No mining disturbance in catchment.

JSW07 Receiving water Drainage feature in catchment of Unca Creek tributary. Includes Bellbird mining disturbance area.

JSW09 Receiving water Downstream of Project at confluence of Unca Creek and Unca Creek tributary. Includes all mining disturbance area.

JSW10 Receiving water Downstream boundary of Project on Unca Creek. Includes Reward mining disturbance area.



10 Potential impacts and proposed mitigation measures

10.1 CHANGES TO STREAMFLOW IN UNCA CREEK

10.1.1 Potential impacts

The proposed upgrade to Jervois Dam will potentially result in changes to the existing conditions streamflow regime in Unca Creek. The upgraded dam will require a greater volume of catchment runoff to fill the dam before the spillway is activated and flow leaves the dam. Further, the dam will be relied upon as a source of raw water, particularly during the first four years of operations (before groundwater inflows to the underground increase). Therefore, the volume of water stored in the dam will be drawn down after a runoff event more rapidly than under existing conditions.

Overall, the proposed upgrade to the dam will potentially reduce the magnitude and number of overflows from the dam, particularly in the first four years of mine life.

The water balance model was used to assess the change in flows in Unca Creek immediately downstream of the dam following the upgrade. Figure 10.1 shows the existing conditions and predicted post-upgrade (for year 1 of project life and post-mine closure) flow duration curves for Unca Creek immediately downstream of the dam for the first four years of Project life. The following is of note:

• Under existing conditions, Jervois Dam is predicted to overflow via the spillway on approximately 0.8% of all days. That is, there is no flow over the spillway 99.2 % of the time;

• Under year 1 conditions (upgraded dam and site demands sourced from the dam), the dam is predicted to overflow only 0.1% of the time. That is, there would be no flow over the spillway for 99.9 % of the time.

• Under the post mine closure scenario (upgraded dam and no site demands), the dam is predicted to overflow about 0.15 % of the time. That is, there would be no flow over the spillway for 99.85 % of the time.

• The maximum predicted daily flow over the spillway is increased by about 500 ML/day for both of the upgraded dam cases due to the more efficient and larger spillway proposed as part of the upgrade.

It should be noted that the existing dam has already altered the streamflow regime of Unca Creek significantly. Further, the dam is situated in an arid catchment, where it would not be unusual for the dam not to overflow for several years. Water balance modelling indicates that the existing dam on average only overflows in every fourth year. The upgraded dam is predicted to overflow on average every 11 years under the year 1 scenario, and every 9 years under the post-mine closure scenario.

Therefore, the proposed dam upgrades will alter the streamflow regime in Unca Creek downstream of the dam, with reduced frequency of spill events, but increased maximum spill rates. The change in streamflow regime will have a significant affect along the reach of Unca Creek within the Project, up until the Unca Creek tributary confluence which doubles the Unca Creek catchment. The impacts downstream of this point will be insignificant.



Figure 10.1 – Impact of upgraded Jervois Dam on Unca Creek flows

10.1.2 Proposed mitigation

No mitigation measures are proposed as the potential impacts of the upgraded dam on Unca Creek streamflow are insignificant.

10.2 INCREASE IN JERVOIS DAM LAKE EXTENT


The proposed repairs and upgrade to Jervois Dam (increased spillway level) will result in an increase in the area inundated by the lake behind the dam wall. The water balance model was used to investigate the impact of the dam upgrade on lake water levels. Figure 10.2 shows the extent of inundation from the lake at full supply level under both existing conditions and post-mining conditions. The area of inundation at full supply will increase from about 16 ha under existing conditions to about 36 ha under the upgraded dam case. The increased inundation extent does not affect any existing structures or sensitive environmental or cultural heritage areas.

Figure 10.3 shows the water level duration curves for the lake under existing conditions and post mine closure (when lake levels will be highest). The proposed dam upgrade will result in an increase to the frequency of inundation. The water balance model predicts that water levels in the upgraded dam will exceed the existing full supply level approximately 27 % of the time (and conversely will be below the existing full supply level 63 % of time).


No mitigation measures are proposed as the potential impacts of the increased inundation extent and frequency are not considered to be significant. However, the mine closure plan for Jervois Dam could include the upgraded dam remaining in place, reduction in spillway level to the pre-mining level, or complete removal of the dam, depending on whether maintaining the dam is beneficial to the post-mining landholder.



Figure 10.2 – Impact of upgraded Jervois Dam on inundation extent at full supply level



Figure 10.3 – Impact of upgraded Jervois Dam on inundation frequency

10.3 IMPACTS ON FLOODING


The predicted impacts of the Project are summarised below:

• There are no predicted increases in peak flood levels and velocities along the watercourses traversing the Project area, except in Unca Creek.

• The Jervois Dam spillway will be raised and widened under operational conditions. This has the effect of increasing the peak outflow discharge from the spillway by about 10%. In turn, the increased discharges from the dam spillway results in minor increases in peak flood levels and velocities along Unca Creek downstream of Jervois Dam.

• There are minor predicted increases in peak flood levels of up to 0.1 m in Unca Creek downstream of Jervois Dam for the 10% AEP and 1% AEP events. The average increase in flood levels along Unca Creek is about 0.05 m for the 10% AEP event and about 0.08 m for the 1% AEP event. These minor increases in peak flood levels are not expected to have any material impact on existing land uses downstream of the Project area.

• There are minor predicted increases in peak velocities of up to 0.2 m/s in Unca Creek downstream of Jervois Dam for the 10% AEP and 1% AEP events. The average increase in peak velocities along Unca Creek is about 0.07 m/s for the 10% AEP event and about 0.11 m/s for the 1% AEP event. Given that the average peak flood velocities along Unca Creek under existing conditions are about 0.9 m/s for the 10% AEP event and 1.3 m/s for the 1% AEP event, the minor predicted increases in peak velocities due to the Project are not considered significant.

The relatively minor increases in peak flood levels and velocities in Unca Creek due to the upgrade to Jervois Dam are not considered significant. The increased flood levels and velocities are typically confined to the Unca Creek channel and do not affect any existing structures or property. The peak flood levels, discharges and velocities in Unca Creek with the upgraded dam in place will also be below the ‘pre- dam’ scenario.




The project will not have any significant impact on flooding. No mitigation measures are proposed.

10.4 IMPACTS ON WATER QUALITY


The Project has the potential to impact on water quality in Unca Creek and its tributaries due to controlled and uncontrolled releases of water.

The water balance model has been used to investigate the predicted frequency and volume of uncontrolled releases (spills) of water from the process water dam and waste rock dump sediment dams.

The results of the water balance model show that no uncontrolled releases are predicted from the process water dam in any of the water balance model simulations. Therefore, the Project will not release any mine affected water or dewatered groundwater to the environment.

The water balance model indicates that there is approximately a 10% chance of uncontrolled releases of water from the waste rock sediment dams in the first four years of Project life.

The water balance model predicts an increase in uncontrolled releases from the sediment dams beyond year 4 of Project life, as groundwater inflows increase and water captured in the sediment dams is no longer pumped back to the WMS. The water balance model does not consider the potential for controlled releases of water from the waste rock sediment dam from year 5 onwards (pending suitable water quality), which would reduce the amount of uncontrolled releases.

The following key points are of note with regards to the predicted uncontrolled releases from the waste rock sediment dams:

• The sediment dams are designed to allow TSS and associated metalloids to drop out of suspension and therefore any overflowing water would likely achieve the WQOs.

• Uncontrolled releases of water from the waste rock sediment dams would only occur following significant runoff events. The sediment dams are sized to capture all runoff from the dumps during a 10% AEP 24-hour rainfall event. There is likely to be some flow in the receiving watercourses during rainfall events exceed this design threshold. Therefore, any uncontrolled releases from the sediment dams would be diluted in undisturbed runoff before reaching the downstream boundary of the Project.

• The material placed in the waste rock dumps and the proposed dump construction methods will ensure that runoff from the dumps is generally of similar quality to background runoff from undisturbed catchments within the project site, and will not contain acid rock drainage or significantly elevated concentrations of metalloids (beyond background values).

Therefore, it is considered that the predicted uncontrolled releases from the waste rock sediment dam are unlikely to have any impact of significance on water quality in Unca Creek, as they will occur when there is likely to be some flow in the receiving watercourses, and the uncontrolled releases are likely to be of similar quality to background water quality.


Controlled releases of water will only take place from the waste rock dump sediment dams after year 4 of Project life, provided the quality of runoff from the waste rock dumps has been proven to be equal to or better than background water quality in undisturbed drainage features within the Project area, or the adopted WQOs given in Table 4.1. No



controlled releases of water to the receiving environment are proposed from the process water dam.

10.5 IMPACT OF FINAL VOIDS ON SURFACE WATER


The water balance model was used to assess the long-term behaviour of the final voids at the Project (post mine closure).

It has been assumed that long term groundwater inflows to the final voids at the Project will be negligible, due to evaporation from the pit surfaces (i.e. the pits will be considered groundwater sinks).

The final landform hydraulic modelling has demonstrated that the final voids will be protected from flooding from Unca Creek and its tributaries for all events up to and including the PMF.

Therefore, the only water that collects in the final voids will be surface water runoff from the pit catchments. This runoff will collect in the base of the pits and evaporate over time. The final landform for the Project will ensure that the remnant surface water catchments that drain into the final voids are limited to the voids themselves.

Therefore, the final voids will have no significant impact on surface water.


The proposed final landform ensures that the only water that collects in the final voids will be surface water runoff from the pit catchments.

The final landform also provides the final voids with immunity from flooding for events up to and including the PMF.



11 References

Ball et al, 2016 Ball J, Babister M, Nathan R, Weeks W, Weinmann E, Retallick M, Testoni I (Editors), 2016, Australian Rainfall and Runoff: A Guide to Flood Estimation, Commonwealth of Australia

BMT WBM, 2018 BMT WBM Pty Ltd 2018, TUFLOW User Manual – GIS Based 1D/2D Hydrodynamic Modelling, Brisbane QLD.

BOM, 2005 Commonwealth Bureau of Meteorology, September 2005, Guidebook to the Estimation of Probable Maximum Precipitation: Generalised Tropical Storm Method, Hydrometeorological Advisory Service.

Carrol, 2016 ‘URBS A Rainfall Runoff Routing Model for Flood Forecasting & Design’, D.G. Carroll, Version 6.00, December 2016.

CloudGMS, 2018 FINAL REFERENCE REQUIRED

EGI, 2018 FINAL REFERENCE REQUIRED

Geoscience Australia, 2017

AR&R Data Hub (software), Geoscience Australia, Version 2017_v2, 2017, <http://data.arr-software.org/>.

Jordan, 2005 Jordan P, Nathan R, Mittiga L and Taylor B, 2005, Growth Curves and Temporal Patterns for Application to Short Duration Extreme Events, Aust J Water Resource Volume 9(1), pp.69-80.

Low Ecological, 2018

Low Ecological, 2018, KGL Resources – EL25429 Jervois Base Metal Project EIS, Flora and Fauna Survey. Low Ecological Services P/L

Sedgman, 2018 Sedgman Pty Limited, 2018, Engineering & Consulting Services Jervois Copper Project Pre-Feasibility Study CapEx & OpEx Report.

WRM, 2015 WRM Water and Environment Pty Ltd, October 2015, Alice Springs Flood Investigation and Floodplain Mapping Study, prepared for the Northern Territory Government Department of Lands, Planning & the Environment.

WRM, 2018a WRM Water and Environment Pty Ltd, September 2018, Draft Jervois Mine Water Management Plan, prepared on behalf of KGL Resources

WRM, 2018b WRM Water and Environment Pty Ltd, September 2018, Draft Jervois Mine Erosion and Sediment Control Plan, prepared on behalf of KGL Resources



– Mining schedules and plans



Figure A.1 – Open cut mining at the Reward Pit at the end of year 1 (EOY1)



Figure A.2 – Open cut mining at the Reward Pit at the end of year 5 (EOY5)



Figure A.3 – Underground mining at the Reward Pit at the end of year 4 (EOY4)



Figure A.4 – Underground mining at the Reward Pit at the end of year 10 (EOY10)



Figure A.5 – Open cut mining at the Bellbird Pit at the end of year 5 (EOY5)



Figure A.6 – Open cut mining at the Bellbird Pit at the end of year 5 (EOY8)



Figure A.7 – Underground mining at the Bellbird Pit at the end of year 7 (EOY10)



Figure A.8 – Underground mining at the Bellbird Pit at the end of year 10 (EOY10)



Figure A.9 – Underground mining at the Rockface Pit at the end of year 1 (EOY1)



Figure A.10 – Underground mining at the Rockface Pit at the end of year 7 (EOY7)



– Mine water balance model configuration

Contents

B1 Introduction ________________________________________________ 127 B2 Survey data and aerial photography ______________________________ 127 B3 Climate data ________________________________________________ 127 B4 Simulation methodology _______________________________________ 129

B4.1 Overview _____________________________________________________ 129 B4.2 Modelled staging of mine plan ___________________________________ 129 B4.3 Proposed simulation methodology ________________________________ 130

Jervois Dam upgrade impact assessment model _______________ 130 Final void model _________________________________________ 131

B5 Mine site water management system _____________________________ 131 B5.1 Catchment and land use classification _____________________________ 131 B5.2 WMS schematic and operating rules _______________________________ 132

B6 Catchment yield (AWBM) parameters _____________________________ 138 B7 OPSIM model calibration _______________________________________ 140

B7.1 Methodology __________________________________________________ 140 B7.2 Calibration results _____________________________________________ 140

B8 Water demands ______________________________________________ 141 B8.1 Processing plant _______________________________________________ 141 B8.2 Dust suppression _______________________________________________ 141 B8.3 Potable water demand __________________________________________ 142 B8.4 Underground mine demand ______________________________________ 142

B9 Water sources _______________________________________________ 143 B9.1 Jervois Dam ___________________________________________________ 143 B9.2 Groundwater bore fields ________________________________________ 143 B9.3 Groundwater inflows to open cut pits and underground mines ________ 143 B9.4 Surface runoff _________________________________________________ 143

B10 Water storage sizing __________________________________________ 144 B10.1 Process Water Dam _______________________________________ 144 B10.2 Sediment dams __________________________________________ 144



B1 Introduction This appendix outlines the development of the OPSIM mine water balance model developed for the Project. The model was used to assess the behaviour of the proposed water management system (WMS). This section presents a summary of the proposed methodology and assumptions for the water balance model for the Project.

B2 Survey data and aerial photography Aerial photography (dated 17 December 2017) and LiDAR ground survey of the Project area were acquired from Nitro Solutions on February 2018. The LiDAR ground survey was used to generate a digital elevation model (DEM) of the Project area. For the purpose of the water balance model, this information is assumed to define current conditions at the Project (e.g. land disturbance, catchment areas, etc.) adequately.

B3 Climate data Long term daily rainfall data at Jervois Station from January 1889 to December 2017 (129 years) was obtained from the Queensland Government DSITIA Patch Point data service. Jervois Station is located about 35 km southwest of the Jervois Project area.

Recorded daily rainfall data at the Jervois Dam gauge (Gauge No. R0070009) were obtained from the Northern Territory (NT) Government water portal for the period between October 1977 and December 2010 (33 years). This gauge is only 2 km from Project area, however, the data includes some periods (up to several months) where data is not available.

Morton’s Lake evaporation (also obtained from DSITIA’s Patch Point data service) has been used to estimate evaporation loss from storages.

For this assessment, a long-term daily rainfall dataset for the Jervois Project was developed by adopting the Patch Point rainfall as the base rainfall data, and then supplementing it with recorded rainfall data from Jervois Dam where available. Recorded rainfall data at Jervois Dam which has been verified (categorised as ‘good’ or ‘good-quality’) replaced the Patch Point rainfall data. However, recorded rainfall data at Jervois Dam which has been classified as ‘poor’ or ‘satisfactory’ were ignored. This approach resulted in a reasonable calibration of the OPSIM model against recorded water levels and volumes at Jervois Dam. The model calibration methodology and results are described in Section B7.

Table B.1 shows the long-term monthly averages of Morton’s evaporation, and compares long-term monthly rainfall averages for the Data Drill, Jervois Dam and the combined (adopted) rainfall data. Figure B.1 compares the annual distribution of average monthly rainfall for the Patch Point data, Jervois Dam data and the combined (adopted) rainfall data as well as Morton’s evaporation.

The evaporation pattern shows that evaporation far exceeds rainfall in all months, with greater evaporation occurring in the latter months of the year. The rainfall patterns show higher monthly rainfall occurring during summer. The rainfall patterns also show that by supplementing the patch Point rainfall data with recorded daily rainfall data at Jervois Dam, the long-term monthly average rainfalls were generally unchanged.



Table B.1 – Long-term average monthly rainfall and evaporation

Month

Patch Point average monthly

Mlake evaporation (mm) (1889 - 2017)

Average monthly rainfall (mm)


(1889 - 2017)

Jervois Dam rainfall

(1977 - 2010)

Combined (adopted) rainfall

(1889 - 2017)

Jan 225.7 37.0 47.0 37.2

Feb 191.6 44.3 47.2 43.7

Mar 182.2 25.7 27.1 25.4

Apr 136.9 12.8 15.6 12.6

May 101.1 13.3 17.0 12.8

Jun 80.7 9.4 6.5 8.8

Jul 90.7 9.7 16.6 9.8

Aug 119.6 5.2 3.1 4.8

Sep 151.9 6.5 9.6 6.4

Oct 189.8 13.2 15.1 12.6

Nov 205.2 18.1 23.1 18.2

Dec 224.2 31.9 36.5 32.1

Figure B.1 – TUFLOW model configuration for the existing Jervois Dam spillway

0

50

100

150

200

250

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Aver

age

mon

thly

rai

nfal

l and

eva

pora

tion

(m

m)

Patch Point Mlake evaporation (129 years)

Patch Point rainfall (129 years)

Jervois Dam rainfall (34 years)

Combined (adopted) rainfall (129 years)



B4 Simulation methodology B4.1 OVERVIEW The computer-based operational simulation model (OPSIM) was be used to assess the behaviour of the mine water balance under varying rainfall and catchment conditions throughout the development of the Project. The OPSIM model dynamically simulates the operation of the proposed water management system (WMS) and keeps complete account of all site water volumes on a daily time step.

The OPSIM model was configured to simulate the operations of all major components of the water management system (WMS). The simulated inflows and outflows included in the model are given in Table B.2.

Table B.2 – Simulated Inflows and Outflows to Mine Water Management System

Inflows Outflows

Direct rainfall on water surface of storages Evaporation from water surface of storages

Catchment runoff Process Plant demand

Groundwater inflow to open cut pits Dust suppression demand

Groundwater inflow to underground mines Underground mining water demand

Raw water supply Mine camp and infrastructure area demand

B4.2 MODELLED STAGING OF MINE PLAN Mine schedules for the Project have been provided for 10 representative Project years, providing a mine life of 10 years. Table B.2 summarises the three key stages of the Project life. The proposed mine sequence is summarised as follows:

• At the start of mining (EOY0):

o Open cut mining will commence at the Reward Pit; and

o Underground mining will commence at the Rockface Pit, and will continue until the end of year 7 (EOY7).

• At the end of year 4 (EOY4):

o underground mining will commence at the Reward Pit, while open cut mining will continue simultaneously until the end of year 5 (EOY5); and

o open cut mining will commence at the Bellbird Pit, and will continue until the end of year 8 (EOY8).

• At the end of year 5 (EOY5), open cut mining will cease at the Reward Pit, while underground mining will continue until the end of year 10 (EOY10).

• At the end of year 6 (EOY6), underground mining will commence at the Bellbird Pit, while open cut mining will continue until the end of year 8 (EOY8).

• At the end of year 7 (EOY7), underground mining will cease at the Rockface Pit.

• At the end of year 8 (EOY7), open cut mining will cease at the Bellbird Pit, while underground mining will continue until the end of year 10 (EOY10).

• At the end of year 10 (EOY10), underground mining will cease at the Reward and Bellbird pits.

The 10 year Project life will be represented in the OPSIM model using six representative mine stages, referred to as Stages EOY0_EOY4, EOY4_EOY5, EOY5_EOY6, EOY6_EOY7, EOY7_EOY8 and EOY8_EOY10 as described in Table B.2.



Table B.3 – Adopted mine stages

Project year

Adopted OPSIM

mine stage

Marshall / Reward operations

Bellbird operations

Rockface operations

EOY0 to EOY4 EOY0_EOY4 open cut only none underground only

EOY4 to EOY5 EOY4_EOY5 open cut + underground open cut only underground only

EOY5 to EOY6 EOY5_EOY6 underground only open cut only underground only

EOY6 to EOY7 EOY6_EOY7 underground only open cut + underground underground only

EOY7 to EOY8 EOY7_EOY8 underground only open cut + underground none

EOY8 to EOY10 EOY8_EOY10 underground only underground only none

B4.3 PROPOSED SIMULATION METHODOLOGY

Forecast model

The proposed simulation methodology is to use the ‘forecast’ simulation type in the OPSIM model. The model run duration will be 10 years, to match the operational phase of the mine life, incorporating the six representative stages of the Project life as described above. The adopted approach of modelling six discrete stages will provide a reasonable representation of site conditions over the 10 year period. The number of discrete mine stages may be reduced or increased once more information is available (such as changes in groundwater inflows and water demand rates) to identify key changes in the water management system.

The forecast simulation allows the model configuration to change over the modelled 10 years by linking the six representative stages, reflecting variations in the water management system over time such as production water demands and groundwater inflows. However, the three representative stages may be split into additional stages if necessary, once additional information such as groundwater inflows and variations in water demands are available to identify key changes to the mine water management system.

The physical layout and site catchment areas of the Jervois Project are shown in Figure 6.3 and Figure 6.4 for the Reward and Bellbird operations respectively. The operational rules are described in Section B5.1.2.

To assess the effects of varying climatic conditions, the forecast model will be run for 118 realisations (with each realisation corresponding to the 10 year mine life), using 129 years of simulated climatic and streamflow data available from January 1889 to December 2017. A different rainfall input sequence is applied to each realisation. The first realisation adopts climatic data from 1889 to 1898, the second from 1890 to 1899 and so on through the 129 years of simulated climatic data. A percentile analysis of the resultant realisations can then be undertaken at user-defined confidence intervals to assess the behaviour of the various storages over extended dry and wet periods, reflecting the full range of climatic conditions experienced in the last 129 years.

Jervois Dam upgrade impact assessment model

To assess the impact of the Jervois Dam upgrade on the streamflow behaviour in Unca Creek, the OPSIM model was over the 129 years of historical data for the following three scenarios:



• Existing dam – no mining: this scenario represents the existing Jervois Dam configuration without any water demands from the Project.

• Upgraded dam – post mine closure: this scenario represents the upgraded Jervois Dam configuration after the cessation of mining activities associated with the Project (i.e. without any water demands).

• Upgraded dam – year 1 Project demands: this scenario represents upgraded Jervois Dam spillway configuration during year 1 of the Project, when the water demand from Jervois Dam is greatest. For this scenario, water is drawn from Jervois Dam to supply Project demands. The water demand for year 1 of the Project is maintained over the entire 129 year simulation.

The model results for each scenario was used to assess the long-term frequency of spills from the Jervois Dam spillway over 129 years. The model results are described in Section 10.1 in the main body of this report.

Final void model

In absence of a mine closure plan, it was assumed that there will be three final voids after mine closure in Project Year 10. The three final voids assessed in this study are the Reward, Bellbird South and Bellbird North Pit Voids.

Water levels in the final voids will vary over time, depending on the prevailing climatic conditions, and the balance between evaporation losses and inflows from rainfall, surface runoff, and groundwater. The OPSIM model was used to assess the likely long term water level behaviour of the final voids. The historical rainfall and evaporation sequences were looped five times to create a long term climate record.

The volume of water in the final void is calculated at each time step as the sum of direct rainfall to the void surface, catchment runoff, and groundwater inflows - less evaporation losses.

The adopted final void configuration was based on the supplied Reward Pit shell for Project Year 5, and the Bellbird South and Bellbird North pit shells for Project Year 8. The following is of note with regards to the catchments draining to the voids:

• For the Reward Void, it was assumed that the catchment draining to the proposed Process Water Dam will report to the Reward Void post-mine closure (refer to Figure B.2).

• For the Bellbird North and Bellbird South voids, the contributing catchment area are assumed to be unchanged from the pit catchment areas in Project Year 8 (refer to Figure B.3).

The model results are described in Section 7.4 in the main body of this report.

B5 Mine site water management system B5.1 CATCHMENT AND LAND USE CLASSIFICATION Catchment areas for the proposed have been determined from Digital Surface Model of the existing Project site and the provided mine schedules. To adequately simulate the site water balance, the mine site catchments were classified as either:

• Natural – representing natural (undisturbed) areas;

• Mining pit – representing the pit floor;

• Waste rock dump – representing compacted dumped overburden material; and

• Hardstand – representing mine infrastructure areas such as haul roads and the process plant area.



Figure B.2 and Figure B.3 show the adopted catchment and land use classifications for the Reward and Bellbird operations respectively. A summary of catchment areas and landuses is provided in Table B.4.

Table B.4 – Storage catchment areas

Storage

Contributing catchment (ha)

Natural/ undisturbed Mining pit Hardstand Waste rock

dump Total

From EOY0 to EOY10 Existing void 6.9 2.0 3.2 12.0 Reward Pit 17.2 16.2 33.4 Process Water Dam 39.2 4.5 43.6 SD1 15.3 15.3 SD2 9.4 18.1 27.5 From EOY4 to EOY10 Bellbird South Pit 10.6 7.4 18.0 Bellbird North Pit 1.2 1.6 2.8 SD3 3.4 17.4 20.8

B5.2 WMS SCHEMATIC AND OPERATING RULES A schematised plan for the WMS configuration is shown in Figure B.4. Operating rules are provided in Table B.5. Further details of the proposed WMS is provided in Section 6 (in the main body of this report).



Figure B.2 – Catchments and landuses at the Reward Pit, from EOY0 to EOY10

Existing Green Parrot Pit



Figure B.3 – Catchments and landuses at the Bellbird Pit, from EOY4 to EOY10



Figure B.4 – Water management system schematic



Table B.5 – Water management system operating rules

Item Node Name Operating Rules

1 Raw Water System

1.1 Jervois Dam • Raw water supply for all site demands 1.2 Bore fields • Raw water supply for all site demands

2 Water Demands

2.1 Process Plant

• Continuous minimum raw water gross demand of 55 T/h (1.3 ML/d) supplied in priority order from the following sources:

o Underground Dewatering Dam

o Raw water system

• Additional net demand of 31.1 T/h (0.75 ML/d) supplied in priority order from the following sources:

o Process Water Dam

o Raw water system

2.2 Dust Suppression

• Demand rate varies over the Project life as shown in Table B.7

• Supplied in priority order from the following sources:

o Process Water Dam

o Raw water System

2.3 Underground mining

• Demand rate varies up to 0.1 ML/d when all three underground mines are operating (i.e. 0.03 ML/d for each underground mine

• Supplied in priority order from the following sources:

o Process Water Dam

o Underground Dewatering Dam

o Raw Water System

2.4 Potable water • Supplied from the raw water system at a rate of 0.1 ML/d.

3 Open-Cut Pits / Underground Mine

3.1 Reward Open Cut Pit

• Receives groundwater seepage at a maximum rate of 0.2 ML/d, but this will to be lost through pit evaporation on the pit surfaces, hence the net inflow is zero.

• Receives runoff from disturbed and undisturbed areas

• Continuous dewatering to the process water tank at a nominal rate of 0.5 ML/d

3.2 Bellbird (North and South) Open Cut Pits

• Receives groundwater seepage at a maximum rate of 0.05 ML/d, but this will to be lost through pit evaporation on the pit surfaces, hence the net inflow is zero.

• Receives runoff from disturbed and undisturbed areas

• Continuous dewatering to the process water tank at a nominal rate of 0.5 ML/d




3.3 Reward Underground Mine

• Receives groundwater inflows at the rates shown in Table B.9

• Continuous dewatering to the Underground Dewatering Dam

3.4 Bellbird Underground Mine



3.5 Rockface Underground Mine



4 Water Storages

4.1 Jervois Dam

• Receives runoff from undisturbed areas

• Supplies raw water to the following site demands:

o Process Plant

o Underground mining

o Potable water

o Dust suppression

• Overflows to Unca Creek when rainfall exceeds storage capacity

4.2 Process Water Dam

• Receives runoff from the Process Plant area

• Receives pumped water from the following sources:

o Raw water system

o Open cut pits

o Sediment dams

• Receives pumped return water from the following sources:

o Process Plant at a rate of 257.3 T/h (6.2 ML/d); and

o Tailings Storage Facility (TSF) at a rate of 33.8 T/h (0.8 ML/d)

• Supplies the following site demands:

o Process Plant

o Dust suppression


• The dam was set with a maximum operating storage level of 94.5 ML and a minimum operating storage level of 9.5 ML. Water is pumped from the raw water system to the Process Water Dam to maintain its minimum operating storage level. The supply from the raw water system to the process plant is limited to 0.85 ML/day, which is sufficient to supply the process water demand to the plant, and the underground mining equipment demand.




4.3 Underground Dewatering Dam

• Receives pumped groundwater inflows form the underground mines.

• Supplies raw water to the following site demands:

o Process Plant

o Dust suppression


• Overflows to the Process Water Dam when groundwater dewatering rate exceeds demands

4.5 Sediment Dams 1 and 2 (SD1 and SD2)

• Receive runoff from the Reward waste rock dump

• Pumped (dewatered) to Process Water Dam at a nominal rate of 0.5 ML/d from EOY0 to EOY4. Dewatering stops after EOY4.

• Overflows to Unca Creek when rainfall exceeds storage capacity

4.6 Sediment Dam 3 (SD3)

• Receive runoff from the Bellbird waste rock dump

• Pumped (dewatered) to Process Water Dam at a nominal rate of 0.5 ML/d from EOY0 to EOY4. Dewatering stops after EOY4.

• Overflows to a tributary of Unca Creek when rainfall exceeds storage capacity

B6 Catchment yield (AWBM) parameters The OPSIM model uses the Australian Water Balance Model (AWBM) (Boughton, 2010) to estimate runoff from rainfall. The AWBM model is illustrated in Figure B.5.

The AWBM is a saturated overland flow model which allows for variable source areas of surface runoff. The AWBM uses a group of connected conceptual storages (three surface water storages and one ground water storage) to represent a catchment. Water in the conceptual storages is replenished by rainfall and is reduced by evaporation. Simulated surface runoff occurs when the storages fill and overflow.

The model uses daily rainfalls and estimates of catchment evapotranspiration to calculate daily values of runoff using a daily water balance of soil moisture. The model has a baseflow component which simulates the recharge and discharge of a shallow subsurface store. Runoff depth calculated by the AWBM model is converted into runoff volume by multiplying the contributing catchment area.

The model parameters define the storage depths (C1, C2 and C3), the proportion of the catchment draining to each of the storages (A1, A2 and A3), and the rate of flux between them (Kb, Ks and BFI). Catchments across the site have been characterised into the following land use types:

• Natural/undisturbed;

• Hardstand;

• Mining pit; and

• Waste rock dump.



Figure B.5 – AWBM model (Boughton, 2010)

Table B.6 shows proposed AWBM parameters for this assessment. The proposed AWBM parameters were selected based on the following methodology:

• The natural/undisturbed catchment upstream of Jervois Dam is characterised as steep and rocky. For these areas, the proposed AWBM parameters were derived by calibrating the OPSIM model against recorded water levels and volumes in Jervois Dam. The calibration methodology and results are described in Section B7. The adopted AWBM parameters for “natural (steep and rocky)” catchment produces a long term volumetric runoff coefficient of 10%.

• The natural/undisturbed catchment downstream of Jervois Dam is characterised as flat and sandy, and is distinctly different to the catchment upstream of the dam. The calibrated AWBM parameters for “natural (steep and rocky)” catchment is likely to overestimate runoff yield in these areas. Therefore, for the flat and sandy natural/undisturbed catchment downstream of Jervois Dam, the proposed AWBM parameters were determined by adjusting the “natural (steep and rocky)” catchment AWBM parameters to produce a long term volumetric runoff coefficient of 5%, which is consistent with observations from past experience and previous studies.

• For other catchment types (mining pit, hardstand, and waste rock dump), the proposed AWBM parameters were determined by adjusting the natural catchment AWBM parameters until the long term volumetric runoff coefficient produced for each catchment type (compared to natural catchment) is consistent with observations from past experience and previous studies.



Table B.6 – Adopted AWBM parameters for various catchment types

AWBM parameter

Natural (steep and

rocky) a

Natural (flat and sandy) b

Mining pit Hardstand Waste rock

dump

A1 0.134 0.134 0.134 0.134 0.134

A2 0.433 0.433 0.433 0.433 0.433

A3 0.433 0.433 0.433 0.433 0.433

C1 15.0 25.0 3.5 3.5 10.5

C2 80.0 150.0 18.5 18.5 56.0

C3 70.0 130.0 16.0 16.0 49.0

BFI 0 0 0 0 0

Kb 0 0 0 0 0

Ks 0 0 0 0 0

Long-term volumetric

runoff coefficient

10% 5% 30% 30% 15%

a – Adopted for natural/undisturbed areas upstream of the Jervois Dam b – Adopted for natural/undisturbed areas downstream of the Jervois Dam

B7 OPSIM model calibration B7.1 METHODOLOGY The OPSIM model was calibrated to recorded water levels and volumes in Jervois Dam from 1977 to 2010 (the calibration period). The calibration was undertaken to ensure that the adopted AWBM parameters for natural catchment are suitable.

The adopted rainfall data over the calibration period is a combination DSITIA’s Patch Point data and recorded daily rainfall data at Jervois Dam as described in Section B3. Morton’s Lake evaporation (also obtained from DSITIA’s Patch Point data service) has been used to estimate evaporation loss from Jervois Dam.

It is also assumed that seepage (outflow) from Jervois Dam occurs at a constant rate of 200 kL/d. The adopted seepage rate of 200 kL/d was selected to achieve the best match between recorded and simulated dam volumes over the period of record.

B7.2 CALIBRATION RESULTS Figure B.6 compares recorded and simulated volumes in Jervois Dam over the calibration period. The model results show that the OPSIM model predicts most of the recorded peak volumes relatively well. The OPSIM model also predicted the rate of volume change in the dam relatively well. However, the OPSIM model was not able to replicate some of the recorded peak volumes, which is likely due to the poor representation of rainfall depths during these periods. Overall, the OPSIM model is expected to produce reasonable estimates of runoff yield from natural catchments using the adopted AWBM parameters.



Figure B.6 – Comparison of recorded and simulated volumes in Jervois Dam from 1977 to 2010

B8 Water demands B8.1 PROCESSING PLANT Based on the water mass balance process flow diagram provided by Sedgman, the Process Plant is projected to require a constant water demand rate of 86.1 T/h (2.05 ML/d) over the life of the Project, which includes a minimum demand rate of 55 T/h (1.3 ML/d) from the raw water system, and the remaining net demand rate of 31 T/h (0.75 ML/d) from other sources. The adopted Processing Plant water demand rate has accounted for all internal recycling of processed water.

B8.2 DUST SUPPRESSION Dust suppression demand rates were calculated based on the predicted surface area (waste rock dump, open cut pits, haul roads and access roads) to be wetted, and the average daily evaporation rate for during dry days. The following methodology was adopted:

• For mining pit and waste rock dumps, dust suppression demand was calculated assuming that 50% of the total area require dust suppression. Dust suppression is not required when the open cut pit or waste rock dump is no longer in operation.

• For haul roads and access roads, dust suppression demand was calculated based on a total road length of 13.9 km and road width of 30 m as per the proposed haul road layout supplied by KGL. The total road surface area requiring dust suppression will remain the same over the life of the Project.

• Based on the 129-year Patch Point data, there is an average of 354 dry days per year, and an average daily evaporation rate of 5.6 mm during these dry days. The daily dust suppression rate for each mine stage was calculated by multiplying the average daily evaporation rate (5.6 mm) and the surface area requiring dust suppression.

849.53

1280.66

0

200

400

600

800

1000

1200

1400

2/10/1977 25/03/1983 14/09/1988 7/03/1994 28/08/1999 17/02/2005

Volu

me

(ML)

Volume in Dam

Gauge Data

OPSIM Results



Table B.7 shows the adopted dust suppression demand rates over the Project life. It was assumed that the dust suppression water demand may be obtained from sources of lower water quality (via the Process Water Tank), such as harvested surface runoff and groundwater collected in-pit.

Table B.7 – Dust suppression demand

Project year

Area requiring dust suppression (ha) Total dust suppression

demand (kL/d) Mining Pit Waste rock dump

Haul roads / access roads

EOY0 to EOY4 16.2 33.4 41.6 3,605 EOY4 to EOY5 25.3 50.8 41.6 4,324 EOY5 to EOY6 25.3 44.1 41.6 4,142 EOY6 to EOY7 25.3 37.4 41.6 3,961 EOY7 to EOY8 25.3 30.8 41.6 3,779 EOY8 to EOY10 25.3 15.4 41.6 3,361

B8.3 POTABLE WATER DEMAND Based on the water mass balance process flow diagram provided by Sedgman, the predicted water demand rate to the Potable Water Treatment Plant is 3.8 T/h (0.1 ML/d). Based on an a plant yield of 50%, 1.9 T/h (0.05 ML/d) of treated water from the Potable Water Treatment Plant will be used to supply potable water uses at the mine camp and the administration area, while the remaining 1.9 T/h (0.05 ML/d) will be pumped to the process plant supply non-potable uses.

B8.4 UNDERGROUND MINE DEMAND A maximum nominal underground mining demand rate of 100 kL/d was adopted when all three underground mines (Rockface, Bellbird and Reward) are operating. That is, the adopted underground mine demand is 33.3 kL/d for each operating underground mine. Table B.8 shows the adopted underground mine demand rates over the Project life.

Table B.8 – Underground mining demand

Project year

Marshall / Reward

operations

Bellbird operations

Rockface operations


(kL/d)


(ML/yr)

EOY0 to EOY4 open cut only none underground only 33.3 12.2

EOY4 to EOY5 open cut + underground

open cut only



open cut only



open cut + underground



open cut + underground none 66.7 24.3


underground only none 66.7 24.3



B9 Water sources B9.1 JERVOIS DAM The Jervois Project will source raw water from Jervois Dam via a pipeline. Jervois Dam supplies site raw water demands in conjunction with the groundwater bore fields.

B9.2 GROUNDWATER BORE FIELDS The Project will also source raw water from groundwater bore fields. The groundwater bore fields supply site raw water demands in conjunction with Jervois Dam.

B9.3 GROUNDWATER INFLOWS TO OPEN CUT PITS AND UNDERGROUND MINES

Estimates of groundwater inflows to the open cut pits and the underground mines were provided by CloudGMS (2018). The estimates were provided separately for each underground mine and open cut pit in a sub-daily time step. The estimates were converted to a daily average inflow rate over each Project year. Table B.9 shows the adopted groundwater inflow rates over the life of the Project. Groundwater inflows are predicted to increase gradually to a maximum rate of 6,423 kL/d in Year 7, and then reducing to 4,765 kL/d at the end of the mine life.

Table B.9 – Predicted groundwater inflows underground mines

Project year

Adopted groundwater inflow rate (kL/d)

Underground Mine Total

Rockface Reward Bellbird

EOY0 0 0 0 0

EOY1 333 0 0 333

EOY2 1,147 0 0 1,147

EOY3 2,549 0 0 2,549

EOY4 3,247 0 0 3,247

EOY5 2,252 1,508 0 3,760

EOY6 1,943 4,004 0 5,948

EOY7 1,809 4,266 347 6,423

EOY8 1,671 2,985 1,605 6,262

EOY9 1,576 2,551 1,038 5,165

EOY10 1,505 2,341 920 4,765

B9.4 SURFACE RUNOFF Surface runoff from both disturbed and undisturbed areas will be captured in the proposed open cut pits and sediment dams, and then pumped to the Process Water Dam for re-use. The estimation of runoff yield is described in Section B6.



B10 Water storage sizing B10.1 PROCESS WATER DAM Figure B.2 shows the location, extent and catchment of the proposed Process Water Dam (PWD). The PWD was sized to fully utilise the area available to construct the dam, hence providing the maximum possible storage volume. The PWD will be formed by constructing an embankment across the existing Unca Creek channel just upstream of the proposed Reward Pit. The existing ground inside of the dam embankment will also be excavated at a slope of 1V:6H to provide additional volume. The proposed flood protection bund (described in Section 8.4) will form part of the northern dam embankment. The PWD will be constructed with an emergency spillway, which will direct excess flows to the proposed Unca Creek Diversion. Table B.10 shows key details of the proposed PWD.

Table B.10 – Process Water Dam (PWD) key details

Dam attribute Value

Invert level (mAHD) 345.3

Spillway invert level (mAHD) 348.5

Embankment crest level (mAHD) 349.0

Volume below spillway (ML) 183

Dam floor area 4.7

Surface area at full storage level (ha) 6.7

Batter slope (V:H) 1:6

B10.2 SEDIMENT DAMS The sediment dam volumes were sized to capture all runoff during a 10 year 24-hour rainfall event (a rainfall depth of 98.4 mm), assuming a runoff coefficient of 0.5. It should be noted that adopted sediment dam sizes exceed those recommended in IECA (2008).

Table B.11– Sediment dam sizing

Storage Cv Catchment Area (ha) Volume (ML)

SD1 0.5 15.3 7.5

SD2 0.5 27.5 13.5

SD3 0.5 20.8 10.2



– Hydrological and hydraulic model development

Contents

C1 Introduction ________________________________________________ 146 C2 Hydrological modelling ________________________________________ 146

C2.1 Methodology __________________________________________________ 146 C2.2 URBS model configuration _______________________________________ 146 C2.3 Estimation of Design discharges __________________________________ 150

C3 Hydraulic modelling __________________________________________ 153 C3.1 Methodology __________________________________________________ 153 C3.2 Existing conditions model Configuration ___________________________ 154 C3.3 Operational conditions model configuration ________________________ 154 C3.4 Final landform model configuration _______________________________ 155 C3.5 Jervois Dam spillway model configuration __________________________ 155 C3.6 Model results __________________________________________________ 155



C1 Introduction This appendix outlines the development of the hydrological and hydraulic models of the Unca Creek catchment. These models have been used to estimate design discharges, flood levels, flood extents and velocities under existing conditions, operational conditions and the final landform. The model results were used to assess the flood impacts of the Project during key stages of the Project life.

C2 Hydrological modelling C2.1 METHODOLOGY The Unified River Basin Simulator (URBS) runoff-routing model (Carroll, 2016) was used to estimate flood discharges in the Roper Creek catchment. URBS is a runoff-routing computer model that uses a network of conceptual storages to represent the routing of rainfall excess through a catchment. URBS is used extensively throughout Australia by the Bureau of Meteorology (BoM) for flood forecasting on major river systems.

For this study, the URBS model was used in “split mode”, which enables the simulation of separate catchment and channel routing. Adopted rainfall losses are subtracted from the total rainfall hyetograph to obtain rainfall excess. Rainfall excess is routed through a conceptual storage representing each sub-catchment of the model before being added to the creek or river channel. Routing through the creek or river system uses the Muskingum method.

For this assessment, URBS models was developed for existing and operational conditions. The only difference between the two models is the configuration of the Jervois Dam spillway. The existing conditions URBS model incorporates the existing Jervois Dam spillway configuration. The operational conditions URBS model incorporates the raised and widened spillway configuration proposed for the operational phase of the Project.

There is no suitable data to calibrate the URBS model. Therefore, the URBS model catchment and routing parameters were obtained from the Todd River URBS model previously developed by WRM as part of the Alice Springs Flood Investigation and Mapping Study (WRM, 2015). The design rainfall losses were obtained from the AR&R data hub in accordance with the AR&R 2016 guidelines (Ball et al, 2016).

The WRM (2015) URBS model was calibrated to three historical events and verified against 11 other events. Given the similarities between the Todd River and Unca Creek catchment characteristics, the model parameters obtained from the WRM (2015) study are considered robust and suitable for use in the flood assessment for the Project.

C2.2 URBS MODEL CONFIGURATION

Model extent and subcatchment areas

Figure C.1 shows the configuration of the Unca Creek URBS model. The model extends to the Jervois Range approximately 5 km upstream (west) of the Project and 6 km downstream (east) of the Project. The model consists of 56 subcatchments ranging in size from 0.2 km2 to 2.8 km2. Table C.1 shows the adopted subcatchment areas.

URBS model parameters

Table C.2 shows the adopted URBS global parameters (α, β and m). Initial and continuing rainfall losses were determined based on the AR&R 2016 guidelines (Ball et al, 2016) and are discussed in Section A2.3.4.



Figure C.1 – URBS model configuration



Table C.1 – Adopted URBS model subcatchment areas

Subcatchment ID

Area (km2)

Subcatchment ID

Area (km2)

Subcatchment ID

Area (km2)

1 1.99 22 0.98 43 0.92

2 0.52 23 1.16 44 0.39

3 2.68 24 0.90 45 1.32

4 1.41 25 0.99 46 0.81

5 0.49 26 0.89 47 1.26

6 0.44 27 0.87 48 1.18

7 0.41 28 0.56 49 1.69

8 0.31 29 1.43 50 1.36

9 0.42 30 0.85 51 0.97

10 0.55 31 0.94 52 0.89

11 0.22 32 0.34 53 1.84

12 0.52 33 0.19 54 1.53

13 1.08 34 0.58 55 2.08

14 1.86 35 0.76 56 2.32

15 1.26 36 0.32 57 0.69

16 0.85 37 0.61 58 2.21

17 1.42 38 0.66 59 1.28

18 0.35 39 1.94 60 0.88

19 0.33 40 2.82 61 1.01

20 0.57 41 2.15 - -

21 2.04 42 1.13 - -

Table C.2 – Adopted URBS model catchment and routing parameters

Parameter Value

α (channel lag parameter) 0.20

β (catchment lag parameter) 5.00

m (catchment non-linearity parameter) 0.55

Jervois Dam

Jervois Dam was incorporated within Subcatchment 19 in the URBS model. Jervois Dam was modelled in URBS using a spillway stage-discharge relationship. Using this approach, a given volume of water stored upstream of the dam corresponds to an outflow discharge from the spillway. This approach also assumes that the dam is full at the start of each simulation.

Table C.3 shows the adopted spillway configuration under existing conditions and operational conditions. Figure C.2 compares the adopted stage-discharge relationships for existing and operational conditions. The adopted stage-discharge relationships for Jervois Dam (shown in Figure C.2) were derived using the following methodology:



• For existing conditions, the stage-discharge relationship for the existing spillway was derived using a TUFLOW hydraulic model developed for the existing spillway channel (described in Section A3.5).

• For operational conditions, the stage-discharge relationship was derived using the broad-crested weir equation.

Note that the spillway is significantly wider under operational conditions. Therefore, the upgraded spillway would operate more efficiently compared to the existing spillway, resulting in a higher outflow discharge for a given depth of water above the spillway.

Table C.3 – Adopted Jervois Dam spillway characteristics

Figure C.2 – Adopted stage-discharge relationships for the Jervois Dam spillway under existing and operational conditions

366

367

368

369

370

371

372

373

374

375

376

0 200 400 600 800 1000 1200 1400 1600 1800

Dam

sta

ge (

mAH

D)

Spillway outflow discharge (m3/s)

Existing spillway(existingconditions)

Raised spillway(operationalconditions)

Existing spillwayinvert level

Raised spillwayinvert level

Dam wall crest

Parameter Existing conditions

Operational conditions

Spillway invert level (mAHD) 367.38 370.00

Spillway width (m) 4.00 30.00

Dam crest level (mAHD) 372.25 372.25



C2.3 ESTIMATION OF DESIGN DISCHARGES

Overview

The URBS model was used to estimate design flood discharges in Unca Creek and its tributaries in the vicinity of the Project for the 10%, 1%, 0.1% AEP and probable maximum precipitation (PMP) events. The following guidelines were adopted for this assessment:

• For the 10% and 1% AEP events, design discharges were estimated using the AR&R 2016 (Ball et al, 2016) guideline.

• For the 0.1% AEP and PMF events, the following guidelines were adopted:

o The Estimation of Probable Maximum Precipitation in Australia: Generalised Short Duration Method - GSDM (BoM, 2003);

o Guidebook to the Estimation of Probable Maximum Precipitation: Generalised Tropical Storm Method – Revised Edition - GTSMR (BoM, 2005); and

o Growth curves and temporal patterns of short duration design storms for extreme events (Jordan, 2005).

Design rainfalls

Table C.4 shows the adopted design rainfalls depths for a range of events from 10% AEP to the PMF and for a range of storm durations between 0.5 and 72 hours. The following is of note with regards to the adopted design rainfalls:

• For the 10% and 1% AEP events, design rainfalls were obtained from the Bureau of Meteorology (BoM);

• For the 0.1% AEP event, design rainfalls for durations of 24 hours or longer were obtained from BoM. No extreme event design rainfall estimates are currently available from BoM for durations shorter than 24 hours. Therefore, 0.1% AEP design rainfalls for durations shorter than 24 hours were derived by applying the Jordan (2005) growth curves to the 1% AEP design rainfalls.

• For the PMP event, design rainfalls for durations up to and including 3 hours were estimated using the GSDM (BoM, 2003) method. The GTSMR (BoM, 2005) method was adopted for durations equal to or longer than 24 hours. PMP design rainfalls for durations between 3 and 24 hours were interpolated between the GSDM and GTSMR estimates.

• Aerial reduction factors (ARFs) were applied to the design rainfalls in accordance with the AR&R 2016 guideline. ARFs were calculated based on the catchment area to key locations within the Project. Using this approach, the adopted ARF would vary depending on the location where discharges are extracted from the model.

Temporal patterns

For the 10% and 1% AEP events, the ‘ensemble’ temporal pattern approach described in AR&R 2016 (Ball et al, 2016) was adopted. The AR&R 2016 temporal pattern methodology involves the use of an ‘ensemble’ of 10 temporal patterns, which produces 10 design storms for each duration for each AEP. The temporal pattern which results in a peak flood discharge closest to the average of the 10 design storms for each storm duration was selected as the representative temporal pattern for that storm duration.

For the 0.1% AEP and PMP events, the 10 historical temporal patterns provided in Jordan (2005) were applied to the design rainfalls for durations up to and including 6 hours, while the 10 historical temporal patterns from the GTSMR (BOM, 2005) method were applied for durations longer than 6 hours. Similar to the AR&R 2016 ensemble approach, the temporal pattern which results in a peak flood discharge closest to the average of the 10 design storms for each storm duration was selected as the representative temporal pattern for that storm duration.



Table C.4 – Adopted design rainfall depths

Duration (hours)

Design rainfall depth (mm)

10% AEP 1% AEP 0.1% AEP PMP 0.5 32.1 54.5 82.5 220.0

0.75 37.2 63.7 96.3 280.0

1 40.7 69.9 105.8 330.0

1.5 45.8 78.6 118.9 380.0

2 49.2 84.6 128.0 430.0

3 54.3 93.3 141.2 490.0

5 59.9 102.6 155.2 557.5

6 64.8 109.8 166.1 611.0

9 72.3 122.4 185.2 695.2

12 78.6 133.2 201.5 761.9

18 89.5 152.1 230.1 866.9

24 98.4 168.5 266.4 950.0

30 106.5 183.3 288.4 1065.4

36 113.4 196.6 307.7 1170.0

48 124.8 219.8 340.8 1360.0

72 141.8 254.9 398.9 1720.0

Design rainfall losses

Design initial (IL) and continuing (CL) losses were derived based on the average of ILs and CLs adopted for the 14 calibration events in the Todd River URBS model (WRM, 2015). For the 10% and 1% AEP events, an IL of 35 mm and a CL of 3.5 mm/h were adopted. For the 0.1% AEP and PMP events, an IL of zero and a CL of 3.0 mm/h were adopted.

Design discharges

Table C.5 shows the URBS model peak discharges in Unca Creek just upstream of the Project (URBS Subcatchment 43) under existing and operational conditions. Table C.5 also show the critical storm duration and representative temporal pattern. For the purpose of this assessment, it was assumed that the dam upgrade works will not change the critical storm duration and representative temporal pattern.

Figure C.3 and Figure C.4 show the distribution of peak discharges in Unca Creek just upstream of the Project (URBS Subcatchment 43), estimated from the ensemble of 10 temporal patterns for each storm duration for the 10% and 1% AEP events respectively under existing conditions.

The distribution of peak discharges shown in Figure C.3 and Figure C.4 is represented as a box and whisker plot for each duration. For each duration, the rectangle box represents the 25%ile and 75%ile (1st and 3rd quartile, the interquartile range or IQR) bound of the estimate. The black horizontal line (whiskers) represents the upper and lower estimates for 1.5 times of the IQR. The red horizontal line within the box is the median value and the red dot represents the mean value.

The results indicate that proposed spillway upgrade will increase peak discharges in Unca Creek by between 11% and 21%. This is due to the significantly wider spillway under operational conditions, allowing more water to flow over the spillway for a given depth above the spillway invert.



Table C.5 – Predicted design peak discharges and critical storm durations in Unca Creek upstream of the Project (URBS Subcatchment 43)

Event Peak discharge (m3/s)

Critical duration (hours)

Representative temporal pattern #

Existing conditions

10% AEP 7.8 48 8

1% AEP 28.8 12 5

0.1% AEP 66.6 6 8

PMP 797.6 2 2

Operational conditions (raised dam spillway)

10% AEP 10.2 48 8

1% AEP 34.1 12 5

0.1% AEP 89.5 6 8

PMP 880.9 2 2

Figure C.3 – Distribution of 10% AEP design peak discharges in Unca Creek upstream of the Project (URBS subcatchment 43), existing conditions



Figure C.4 – Distribution of 1% AEP design peak discharges in Unca Creek upstream of the Project (URBS subcatchment 43), existing conditions

C3 Hydraulic modelling C3.1 METHODOLOGY The TUFLOW hydrodynamic model (WBM, 2016) was used to simulate the flow behaviour of Unca Creek and its tributaries in the vicinity of the Project. TUFLOW represents hydraulic conditions on a fixed grid by solving the full two-dimensional depth averaged momentum and continuity equations for free surface flow. The model automatically identifies breakout points and flow directions within the study area. There is no available data to calibrate the TUFLOW model. All hydraulic modelling was undertaken using the TUFLOW Build 2017-09-AC HPC-GPU solver.

Hydraulic modelling was undertaken for the following scenarios:

• The 10% and 1% AEP events under existing and operational conditions. This scenario was undertaken to assess the impact of the Project on peak flood levels, extents and velocities for the 10% and 1% AEP events.

• The 0.1% AEP event under operational conditions. This scenario was undertaken to assess the hydraulic performance of the proposed Unca Creek Diversion and assess the flood immunity of the Reward Pit during operational conditions.

• The PMF event under final landform conditions. This scenario was undertaken to estimate peak flood levels, depths and extents for the proposed final landform site configuration.

A smaller hydraulic model of the Jervois Dam spillway was also developed to derive a stage-discharge relationship for the existing dam spillway. The stage-discharge relationship



of the Jervois Dam spillway derived using this model was incorporated into the URBS hydrologic model (described in Section A2.3).

C3.2 EXISTING CONDITIONS MODEL CONFIGURATION

Overview

Figure C.5 shows the extent of the existing conditions TUFLOW model of the Unca Creek catchment. The model covers an area of 44.9 km2 and extends east to Jervois Dam (2 km upstream of the Reward Pit) and west approximately 5.5 km downstream of the Reward Pit. The model includes Unca Creek, the Southern Unca Creek Tributary and an unnamed gully to the north of Unca Creek. The model was configured with a grid cell size of five metres.

Topography

Nitro Solutions provided LiDAR topographic survey for the Project area in February 2018. The data (flown in early 2018) was supplied as ground strike elevation points at four metre spacing. The data was converted to a digital elevation model (DEM) for use in the hydraulic model.

Inflow and outflow boundaries

Figure C.5 shows the locations of inflow and outflow boundaries in the TUFLOW model. The model includes a total of 3 ‘total’ and 40 ‘local’ inflow boundaries as well as two outflow boundaries.

The 40 local inflow boundaries were applied within the 2D model domain using 2D surface-area “SA” polygons. The three total inflow boundaries at the upstream end of the model were configured using 2D flow-time “QT” boundaries. Existing conditions discharge hydrographs extracted from the URBS hydrologic model were applied to these TUFLOW inflow boundaries.

The model includes one outflow boundary in Unca Creek and one in the unnamed gully (north of Unca Creek). Outflow boundaries for these two locations were configured using a ‘normal-depth’ approach based on a slope of 0.4% in Unca Creek and 1% in the unnamed gully, which are equal to the creek bed slope at these locations.

Hydraulic roughness

Hydraulic roughness in the TUFLOW model is represented by the Manning’s ‘n’ roughness coefficient. For this assessment, a uniform Manning’s ‘n’ of 0.04 was applied to the entire Project area. This is considered appropriate given the sparse vegetation over the entire Project area, and similar surface characteristics between the creek channels and overbank areas.

C3.3 OPERATIONAL CONDITIONS MODEL CONFIGURATION The existing conditions TUFLOW model was modified to incorporate the raised Jervois Dam spillway and the proposed Unca Creek diversion during the operational phase of the Project. Figure C.6 shows the operational conditions TUFLOW model configuration.

The following changes were made to the existing conditions TUFLOW model:

• The proposed Unca Creek diversion was incorporated into the 2D model topography, while the proposed flood protection bunds were modelled as glass walls (completely impervious to flood flows);

• To reflect the operational conditions drainage characteristics, local inflow boundaries “Jer046” and “Jer047” were relocated to the base of proposed diversion channel; and

• Discharge hydrographs from the operational conditions URBS model were applied to the inflow boundaries in the model. The updated discharge hydrographs reflect the changes in outflow peak discharges due to the upgraded dam spillway.



C3.4 FINAL LANDFORM MODEL CONFIGURATION The operational conditions TUFLOW model was modified slightly to reflect the final landform site configuration. Figure C.7 shows the TUFLOW model configuration for the final landform. Compared to the operational conditions model, the proposed flood protection bunds were extended, and the Reward waste rock dump extent was modelled as a full blockage to flood flows.

C3.5 JERVOIS DAM SPILLWAY MODEL CONFIGURATION Figure C.8 shows the TUFLOW configuration for the existing Jervois Dam Spillway. The model covers an area of 0.84 ha and extends between just upstream of the embankment to the bottom of the spillway channel. The model was configured with a grid cell size of one metre. The model topography was configured using detailed ground survey data of the spillway channel supplied by Nitro Solutions and undertaken in February 2018. A Manning’s ‘n’ hydraulic roughness coefficient of 0.04 was adopted for the entire model.

The model has a single “SA” inflow boundary located just upstream of the spillway crest. A single normal depth outflow boundary was adopted at the bottom of the spillway channel based on a slope of 6%. An initial dam water level of 367.35 mAHD was adopted. The model was run for nominal flows of up to 500 m3/s.

C3.6 MODEL RESULTS

Existing conditions flooding

Figure 8.1 and Figure 8.2 (in the main body of this report) show the peak flood levels, depths and extents across the entire Project area for the 10% AEP and 1% AEP events under existing (pre-mine) conditions. Figure 8.4 and Figure 8.5 (in the main body of this report) show the corresponding peak flood velocities for the 10% and 1% AEP events. Figure 8.3 and Figure 8.6 (in the main body of this report) show the existing conditions peak flood depths and velocities respectively in the vicinity of the Reward Pit and Process Plant area.

Operational conditions flooding

Figure 8.7 and Figure 8.8 (in the main body of this report) show the peak flood levels, depths and extents across the entire Project area for the 10% AEP and 1% AEP events under operational conditions. Figure 8.10 and Figure 8.11 (in the main body of this report) show the corresponding peak flood velocities for the 10% and 1% AEP events. Figure 8.9 and Figure 8.13 (in the main body of this report) show the operational conditions peak flood depths and velocities respectively in the vicinity of the Reward Pit and Process Plant area.

Unca Creek Diversion flood assessment

The operational conditions TUFLOW model was used to assess the hydraulic behaviour of the proposed Unca Creek Diversion, and to assess the flood immunity of the Reward Pit. The results are described in Section 8.4.3 of this report.

Final landform flooding

Figure 8.22 (in the main body of this report) shows the extent of the PMF from Unca Creek for the final landform at the Marshall-Reward operational area.

Existing Jervois Dam spillway stage-storage relationship

Figure C.2 in Section C2.2.3 shows the stage-discharge relationship for the existing spillway derived using the Jervois Dam Spillway TUFLOW model results.



Figure C.5 – Existing conditions TUFLOW model configuration



Figure C.6 – Operational conditions TUFLOW model configuration



Figure C.7 – Final landform TUFLOW model configuration



Figure C.8 – TUFLOW model configuration for the existing Jervois Dam spillway


appendices - ntepa.nt.gov.au

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