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CHAPTER 6 – WATER MANAGEMENT

GULF ALUMINA LTD – SKARDON RIVER BAUXITE PROJECT

Skardon River Bauxite Project Chapter 6 – Water Management

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TABLE OF CONTENTS

6.1 Introduction .......................................................................................................6-1 6.2 Legislative and Policy Context .............................................................................6-1 6.2.1 Water Supply (Safety and Reliability) Act 2008 .......................................................... 6-1 6.2.2 Manual for Assessing Consequence Categories and Hydraulic Performance

of Structures ............................................................................................................... 6-1 6.2.3 Structures which are Dams or Levees Constructed as Part of

Environmentally Relevant Activities........................................................................... 6-1 6.2.4 Groundwater Licence ................................................................................................. 6-1 6.3 Environmental Objectives and Performance Outcomes .......................................6-2 6.3.1 Environmental Objectives .......................................................................................... 6-2 6.3.2 Performance Outcomes ............................................................................................. 6-2 6.4 Water Management Strategy and Infrastructure .................................................6-3 6.4.1 Mine Plan Alignment .................................................................................................. 6-3 6.4.2 Mine Pits ..................................................................................................................... 6-3 6.4.2.1 Mine Site Sediment Management ............................................................................. 6-4 6.4.2.2 Mine Site Sediment Pond Management .................................................................... 6-5 6.4.3 Port Infrastructure Area ............................................................................................. 6-6 6.4.3.1 Overview .................................................................................................................... 6-6 6.4.3.2 Pond Sizing and Catchments ...................................................................................... 6-6 6.4.3.3 Sediment Type within Pond Catchments ................................................................... 6-7 6.4.3.4 Engineering Design Standards .................................................................................... 6-7 6.4.3.5 Sediment Management – Wet Season and Operational Period ................................ 6-8 6.4.3.6 Bauxite Stockpile Sediment Control ........................................................................... 6-9 6.4.3.7 Contaminant Management ........................................................................................ 6-9 6.4.3.8 Modelling of Pond Capacity ....................................................................................... 6-9 6.4.3.9 Release Management ............................................................................................... 6-11 6.4.3.10 Existing Sediment Pond Design ................................................................................ 6-11 6.4.3.11 Design Features ........................................................................................................ 6-11 6.4.3.12 Release Monitoring .................................................................................................. 6-12 6.4.3.13 Preliminary Regulated Dam Assessment ................................................................. 6-14 6.4.4 Erosion and Sediment Control ................................................................................. 6-15 6.4.4.1 Erosion and Sediment Control Plan ......................................................................... 6-16 6.4.4.2 Permanent Haul Roads ............................................................................................. 6-17 6.4.5 Namaleta Creek Crossing ......................................................................................... 6-18 6.4.5.1 Location .................................................................................................................... 6-18 6.4.5.2 Existing Crossing ....................................................................................................... 6-18 6.4.5.3 Crossing Design ........................................................................................................ 6-20 6.4.5.4 Crossing Drainage ..................................................................................................... 6-25 6.4.5.5 Crossing Construction and Rehabilitation ................................................................ 6-25 6.4.6 Crossings of other Drainage Features ...................................................................... 6-25 6.4.7 Operation of the Water Management System ........................................................ 6-30 6.4.7.1 Responsibility ........................................................................................................... 6-30 6.4.7.2 Emergencies ............................................................................................................. 6-30 6.4.7.3 Climatic Impacts ....................................................................................................... 6-30 6.4.7.4 Controls to Prevent Failure ...................................................................................... 6-31 6.4.7.5 Discharge Management ........................................................................................... 6-31 6.5 Water Balance .................................................................................................. 6-31 6.5.1 Water Demand ......................................................................................................... 6-31


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6.5.1.1 Potable Water .......................................................................................................... 6-31 6.5.1.2 Vehicle Washdown ................................................................................................... 6-31 6.5.1.3 Dust Suppression ...................................................................................................... 6-32 6.5.1.4 Product Moisture Content ....................................................................................... 6-32 6.5.1.5 Construction and Maintenance ................................................................................ 6-32 6.5.2 Demand Summary .................................................................................................... 6-32 6.5.3 Water Supply ............................................................................................................ 6-34 6.5.3.1 Water Supply Strategy ............................................................................................. 6-34 6.5.3.2 Kaolin Mine Water Storages .................................................................................... 6-35 6.5.3.3 Shallow Aquifers ....................................................................................................... 6-35 6.5.3.4 Sediment Ponds........................................................................................................ 6-38 6.5.3.5 Great Artesian Basin and New Dams ....................................................................... 6-38 6.5.4 Supply Summary ....................................................................................................... 6-38 6.5.5 Supply and Demand Forecasts ................................................................................. 6-39 6.5.6 Demand and Supply Management ........................................................................... 6-39

Tables

Table 6-1 Catchments Areas, Sediment Runoff and In-pit Pond/Dam Sizing ............................ 6-5 Table 6-2 Preliminary Consequence Category Assessment ..................................................... 6-14 Table 6-3 Demand Summary .................................................................................................... 6-34 Table 6-4 Existing Supply Sources ............................................................................................ 6-38

Figures

Figure 6-1 Port Area Sediment Ponds, Catchments and Drainage ............................................ 6-13 Figure 6-2 Namaleta Creek Crossing Location ........................................................................... 6-19 Figure 6-3 Namaleta Creek Crossing – Downstream View ........................................................ 6-24 Figure 6-4 Haul Road Crossing of Drainage Feature .................................................................. 6-29 Figure 6-5 Seasonal Water Application Rates for Dust Suppression ......................................... 6-32 Figure 6-6 Water Demand (High / Medium Quality) ................................................................. 6-33 Figure 6-7 Water Demand (Low Quality) .................................................................................. 6-33 Figure 6-8 Estimated Yield of Kaolin Water Storages ................................................................ 6-35 Figure 6-9 Existing and Proposed Bores for Water Supply ........................................................ 6-37 Figure 6-10 Water Balance Summary .......................................................................................... 6-39


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6. WATER MANAGEMENT

6.1 Introduction

This chapter describes the water management strategy for the Project to manage runoff from mining areas, the Port infrastructure area and other activity / infrastructure areas. Water management infrastructure is proposed and a regulated dam assessment has been undertaken for the proposed Port area sediment pond. Project water demand has been estimated and a water supply strategy based on existing water sources (kaolin mine water storages and shallow aquifer bores) and additional shallow aquifer bores has been proposed.

This chapter informs the management of impacts to surface water (Chapter 12) and groundwater (Chapter 13). Chapter 12 and Chapter 13 provide a description of all mitigation and management measures designed to achieve environmental objectives and performance outcomes for surface water and groundwater.

Gulf Alumina manages the decommissioned kaolin mine (in care and maintenance) under a Plan of Operations and Rehabilitation Plan, with the current plan covering the period from February 2015 to February 2016. In addition, the existing EA for the mining leases conditions environmental management of the kaolin mine whilst in care and maintenance, including rehabilitation and decommissioning, and management and monitoring of water. Water management, rehabilitation and decommissioning for the kaolin mine is described in Chapter 7 and the environmental management plan (EM Plan) provided in Appendix 13.

6.2 Legislative and Policy Context

6.2.1 Water Supply (Safety and Reliability) Act 2008

The Water Supply (Safety and Reliability) Act 2008 is described in Chapter 2.

6.2.2 Manual for Assessing Consequence Categories and Hydraulic Performance of Structures

The Manual for Assessing Consequence Categories and Hydraulic Performance of Structures (EHP, 2013) (the Manual) sets out the requirements of the administering authority, for consequence category assessment and certification of the design of ‘regulated structures’, constructed as part of environmentally relevant activities (ERAs) under the EP Act.

6.2.3 Structures which are Dams or Levees Constructed as Part of Environmentally Relevant Activities

EHP has produced the Guideline - Structures which are Dams or Levees Constructed as Part of Environmentally Relevant Activities (EHP, 2014) (the Guideline for Dams or Levees). The management measures described in this chapter adopt the relevant conditions described in the Guideline for Dams or Levees, where relevant to the proposed water management infrastructure.

6.2.4 Groundwater Licence

An existing subartesian water licence which was awarded to Gulf on the 24 July 2012, which allows for 55 ML per annum from shallow aquifer bores in the Project area. Additional approvals under the Water Act 2000 are likely to be required for water supply from shallow aquifers greater than 55 ML per annum.


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6.3 Environmental Objectives and Performance Outcomes

The environmental objectives and performance outcomes below are based on Schedule 5, Table 2 of the Environmental Protection Regulations 2008 (EP Regulation). The mitigation and management measures presented in this chapter are designed to achieve these environmental objectives and performance outcomes. The environmental management plan (EM Plan) presented in Appendix 13 provides a consolidated description of these mitigation and management measures.

6.3.1 Environmental Objectives

The activity will be operated in a way that protects environmental values of waters.

The activity will be operated in a way that protects the environmental values of wetlands.

The activity will be operated in a way that protects the environmental values of groundwater and

any associated surface ecological systems.

The choice of the site, at which the activity is to be carried out, minimises serious environmental

harm on areas of high conservation value and special significance and sensitive land uses at adjacent

places.

The design of the facility (water management infrastructure) permits the operation of the site at

which the activity is to be carried out is in accordance with best practice environmental

management.

6.3.2 Performance Outcomes

Contingency measures will prevent or minimise adverse effects on the environment due to

unplanned releases or discharges of contaminants to water.

The activity will be managed so that stormwater contaminated by the activity that may cause an

adverse effect on an environmental value will not leave the site without prior treatment.

Any discharge to water or a watercourse or wetland will be managed so that there will be no

adverse effects due to the altering of existing flow regimes for water or a watercourse or wetland.

The activity will be managed so that adverse effects on environmental values are prevented or

minimised.

The activity will be managed in a way that prevents or minimises adverse effects on wetlands.

The activity will be managed to prevent or minimise adverse effects on groundwater or any

associated surface ecological systems.

Areas of high conservation value and special significance likely to be affected by the proposal are

identified and evaluated and any adverse effects on the areas are minimised, including any edge

effects on the areas.

Critical design requirements will prevent emissions having an irreversible or widespread impact on

adjacent areas.

Regulated structures comply with the ‘Manual for Assessing Consequence Categories and Hydraulic

Performance of Structures’ (EHP, 2013).


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6.4 Water Management Strategy and Infrastructure

6.4.1 Mine Plan Alignment

Strategies developed for Project water management have been aligned with the mine plan presented in Chapter 5. The following aspects of the Project will affect water management:

Mining will occur over ten years.

Progressive rehabilitation (refer Chapter 7) including replacing excavated topsoil and subsoil in open

mining areas.

Mining will be undertaken in the dry season only and therefore it is assumed that operational water

demand during the months of wet season will be low to negligible.

No beneficiation of bauxite will be required and hence this is not a source of water demand.

The addition of water to bauxite stockpiles is only likely to be required in the drier months.

The bauxite stockpile will be well drained and allow for rapid turnover of stocks to avoid build ups of

wet, sticky ore.

It has been assumed that road trains will be used for bauxite haulage – this will result in a

conservative worst case scenario for impact assessment with significant dust uplift and dust

suppression is expected to be the highest operational water demand.

Average distances from mining areas to the bauxite stockpile at the Port are typically 12 km, and the

haul road will need to be 12 m wide to accommodate the necessary plant.

A haul road crossing over Namaleta Creek will be required for access to mine pits south of the

Creek.

There is no demand for water as part of the power supply to the mine.

Water management for mine site involves managing runoff from the following mine domains:

mine pits

Port infrastructure area

other infrastructure and activities (e.g. construction activities, haul roads, limited soil stockpiles).

Any further refinements to the water management plan presented in this chapter will be determined during detailed engineering and design for the Project prior to the commencement of Project operations.

6.4.2 Mine Pits

During operational periods, rainfall runoff entering the pit will be drained internally and contained within the pit, to be lost as evaporation and as recharge to local aquifers. Mine pits are shown in Chapter 5, Figure 5-14.

Due to the nature of bauxite mining (shallow pits to approximately 6 m depth, located at the top of localised catchments and hydrogeology of pit areas allowing seepage from pits) there is no requirement for external storage and release of water captured within pits.

Surface water runoff does not occur as long as the mine floor lies below the surrounding terrain. Stormwater drains through the groundwater system. This process is enhanced by deep ripping of the mine floor, which will occur prior to the wet season in most bauxite mining areas. Placement of soil and bauxite waste on the mine floor will be even and parallel to the mine floor topography, which will closely parallel to the original land surface. The edges of mining areas will be battered down to a 5:1


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slope and re-vegetated as for the mine floor. Erosion within mined areas is negligible due to the generally flat or gently sloping terrain.

To prevent surface water runoff from mining areas the following measures will be adopted for erosion and sediment management:

Clearing and mining will not be carried out in areas of steep drop-off slope from the general terrain

– expected generally to be within 100 m of natural waterways and swamps.

Ripping will be conducted along contour lines, or offset to direct water away from valleys, using

Keyline principles (i.e. management of the topography to control runoff).

Should a low area be (erroneously) mined on the edge of a mining area, with potential to allow out-

flow of stormwater, earth bunds and silt traps will be constructed, as well as strategic contour banks

on the mine floor to direct flow away from the area. All structures would be stabilized with

establishment of grass cover, trees and shrubs.

Resource surveys have been undertaken to inform the location of economic bauxite resources. This has resulted result in accurate delineation of pits areas which avoid:

buffer zones around wetland and watercourses (refer to Chapter 15)

low lying areas with the potential to require erosion and sediment control measures to prevent

outflow from pits

unnecessary clearance of vegetation in areas that will not be mined.

Land clearing in advance of mining will be undertaken in the dry season. Gulf Alumina will undertake annual vegetation clearing, windrowing and burning in advance of proposed mining. Mining will generally occur in the same year (i.e. during the dry season) and therefore there is limited potential for erosion following clearing activities. Following clearing and prior to mining, these areas will be stabilised by allowing regrowth of grasses and shrubs and to maintain viability of the soil for plant growth. Where there is a risk of increased sedimentation from areas cleared of deep rooted vegetation, erosion and sediment control measures (refer to Section 6.4.4) will be implemented.

6.4.2.1 Mine Site Sediment Management

The topography of the Project area is shown in Chapter 10 and is generally low lying and flat with topography rising towards a ridge where bauxite deposits are located. The Project mining leases are at around 5 – 20 mAHD elevation where bauxite deposits occur, 3 - 8 mAHD at the Port infrastructure area and lower in creek and wetland areas. The bauxite pits are located at the top of the local catchments and hence external catchments reporting to the pits will be minimal.

Under the proposed mining approach, there will be no sediment runoff from mining areas to surrounding land and waters as runoff will be managed within the pits. Sediment ponds receiving drainage from the disturbed mining areas will be located in pit. Design will be carried out in accordance with best practice approaches and as part of an Erosion and Sediment Control Plan (ESCP). The ESCP will be developed in line with the International Erosion Control Association (IECA) Manual (IECA, 2008)which provides guidelines for erosion control on site, sediment pond design and construction, and their operation and maintenance.

The design and management details for in pit sediment ponds will be determined as an ongoing operational activity. However, preliminary estimates have been made for the sediment runoff volumes, and indicative geometric requirements for the expected sediment ponds within each pit. As described in Appendix 4, pond sizing was completed using the CALM approach (Witheridge and Walker, 1996). The approach depends on the erodibility of soil, peak runoff discharge and the volume of sediment likely to


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enter the structure. The basin surface area is determined as a function of the inflow rate and the target particle settling velocity.

The estimate catchments areas for each pit, sediment runoff volume and in-pit pond sizes and are provided in Table 6-1. Nominal sediment basin volumes range between 400 m3 and 88100 m3 with minimum storage depth requirements of between 2.0 and 2.3 m. This depth requirement could be reduced further, subject to pond management practices, with regular scouring and dredging to maximise containment volumes. The nominal in-pit pond size is approximately 0.5% of the pit catchment area for each pit. It is clear that in-pit sediment ponds will occupy a minor portion of each pit and that the pit itself will act to capture any runoff should the sediment basins overtop.

Table 6-1 Catchments Areas, Sediment Runoff and In-pit Pond/Dam Sizing

Pit Local Catchment Area (ha)

Sediment Volume (m3/y)

Nominal Pond Area (m2)

Minimum Storage Depth (m)

Pond Volume (m3)

Pit 1 78.1 5639 3300 2.1 7055

Pit 2 31.0 2238 1400 2.0 2855

Pit 3 296.0 21337 25000 2.1 53436

Pit 4 7.4 536 350 2.0 693

Pit 5 27.8 2007 1200 2.1 2527

Pit 6 4.4 318 200 2.0 407

Pit 7 43.6 3145 1900 2.1 3971

Pit 8 18.2 1314 800 2.1 1663

Pit 9 17.3 1249 800 2.0 1604

Pit 10 8.9 645 400 2.1 820

Pit 11 160.0 11553 6800 2.2 15254

Pit 12 369.0 26644 38000 2.3 88131

Pit 13 65.6 4737 2800 2.1 5943

Pit 14 83.6 6036 3600 2.1 7593

Pit 15 219.0 15813 12000 2.1 25616

6.4.2.2 Mine Site Sediment Pond Management

The in-pit sediment ponds will be used opportunistically to meet local demand for water (e.g. dust suppression) thereby reducing the need for supply from other sources (e.g. shallow aquifer bores). For the dual purposes of containing sediment on site for controlled disposal and for providing low quality water supply, sediment and erosion control measures will include:

regular inspection of the in-pit sediment storage structures conducted at the conclusion of the wet

season (typically in April-May).

monitoring of sediment deposition volumes and identification if a clean out is required to provide

sufficient storage for sediment loading in runoff and improve storage availability where in-pit

sediment ponds are in use for dust suppression.


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Clean out of in-pit sediment ponds will be completed immediately prior to the wet season, and sediment will be disposed of in a location where erosion will be limited or contained (e.g. mining areas undergoing rehabilitation), and will not contribute to sediment loads reporting to other control structures.

6.4.3 Port Infrastructure Area

6.4.3.1 Overview

A new sediment pond will be required at the Port infrastructure area, in addition to the existing sediment pond (which will be retained) to capture runoff from disturbance areas, including the bauxite stockpile, paved areas, workshops and haul roads. The proposed and existing sediment ponds are shown in Figure 6-1, which also shows runoff flow paths and drainage control structures.

The existing sediment pond will capture runoff from a smaller area than the area for kaolin mine activities only. The proposed sediment pond will absorb some of the catchment of the existing sediment pond and capture runoff from the bauxite stockpile area.

Based on a preliminary risk assessment (Section 6.4.3.13), the proposed Port area sediment pond is not expected to be a regulated dam. Following detailed design, and prior to the design and construction of the structure, the Port area sediment pond will be subject to a regulated dam assessment by a suitably qualified and experienced person in accordance with the Manual for Assessing Consequence Categories and Hydraulic Performance of Structures (EHP, 2014). A consequence assessment report and certification will be prepared for each structure assessed.

Port sediment pond conceptual engineering design has been undertaken to understand the performance of the dams in managing sediment in Port infrastructure area. The key issues in the design of the sediment ponds are:

pond catchment size and size of ponds

natural of material resulting in sediment (i.e. particle size, clay content) within each catchment

engineering design standards for sediment ponds

distinction between operational periods (i.e. April to December) and non-operational periods (wet

season shut down January to March) for sediment management.

The assessment of the Port sediment pond below supercedes any information provided in Appendix 4 on Port sediment pond design.

6.4.3.2 Pond Sizing and Catchments

The pond catchment sizes and dam volumes are:

8 ha for the proposed pond, with a volume of 9 ML

5 ha for the existing pond, with a pond volume of 6 ML.

The existing pond catchment has been reduced from its current catchment size as some of the catchment has been diverted to the proposed pond. Pond catchments and drainage control are shown in Figure 6-1.

These pond catchment sizes should be viewed in the context of the Skardon River catchment of 48,000 ha (i.e. 0.03% of the Skardon River catchment).

The catchments of the Port sediment ponds will be modified and constructed landscapes, comprising hard stand areas and compacted roads. The proposed sediment pond catchment will contain:

bauxite stockpile pad comprising of laterite (ironstone) and low grade bauxite material


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bauxite stockpile, comprising un-beneficiated bauxite during the operational period and reduced to

no bauxite during the wet season closure

haul road loop with ironstone as the top capping, and fill materials of laterite and low grade bauxite

excavated from mining

hard stand infrastructure areas comprising of laterite (ironstone) and low grade bauxite material.

Therefore, within the catchment of the Port sediment ponds there will minimal areas of unmodified landscape or areas where vegetation or soils have been removed but not resurfaced with laterite (ironstone) or bauxite.

6.4.3.3 Sediment Type within Pond Catchments

Particle size distribution for bauxite material has been estimated in Appendix 4. In summary, the particle size distribution for three samples analysed had a D10 of approximately 0.05 mm (10% of the particle sizes are smaller than 0.05mm), and hence it is assumed that 90% by weight of the sediment to be managed will be ≥0.05 mm.

Geological information from bauxite resource sampling indicates that the bauxite stockpile will most likely contain bauxite with low clay content (deposit average reactive silicon dioxide SiO2 of 6%). Water flow to the sediment pond is therefore likely to be a clay poor material and more likely to comprise remnant bauxite pisolites or laterite nodules.

Information on topsoils in the Project area (Chapter 7) indicate that these materials are not sodic and therefore not dispersive (sandy soils to clay loam soils). However as noted, the catchments of the Port sediment ponds are not expected to contain this material. Natural soil types at the Port are mapped as the Weipa soil group, described as deep gradational or uniform red massive soil with aluminous concretions, predominantly sandy topsoils, but clay containing topsoils are described in the area (clay loams). However, the regional geology is mainly of clays, particularly for subsoils and the sedimentary sequence described for the Weipa Plateau (Chapter 10). Information from the drilling program indicates increasing clay soils towards the Skardon River. Given the material types and geology of the project are is not expected that materials will be dispersive. It has been assumed that some clay materials will be present in the catchments reporting to the sediment ponds.

6.4.3.4 Engineering Design Standards

Under the International Erosion Control Association (IECA) Manual (IECA, 2008), there are different design standards for sediment ponds depending on particle size and dispersiveness summarised in the table below.

The material reporting to sediment ponds will likely be considered self-settling within any sediment basin, and based on the likely sediment size would require a Type C basin, under the IECA Manual,


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which state that where the D33 > 0.02mm (i.e. 67% of samples greater than 0.02mm) a Type C basin is required, if <10% of soil is dispersive. As noted above 90% of sediment is estimated to be greater than 0.05mm, and therefore it is true that 90% of sediment is estimated to be greater than 0.02mm. IECA (2008) also provide for a Type D basin to be used for turbidity control, even where material is non-dispersive.

6.4.3.5 Sediment Management – Wet Season and Operational Period

Sediment management is differentiated between wet season closure period and dry season operational period. During the operational period there will be activities that may result in sedimentation including use of haul roads, use of infrastructure areas and bauxite stacking, transfer, stockpiling and loading. However, this is the period of least rainfall and the period in which controlled releases can occur when water quality criteria are achieved (refer to Chapter 17 for Port sediment dam release criteria). Controlled release occurs once sediments have either been flocculated and / or settled out. Release water quality criteria area described in Chapter 17 as release water quality is linked to water quality in the marine / estuarine environment of the Skardon River.

During the operational period, it is expected that sediment will be removed annually (likely October / November) when ponds have naturally dried out due to evaporation. In December, at the start of the wet season the ponds will have maximum storage capacity, including the sediment storage zone. Sediment that is removed will be taken to an area where sediments will be contained, such as a mining area prior to rehabilitation.

During the wet season, the bauxite stockpile will be reduced to zero (hardstand stockpile pad remains) and there will be no haul truck movements. Therefore, activities resulting in sedimentation are substantially reduced. During this period there may be overflows from the Port sediment ponds once water from the pond has passed through the sediment ponds. At the start of the operational period, any runoff from the catchment zones would have minimal sediment as it would have been captured during the wet season.

As such, the sediment ponds have been designed to a Type D level, to provide for turbidity control during the operational period each year, when vehicle movements and ground disturbance are occurring, when the product stockpile pad is in use. A Type D basin has a larger storage volume than a Type C basin.

The conceptual design of a Type D sediment basin is shown in the figure below, which shows the sediment storage zone and the settling zone.


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Once operations cease for the year, and the product pad is cleared, a final first flush rainfall event (or a series of smaller events) will clean off the residual material over the Port area to the sediment ponds. After this event, when disturbance within the sediment pond catchments at the Port is minimal, and without product stockpile material present, the sediment basins will operate as Type F/C basins, treating runoff from the Port area catchment which has lower sediment content than the operational period. The sediment ponds would be expected to quickly settle out the coarser fractions for the whole year.

6.4.3.6 Bauxite Stockpile Sediment Control

The stockpile will be gradually depleted over the year and decreased to zero prior to January so that no stocks are held during the wet season. This will prevent runoff from the stockpile over the wet season. Never-the-less the stockpile will be bunded and any runoff from the bauxite stockpile will be directed towards a sediment trap / sediment check dam system. This will consist of drains, incorporating rock lining as required, around the bauxite stockpile which direct runoff to an interceptor system. Sediment from the interceptor will be removed regularly, including after significant rainfall events. Outflow from the interceptor system will be directed to the port sediment ponds, thereby reducing the volume of sediment reporting to the sediment ponds.

6.4.3.7 Contaminant Management

Measures to prevent contamination of surface water and groundwater from hydrocarbons and chemicals in infrastructure areas, and from the landfill and bio-remediation pad are described in Chapter 11. Waste management at the Port infrastructure area is described in Chapter 8. The landfill and bio-remediation pad will be bunded to prevent ingress of runoff and prevent outflow of potentially contaminated water from direct rainfall.

These measures (e.g. bunded storage areas, interceptors, oily water separators, etc) are intended to prevent runoff to sediment ponds containing hydrocarbons, chemicals and other pollutants. Therefore, any releases from the sediment ponds are not expected to contain elevated levels of hydrocarbons or chemicals.

6.4.3.8 Modelling of Pond Capacity

A design for the proposed sediment pond has been prepared consistent with the IECA Manual, the accepted guideline document for sediment basin design within Queensland. The design is specifically for a basin with a design life > 6 months, discharging to sensitive waters, based on the 85th percentile, 5 day storm. This means that 85% of all events can be accommodated by the structure, allowing for 5 days to settle and discharge waters after the event. This is greater than the standard design based on the 75th percentile.

A daily water balance model was developed to test the operation of the basin. The model was developed as follows:

Daily rainfall was utilised from 1914 to 2016, derived from BOM station 027071 (Skardon River),

infilled by stations 027045 (Weipa Aero) and 027042 (Weipa Eastern Ave).

The AWBM was utilised to derive daily runoff from rainfall, adopting a Cavg = 35.4, BFI = 0, Kb = 1,

Sb = 0.1 and other values as per Boughton & Chiew (2003). This produced a daily runoff series, from

1914 to 2016, in mm, which when applied to the catchment area gave daily flow into the basin.

The runoff was routed through the basin, utilising the storage volumes calculated in the design.

Evaporation was extracted from the dam, and rainfall added.

Operating rules were applied, whereby:

Controlled releases were only undertaken during the operational window, April – December.


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A controlled release event was triggered where the volume was above the sediment storage

volume, and where rainfall had essentially stopped (i.e. where rainfall dropped below

5mm/day).

A 5-day window was used post rainfall to allow for full capture, settlement and pumping out.

Pump out began on the 3rd consecutive day following no rainfall and continued until the 5th

Pump out only affected the settling zone – the sediment storage zone was not removed to allow

for stored sediment to remain. This is conservative as it assumes sediment is occupying

sediment storage zone and this is not the case, particularly at the beginning of the operational

season when less sediment is present.

The data was analysed in terms of total number of overflow events per year, from 1914 to 2016, during the operational period. Closer examination of some months was made to better understand the model results.

The model setup (and the design itself) is highly conservative, as controlled release of water will create storage to the level of the settled material, rather than only to the top of the sediment storage zone. Also, the two days allowed for flocculation and settlement is also expected to be conservative, since most of the material is expected to be coarse rather than fine.

The results show an average of 1.3 overflow events during the operational period (i.e. April to December) each year, with a maximum of 3 discrete events in any one year (model year 2010). An average of 0.7 overflow events per year were recorded in April and 0.6 events per year for December. Between May and November, overflows are virtually eliminated, with only 6 years modelled with overflows in 102 years.

During April, when operations are starting the catchment contains limited fine sediment. In December, the pond will have been emptied of sediment empty, the product stockpile would be approaching zero volume and a first flush rainfall event would have reported to the sediment pond. During overflow events in April and December, the sediment pond will operate as essentially an oversized Type C basin, and provide substantial treatment during all periods as all runoff is passing through the pond.

If the first 2 weeks of April are not considered ‘operational’ due to late wet season rainfall, then the model predicts that overflows in April during operational periods would be reduced to 1 in every 6.9 years. Similarly, if the last 2 weeks of December are not considered operational due to early onset of the wet season, then overflows in December during operational periods would be reduced to 1 in every 7.4 years.

During the wet season period (modelled as January to March), the sediment pond will also operate as essentially an oversized Type C basin, and provide substantial treatment during all periods as all runoff is passing through the pond. During the wet season period there will be overflows from the pond.

The model does not factor in additional control measures that can be implemented for sediment control for overflow events during April and December. Controls which can be implemented to reduce overflows include shortening the time required to remove waters prior to the next storm by using better flocculation techniques, and by pre-empting wet conditions in releasing from the pond. Any overflows will still be subject to treatment within the sediment ponds, with flocculation and simple sedimentation (without flocculation) resulting substantial treatment even with overflow of the basin. Deatiled design may result in the inclusion of multiple divisions within the sediment pond, if required to improve sediment control.

As a means to test additional control, model assumptions were amended for more proactive management, by allowing for pumping to begin after 24 hours of no rainfall, and to remove water within


Page 6-11

2 days rather than 3. This reduced overflow events in April to an average of 0.5 per year, and overflow events in December to 0.4 per year.

The nature of the model means that the number of overflow events is over estimated, since a single event with a 1 day gap in the middle is counted as 2 events, and drawdown into the sediment storage zone will in reality be possible during both April and December.

6.4.3.9 Release Management

The sediment ponds will incorporate overflow weirs, overflow drainage stabilised structures, and flow spreaders to ensure that no erosion is caused by discharge events (overflows or controlled release). Frequent inspections of the drainage structures will be undertaken to provide early warning of any issues requiring rectification. A detailed inspection of all drainage structures (and the pond integrity) will also be undertaken each dry season.

The overflow point of the proposed sediment pond is located at least 100 m from the mangroves and 150 m from the Skardon River and flows through Eucalyptus tetrodonta woodland. Water will spread over this grassed native vegetation area resulting in dissipation of flows and a reduction in velocity and erosion potential.

Overflow events will occur during wet season rainfall events that exceed the design capacity of the sediment ponds, when there are expected to be naturally high levels of turbidity in the receiving environment. Port area sediment ponds will minimise impacts on the Skardon River by:

discharging through the nominated overflow weir

managing releases to prevent scouring (e.g. rock spillways)

maximising the distance through which discharges flow through vegetation prior to entering the

Skardon River, thereby allowing for additional sediment control.

Given the scale of the estuary compared to the scale of the catchments of the Port area sediment ponds, and high natural variation in estuary turbidity, any releases from the sediment pond are likely to have a minimal impact on the marine environment. The monitoring program for releases from the Port sediment ponds is designed to identify potential impacts from releases, and is described in Chapter 17.

6.4.3.10 Existing Sediment Pond Design

A design was also undertaken for the existing sediment pond, finding that the existing capacity is sufficient to the level of the same design criteria as for the proposed pond. Overflow events are similar to the other basin (1.5 average overflow events per year between April and December). This does not equate to 2.8 events per year (1.3 for new pond + 1.5 for existing pond) but 1.5 events, since both will be discharging during high rainfall events. Note however that the existing pond will be draining Port hardstand areas, excluding major haul roads and the product stockpile area. As such, runoff is anticipated to be contain less sediment than the new pond, and so the small additional overflow frequency is not considered significant. Both ponds are considered to be equal in level of sediment treatment provided.

The release point from the existing sediment pond is located approximately 200 m from the Skardon River, at a point where there are almost no mangrove communities, and flows through Eucalyptus tetrodonta woodland. Water will spread over this grassed native vegetation area resulting in dissipation of flows and a reduction in velocity and erosion potential.

6.4.3.11 Design Features

Detailed design of the Port area sediment ponds will be done by an appropriately qualified person, considering the design standards described above.


Page 6-12

Port sediment ponds will be located above the 1:100 year flood level for the Skardon River as described in Chapter 14.

The pond(s) will not be more than 10 m in height and hence will not require a failure impact assessment under the Water Supply (Safety and Reliability) Act 2008.

The proposed stormwater management at the Port will also meet the following design and management measures:

Erosion protection and sediment control measures will be installed and maintained for all stages of

the activity to minimise erosion and the release of sediments.

All areas of soil disturbed and exposed will be managed to minimise the loss of sediment through

revegetation and/or use of other stabilisation techniques (i.e. hardstand areas).

All concentrated stormwater flows (including ‘clean’ stormwater and ‘dirty’ stormwater) will have

concentrated flow paths, such as the proposed drainage control structures, which have been

designed, constructed, effectively armoured and maintained to convey the runoff without causing

water contamination, sheet, rill or gully erosion, sedimentation, or damage to structures or

property.

Stormwater runoff from external or undisturbed catchments will be diverted around or away from

disturbed areas as much as possible.

6.4.3.12 Release Monitoring

Port sediment pond release monitoring, including contaminant release limits, are described in Chapter 17 as release limits are based on estuarine water quality data from the Skardon River, as presented in Chapter 17.

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Figure 6-1

LegendMining Lease BoundariesPort Infrastructure Area

Port LayoutDrainage ControlPond Catchment

!>Port Area Sediment DamRelease PointsConceptual OverlandFlow Path0.5m Contours

G:\CLIENTS\E-TO-M\Gulf Alumina\GIS\Maps\EIS\Ch06_Water_Mgmt\FIG_06_01_Port_Layout_Conceptual_Flow_160311.mxd

Revision: R1

Date: 15/03/2016 Author: malcolm.nunn1:6,000Map Scale:

Coordinate System: GDA 1994 MGA Zone 54

Port Area Sediment Pondsand Drainage

0 50 100 150 200 250Meters

Gulf Alumina Limited

No warranty is given in relation to the data (including accuracy, reliability, completeness or suitability) and accept no liability (including without limitation, liability in negligence) for any loss, damage or costs (including consequential damage) relating to any use of or reliance upon the data. Data must not be used for direct marketing or be used in breach of privacy laws.Imagery supplied by Gulf Alumina (2014). Tenures © Geos Mining (2015). State Boundaries and Towns © Geoscience Australia (2006).

±

*Port/Wharf infrastructure are indicative layouts only and adapted from plans created by Sedgman Ltd.Pond catchments and drainage are indicative and based on plans created by Sedgman Ltd.


Page 6-14

6.4.3.13 Preliminary Regulated Dam Assessment

The proposed Port area sediment pond has been located such that no dwellings or workplaces are located within the potential failure impact zone. There are no other structures proposed downstream of the Port area sediment pond that would result in a cascading failure. There are no drinking water sources downstream of the Port area sediment ponds. There are no contaminants (e.g. hydrocarbons) that will be released from Port sediment ponds (sediment is not considered to be a contaminant) as these have their own management systems within the Port infrastructure area.

This area is already subject to disturbance from Port development and will be subject to further disturbance through wharf construction and ship operations for the Project. There are no known seagrass communities in the area near the Port proposed for the wharf and limited fringing mangrove vegetation due to the relatively steep topography of the Port area.

A preliminary consequence category assessment, based on the Manual, is provided in Table 6-2. This assessment is preliminary in nature as the final detailed design of the proposed Port sediment pond has not been completed. A final consequence category assessment will be undertaken once detailed design is sufficiently progressed.

The consequence category has been assessed as low for all failure event scenarios. Therefore, the proposed Port area sediment pond has not been assessed as a regulated structure.

Table 6-2 Preliminary Consequence Category Assessment

Scenario Failure to Contain: seepage

Failure to contain: overtopping

Dam Break

Harm to humans: dam break

n/a n/a Low - Location such that people are not routinely present in the failure path and loss of life is not expected.

Harm to humans Low - Location such that contamination of waters (surface and/or groundwater used for human consumption could result in the health of less than 10 people being affected. There are no known human consumptive uses of downstream surface water or groundwater.

General environmental harm

Low – Contaminants are unlikely to be released (other than sediment) and even if contaminants are released to areas of Significant Values or Moderate Values, they would be unlikely to meet any of the following minimum thresholds:

i) Loss or damage or remedial costs greater than $10 million

ii) Remediation of damage is likely to take more than 6 months

iii) Significant alteration to existing ecosystems

iv) The area of damage (including downstream effects) is likely to be greater than 1 km2.

General economic loss or property damage

Low - Location such that harm to third party assets in the failure path would be expected to require less than $1 million in rehabilitation, compensation, repair or rectification costs.

Any structures that may require a consequence category assessment will be assessed by a suitably qualified and experienced person in accordance with the Manual prior to the design and construction of


Page 6-15

the structure. A consequence assessment report and certification will be prepared for each structure assessed.

It is anticipated that all structures required for the Project will have a low consequence category rating with respect to the seepage, overtopping and dam break criteria and hence will not be regulated structures. Therefore, management measures have not been proposed for regulated structures. However, should any structure be found to be requiring categorisation as a regulated structures, the proponent will seek approval for those structures prior to construction. Any management measures related to regulated structures will be based on the Guideline for Dams or Levees.

As per the Guideline for Dams or Levees:

Where a structure is assessed as a low consequence structure, and later assessment results in the

structure being determined to be a significant or high consequence category structure, this will

require an amendment to the existing environmental authority or the Register of Regulated Dams.

The consequence category of any structure must be assessed by a suitably qualified and

experienced person in accordance with the Manual for Assessing Consequence Categories and

Hydraulic Performance of Structures (EM635) at the following times:

a) prior to the design and construction of the structure, if it is not an existing structure; or

b) if it is an existing structure, prior to the adoption of this schedule; or

c) prior to any change in its purpose or the nature of its stored contents.

In consideration of the above assessment that there are no proposed regulated dams for the Project, and that the assessment is preliminary until detailed design is completed, the following EA conditions are proposed in relation to regulated dams:

(X1) The consequence category of any proposed structure must be assessed by a suitably qualified and experienced person in accordance with the Manual for Assessing Consequence Categories and Hydraulic Performance of Structures (EM635) at the following times:

a) prior to the design and construction of the structure, if it is not an existing structure; or

b) if it is an existing structure, prior to the adoption of this schedule; or

c) prior to any change in its purpose or the nature of its stored contents.

(X2) A consequence assessment report and certification must be prepared for each structure assessed and the report may include a consequence assessment for more than one structure.

(X3) Certification must be provided by the suitably qualified and experienced person who undertook the assessment, in the form set out in the Manual for Assessing Consequence Categories and Hydraulic Performance of Structures (EM635).

(X4) If the assessment under (X1) determines that any proposed structure is a regulated structure than environmental authority holder cannot construct or operate that structure until this environmental authority has been amended to include conditions related to the design, construction, operation, mandatory reporting level, design storage allowance, annual inspection, decommissioning, rehabilitation and register of regulated dams, as authorised by the administering authority.

6.4.4 Erosion and Sediment Control

Other than the Port infrastructure area and mining areas, erosion and sediment control measures will be implemented at:

construction areas

permanent haul roads


Page 6-16

haul road crossing of Namaleta Creek and other drainage features.

6.4.4.1 Erosion and Sediment Control Plan

An erosion and sediment control plan (ESCP) will be developed for the Project prior to commencement of construction and mining activities and will cover all aspects of the Project including clearing, construction, operations, rehabilitation and decommissioning. The ESCP will be approved by a suitably qualified person (such as a Certified Professional in Erosion and Sediment Control).

An ESCP will be developed in accordance with the:

recommended guidelines of the International Erosion Control Association (IECA) Manual (IECA,

2008)

Soil Erosion and Sediment Control-Engineering Guidelines for Queensland Construction Sites

(Witheridge and Walker, 1996)

The ESCP will include the following:

An assessment of erosion risk will be undertaken for different parts of the Project area.

Soil types will be assessed (refer Chapter 10), including identification of erosion potential.

Soil will be managed in accordance with the measures described in Chapter 10 for soil stripping,

handling, stockpiling and testing.

Development of the ESCP will be integrated into the mine planning process.

Sensitive areas (e.g. buffer zones around watercourses and wetlands) that may require specific

measures to prevent sedimentation will be identified.

The period of maximum disturbance will be planned to occur in the dry season.

Construction activities and land clearing will be undertaken in the dry season.

The extent and duration of disturbance (topsoil and subsoil exposure) will be minimised.

Boundaries of areas to be cleared will be delineated and clearing will be authorised by use of a

‘permit to clear’ system.

Grubbing out and removal of ground cover will be carried out as close to the time of mining or

earthworks as possible.

Stabilisation of areas cleared in advance of mining will occur through allowing regrowth of grasses

and shrubs.

Stormwater runoff from external or undisturbed catchments will be diverted around or away from

infrastructure construction areas.

Uncontaminated stormwater run-off will be diverted around areas disturbed by Port infrastructure

area activities or where contaminants or wastes are stored or handled.

All drainage structures and sediment controls will have design specifications appropriate to the

rainfall regime and design life.

Erosion controls will be used to minimise sediment generation and transport.

Sediment controls will be used to treat run-off from disturbed areas prior to leaving the site.

Sediment controls will be located as close to the source as possible.

Erosion and sediment control structures will be installed as required, prior to disturbance in that

area of site.

Disturbed areas will be stabilised as soon as possible (progressively rehabilitated).

Control structures will be inspected regularly.


Page 6-17

Details of the rehabilitation of the site, including final landform design is provided in Chapter 7. Rehabilitated landforms will be designed to minimise slope angle and length. Erosion loss decreases exponentially with percentage ground cover and is greatly reduced when cover exceeds 50%. For long-term stabilisation in tropical climates, IECA (2008) recommends a minimum ground cover of 80% which will be considered as the target for this Project. Vegetation establishment will be required for long-term soil stabilisation. All revegetated areas will be monitored to ensure the desired ground cover is achieved and further seeding or planting is conducted in areas that do not meet the desired target.

Erosion mitigation measures specifically relevant to waterways include the following:

Where earthworks are carried out in proximity to a watercourse, disturbance will be stabilised.

Felled timber will be removed from the area and stockpiled away from the watercourse.

Where required temporary controls will be installed along cleared slopes approaching watercourses,

to divert dirty water away from the watercourse.

Clean rock and culverts will be used for temporary watercourse crossings

Water discharged to a waterway will meet Project water quality objectives.

The ESCP may include measures such as:

velocity slowing methods including rock and log placement in cleared areas

restriction of land disturbance

scour protection design methods for drainage

rehabilitation practices to limit erosion.

The ESCP will be implemented for construction and throughout operations. Drainage and erosion control will be implemented as a part of operational activities using measures such as erosion control blankets, check dams, filter fences and rock mattresses.

Monitoring of erosion and sediment control structures will be carried out both pre- and post-wet season and following any significant events. Monitoring may be done using visual methods (such as those for recording erosion features) and/or more quantitative methods such as those using erosion monitoring pins, or measuring sediment loads from monitored catchments.

Monitoring of erosion and sediment controls may include:

visual inspections undertaken regularly and following significant rainfall e.g. 20 mm in 24 hours

daily monitoring of weather predictions to manage clearing and construction activities.

completion of site inspection checklist

supervisors to visually monitor all operations and identify where correct procedures are not being

followed

contractors to monitor works and should they become aware of improper management practices, to

report the issue to their supervisor.

site supervisors will be responsible for modifying or stopping non-conforming management

practices until corrective actions are determined

corrective and preventive actions to be implemented and monitored visually on site to ensure they

are effective.

6.4.4.2 Permanent Haul Roads

Permanent haul roads (i.e. the main haul road connecting the Port area to the mining areas to the south) will be designed in consideration of the Department of Transport and Main Road’s (TMR’s) Road


Page 6-18

Drainage Manual (TMR, 2015). This provides technical guidance on road drainage, erosion, environmental and sediment control.

6.4.5 Namaleta Creek Crossing

6.4.5.1 Location

The location of the proposed crossing of Namaleta Creek is shown in Figure 6-2. This is the same location as the existing crossing.

6.4.5.2 Existing Crossing

The existing crossing of Namaleta Creek crossing consists of an earthen crossing (10 – 15 m wide), where two cylindrical pipes connect the upstream and downstream reaches of Namaleta Creek. These existing pipe culverts may be impacting flows and fish passage. The section of road currently crossing the south-western flood plain of Namaleta Creek (refer to Figure 6-2) may be restricting normal flow during the height of the wet season.

Namaleta CreekCrossing

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Figure 6-2

G:\CLIENTS\E-TO-M\Gulf Alumina\GIS\Maps\EIS\Ch06_Water_Mgmt\FIG_06_02_Namaleta_Crossing_Contours_WWBW_160311.mxd

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Namaleta Creek Crossing Location

0 50 100 150 200Meters


!

!

!

!

Queensland

CAIRNS

BRISBANE

TOWNSVILLE

ROCKHAMPTON

±

No warranty is given in relation to the data (including accuracy, reliability, completeness or suitability) and accept no liability (including without limitation, liability in negligence) for any loss, damage or costs (including consequential damage) relating to any use of or reliance upon the data. Data must not be used for direct marketing or be used in breach of privacy laws. Tenures © Geos Mining (2015). State Boundaries and Towns © Geoscience Australia (2006). Watercourses © Geoscience Australia. Imagery sourced from Gulf Alumina. Waterways for Waterway Barrierworks © State of Queensland (Department of Agriculture and Fisheries) 2015.

Legend!( Port of Skardon River

Mining Lease BoundariesWatercoursesExisting Disturbance FootprintProject Footprint

Haul RoadCrossingElevation Contours (0.5m)

Queensland Waterways forWaterway Barrier WorksRisk of Impact

2 - Moderate (Streams)

*Haul Road/Crossing layouts are indicative only and based on centrelines in plans created by Sedgman Ltd.


Page 6-20

6.4.5.3 Crossing Design

The crossing will be upgraded to support haul truck movements between mining areas to the south of Namaleta Creek and the Port. The corridor associated with the proposed upgrade of the crossing will be 25 m wide, except for the section requiring culverts, which may have a construction width of 60 m (culvert width approximately 40 m) as shown in Figure 6-2.. The design of the crossing will be in accordance with the Department of Agriculture and Fisheries Code for Self-assessable Development – Minor Waterway Barrier Works, Part 3 Culvert Crossings, Code Number: WWBW01 April 2013 (the Code). This Code is designed to minimise impacts to fish passage. In this respect the upgraded crossing will result in the hydrology of the area more closely resembling its pre-disturbance condition.

Conceptual design schematics for the Namaleta Crossing are presented in the figures below:

Schematic 1 shows the crossing layout as per Figure 6-2, including chainage from the northern side

of the crossing (i.e. near the kaolin pits) on the left (chainage = 0 to the end of the floodplain to the

south (chainage 494).

Schematic 2 shows the longitudinal plan with chainage 0 on the left and chainage 300 on the right,

which due to the scale, condenses the width of the culverts. As can be seem in Schematic 2, the

crossing height is at its maximum in the centre of the channel crossing, allowing for control of runoff

control away from the Creek.

Schematic 3 continues from the previous schematic and shows the longitudinal plan with chainage

300 on the left and chainage 494 on the right.

Schematic 4 shows a cross section through the portion of the crossing with the main flow path

channel of Namaleta Creek.


Page 6-21

Schematic 1 – Crossing Layout


Page 6-22

Schematic 2 – Longitudinal Plan – Chainage 0 to Chainage 300

Schematic 3 – Longitudinal Plan – Chainage 300 to Chainage 494


Page 6-23

Schematic 4 – Cross Section in Creek Channel


Page 6-24

Chapter 14 describes the crossing design for the purpose of flood protection. This flood protection has been adopted in the conceptual engineering schematics shown above. A schematic cross-section of the Namaleta Creek crossing, for the purposes of modelling flood protection, is shown in Figure 6-3. The culverts and deck level of the crossing were sized for a 1:50 year AEP design flood standard. The flood model in Chapter 14 also demonstrates that the haul road crossing will meet a design flood level of 1:100 years (i.e. the haul road crossing will not be overtopped by a 1:100 year flood). Figure 6-3 shows the preliminary sizings of the culvert groupings proposed to convey water through the haul crossing embankment, as applied in the model. Note that the culverts are distorted by the aspect ratio of the cross-section.

Figure 6-3 Namaleta Creek Crossing – Downstream View

Preliminary sizing of the culvert groups and bridge deck level required at the crossing was carried out with reference to the guidelines and recommendations of the Road Drainage Manual, Department of Transport and Main Roads, July 2015 (TMR-RDM).

Detailed design will be carried out in compliance with the TMR-RDM and with:

Roads in the Wet Tropics Manual, Transport and Main Roads, (1998)

design detail requirements of the Code for Self-Assessable Development; Minor Waterway Barrier

Works Part 3: Culvert Crossings, Code number: WWWBW01 (April 2013), Department of Agriculture,

Fisheries and Forestry (DAFF).

The following specific conditions are noted from the Code for addressing moderate impact waterways (applicable to Namaleta Creek):

Works must commence and finish within a maximum time of 360 calendar days and instream

sediment and instream silt control measures associated with the works must be removed within this

period.

The crossing must have a minimum (combined) culvert aperture width of 2.4 m or span 100% of the

main channel width.

All new or replacement culvert cells must be installed at or below bed level.

The internal roof of the culverts must be >300 mm above ‘the commence to flow’ water level.

Where the cell is installed at less than 300 mm below bed level (potentially the case for the

Namaleta Crossing), the culvert floor must be roughened throughout to approximately simulate

natural bed conditions.

The culvert must be installed at no steeper gradient than the waterway bed gradient.


Page 6-25

Apron and stream bed scour protection must be provided in line with the design requirements of

the Code.

Based on conceptual design of the crossing presented in the above schematics, it is expected that the Code requirements can be met for the Namaleta crossing design.

6.4.5.4 Crossing Drainage

Drainage from road surface of the crossing will be directed to the ends away from the Creek, by peaking the height of the crossing at its centre and raising the entire crossing above the elevation of the surrounding topography. Thus stormwater runoff will drain to the entry points of the crossing approximately 50 m to 100 m from the Creek bank. Silt traps will be installed at the end of the drains and over flow directed into contour drains. On the south-west side this water will flow into natural vegetation while on the north-east side water will be directed into kaolin mine revegetation areas, or kaolin mine water storages.

6.4.5.5 Crossing Construction and Rehabilitation

To prevent any instream impacts including sedimentation to Namaleta Creek and the mapped HES wetland during the construction of haul road crossing, construction activities will be scheduled for the dry season, when the potential for impact is minimised due to low or no flow conditions when temporary impoundments are not expected to be required when working within the in-stream environments. This strategy is also part of avoiding disturbance of acid sulphate soil, the management of which is described in Chapter 10.

With construction of the proposed crossing within a single dry season, temporary changes to the drainage and flow regimes will be avoided and Creek flow will be improved from the current situation in the following wet season. Construction work within Namaleta Creek will ensure that all surfaces are adequately stabilised following the completion of the haul road crossing. This will include revegetation of exposed embankment areas and mulching if necessary until stream banks have stabilised.

The crossing will be constructed with ironstone material from the borrow pits over a claystone core, using material from the kaolin claystone overburden stockpile. The claystone core material will not be exposed to erosion, with batter protection being provided through concrete, rock and / or geofabric, and material encased by ironstone and waste bauxite material.

6.4.6 Crossings of other Drainage Features

The haul road will cross a drainage feature between Pits 14 and 15 to the south of Namaleta Creek (referred to as Tributary 1), as shown in Figure 6-4. This drainage feature is mapped as moderate risk for waterway barrier works. Mining is not scheduled south of this crossing (i.e. when the crossing will be required) until Year 7 of mining. The design of the crossing will be in accordance with the Department of Agriculture and Fisheries Code for Self-assessable Development – Minor Waterway Barrier Works, Part 4 Bed Level Crossings, Code Number: WWBW01 April 2013.

The conceptual design of the crossing is shown in the schematics below:

Schematic 5 shows the crossing layout as per Figure 6-4, including chainage from the northern side

of the crossing (chainage 0) to the southern side (chainage 240).

Schematic 6 shows the longitudinal plan with chainage 0 on the left and chainage 240 on the right.

Schematic 5 – Tributary 1 Crossing Layout


Page 6-26


Page 6-27

Schematic 6 – Tributary 1 Crossing Longitudinal Plan


Page 6-28

All works required within the drainage feature will ensure that all surfaces are adequately stabilised following the completion of the haul road construction. This will include revegetation of exposed embankment areas and temporary erosion and sediment control until construction is completed or drainage feature banks have been stabilised.

The following specific conditions are noted from the Code for addressing moderate impact waterways (applicable to Tributary 1 crossing):

The bed level crossing must be no greater than 15 metres wide in an upstream/downstream

direction (not including stream bed scour protection).

New bed level crossings must be aligned perpendicular (within 10°) to the water flow.

Where the bed level crossing is to be constructed from rocks, use clean rocks (minimal fine material)

that are an equivalent or larger size than the natural bed material at the site, and at least 50 mm

diameter.

Stream bed scour protection must be provided in line with the design requirements of the Code.

Works must commence and finish within a maximum time of 360 calendar days and instream

sediment and silt control measures associated with the works must be removed within this period.

The lowest point of the bed level crossing must be installed at the level of the lowest point of the

natural stream bed (pre-construction), within the footprint of the proposed crossing.

There must be a height difference of at least 100 mm from the lowest point of the crossing to the

edges of the low flow section of the crossing.

If the crossing is constructed from concrete or introduced rock, the level of the remainder of the

crossing must be no higher than the lowest point of the natural stream bed outside of the low flow

channel.

If the crossing is constructed from the natural bed material, the level of the remainder of the

crossing must be no higher than the highest point of the natural stream bed outside the low flow

channel.

Based on conceptual design of the crossing presented in the above schematics, it is expected that the Code requirements can be met for the Tributary 1 crossing design.

Drainage FeatureCrossing

Pit #14

Pit #15

Pit #15

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Figure 6-4

G:\CLIENTS\E-TO-M\Gulf Alumina\GIS\Maps\EIS\Ch06_Water_Mgmt\FIG_06_04_Drainage_Crossing_Contours_WWBW_160311.mxd

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Haul Road Crossing ofDrainage Features

0 50 100 150 200Meters


!

!

!

!

Queensland

CAIRNS

BRISBANE

TOWNSVILLE

ROCKHAMPTON

±

No warranty is given in relation to the data (including accuracy, reliability, completeness or suitability) and accept no liability (including without limitation, liability in negligence) for any loss, damage or costs (including consequential damage) relating to any use of or reliance upon the data. Data must not be used for direct marketing or be used in breach of privacy laws. Tenures © Geos Mining (2015). State Boundaries and Towns © Geoscience Australia (2006). Watercourses © Geoscience Australia. Imagery sourced from Gulf Alumina. Waterways for Waterway Barrierworks © State of Queensland (Department of Agriculture and Fisheries) 2015.

Legend!( Port of Skardon River

Mining Lease BoundariesWatercoursesExisting Disturbance FootprintProject Footprint

Haul RoadCrossingElevation Contours (0.5m)

Queensland Waterways forWaterway Barrier WorksRisk of Impact

2 - Moderate (Streams)

*Haul Road/Crossing layouts are indicative only and based on centrelines in plans created by Sedgman Ltd.


Page 6-30

6.4.7 Operation of the Water Management System

6.4.7.1 Responsibility

Water management issues traditionally cross over a number of organisational boundaries within an operation. It is therefore important to clearly assign responsibilities for all aspects of water management to specific roles from senior management to the operator level. Gulf Alumina will assign responsibilities appropriately in line with operational development. Responsibilities with respect to water management include:

day-to-day operation and maintenance of the water management system

surface water and groundwater monitoring

overall planning for the system

regulatory compliance of the system

review and update of water management models and documents.

6.4.7.2 Emergencies

After any emergency and response involving water management, any statutory reporting requirements will be completed in the first instance as necessary. An investigation will be conducted into the cause and the water management system and emergency and contingency planning reviewed to prevent a recurrence or ensure preparedness for any similar future situations.

Additional actions that may be taken in an emergency include:

controlling flow from structures if this can be achieved safely with immediate intervention (e.g.

contain flows utilising bunds and block flow paths as possible)

monitoring impacted water quality as soon as this can be done safely

notify stakeholders (e.g. Ports North, Maritime Safety Queensland, landowners, Traditional Owners)

and regulators as required

clean up spillage and repair or decommission structure following risk assessment.

6.4.7.3 Climatic Impacts

Regular site controls to manage drought will be based on:

regular and reliable monitoring of water storages and supply, and groundwater levels

accessible water monitoring records and databases

review of trends in water data and all relevant publically available data.

Regular site controls to support protection from high rainfall events will include:

management of freeboard in water containment and water storages prior and during the rainy

season (through diversion of pumped inflows where possible or exercise of authorised discharge,

releases, etc.)

separation of clean water from sediment laden water to limit volumes of sediment laden water

requiring management

maintenance of wet weather access and equipment

regular inspections of water management infrastructure

runoff assessment for site and infrastructure (and design and construction)


Page 6-31

inspections after significant rainfall events of water containment structures, water courses and

drainage lines for erosion and damage.

6.4.7.4 Controls to Prevent Failure

Regular site controls to prevent the failure of water retaining structures (e.g. sediment ponds) will include:

spillway construction with suitable capacity to prevent overtopping of embankments

inspection of structures prior to the rainy season and after any spillway discharge

management of water levels in water containment structures prior and during the rainy season

monitoring of dam embankments for structural stability.

6.4.7.5 Discharge Management

A discharge is defined as loss of water from an onsite water containment structure released to the environment; the discharge may or may not flow offsite. Regular site controls to prevent unplanned and unauthorised discharges will include the following:

Ensure that all sediment ponds have suitable outlet capacity designed to best practice standards to

prevent overtopping and embankment failure.

Inspect structures prior to the rainy season and after any spillway discharge.

Manage and monitor water levels in water containment structures prior and during the rainy season

including end of pipe authorised discharge.

Assess the likelihood of an overflows occurring based on rainfall information and site inspection.

Take additional actions in an emergency.

6.5 Water Balance

6.5.1 Water Demand

The estimation of the raw water demand for the Project from construction through to operation’s completion takes the following into consideration:

potable water supply for workforce during construction, ramp up and operations

allowance for vehicle wash-down requirement

dust suppression demand based on:

seasonal application rates for Port area and haul roads

scheduling of land clearing, timing of annual operations, etc. – factors that affect timing of dust

control requirements in these areas

allowance to maintain product water content

6.5.1.1 Potable Water

Estimates for the mine work force requirements are based on a unit demand of 300 L/person/day. Staff levels are reduced during the wet season.

6.5.1.2 Vehicle Washdown

An estimated wash-down demand of 17 m3/d has been allowed.


Page 6-32

6.5.1.3 Dust Suppression

Rainfall and evaporation data (refer Chapter 13) is considered to provide a reasonable basis for establishing local haul road dust suppression demand. Seasonal variations of the difference between rainfall and evaporation indicate that the highest annual demands for water application for dust control are most likely to occur from May through to November. Estimated water application rates (Figure 6-5) vary between 8.2 L/m2/d (October) and 2.3 L/m2/d (February). These rates are regarded as conservative (i.e. they would tend to overestimate the volume of water required for dust suppression).

Figure 6-5 Seasonal Water Application Rates for Dust Suppression

6.5.1.4 Product Moisture Content

To ensure sufficient dust control (dust extinction moisture) to the mined product, an allowance is made for addition of water at a transfer point before stockpiling at the Port Area. It is expected that losses will occur in transit in storage and handling between the mine areas, stockpile and barge loader. Estimates of water loss were supplied by the Project’s mining engineers. The annual requirement for dust suppression at the Port is estimated to be between 60 ML and 110 ML.

6.5.1.5 Construction and Maintenance

An allowance of 50 m3/d is included in the water balance calculation to provide for ongoing maintenance of site infrastructure. This is intended to provide a secure water supply for construction activities requiring compaction and concreting over the life of the Project.

6.5.2 Demand Summary

Potable water, vehicle washdown water and water for construction and maintenance may require higher water quality than water for dust suppression and product moisture content. Therefore water demand has been shown for two different water quality groupings in Figure 6-6 (high / medium water quality) and Figure 6-7 (low water quality). Low water quality demand is approximately 10 times the high / medium water quality demand.

Figure 6-6 and Figure 6-7 show construction (2016) through to Year 4 (2020) of mining, after which time water demand demonstrates the same monthly and seasonal variations over remaining years as Year 4. Maximum water demand reaches 1,653 m3 in the 2019 dry season and all dry seasons during mining


Page 6-33

thereafter. The maxima and average forecast demands (averaged monthly) are shown below in Table 6-3. There is considerable seasonal variability, particularly in the larger demands related to dust control on haul roads and in the product stockpile.

Figure 6-6 Water Demand (High / Medium Quality)

Figure 6-7 Water Demand (Low Quality)


Page 6-34

Table 6-3 Demand Summary

Category Maximum (m3/d)

Average (m3/d)

Potable water 35 29

Dust suppression 1177 718

Dust extinction moisture allowance 374 209

Construction & maintenance 50 38

Washdown - plant & equipment 17 13

Total 1653 1006

6.5.3 Water Supply

6.5.3.1 Water Supply Strategy

The following general principles underlie the water supply strategy, based on forecast demand and available sources:

The strategy must take advantage of all opportunities to recycle water within the operation.

The shallow aquifer resources in the Project area can provide reasonable volume and reliable yields,

and the groundwater is of good quality.

The shallow aquifer bores should be regarded as primary dry season supplies, and as such, should

only be accessed in the absence of alternative supplies to ensure that demands are met through the

entire dry season.

Surface water dams in addition to the kaolin mine water storage pits are not considered a feasible

source of water and hence are not considered any further.

Sediment ponds operating as a part of mining operations will collect surface runoff and potentially,

seepage inflows from shallow aquifers. These can be useful local storages through the wet season

and into the early dry season.

The primary water supply options are:

the kaolin mine water storage pits sources (Claystone Pit and Raw Water Pit, as shown in Chapter 5,

Figure 5-3

groundwater from shallow aquifers

There is an existing shallow aquifer borefield currently in use to meet demands such as the camp potable supply. Additional shallow aquifer bores will be constructed in the Namaleta Creek, Lunette Swamp and Port area borefields.

To ensure security of supply through the dry season, all surface water sources susceptible to evaporation such as the kaolin pits and sediment ponds, will be used in advance of the shallow aquifer sources.

Water supply from Great Artesian Basin (GAB) aquifer sources and / or from construction of additional surface water storage dams is not proposed for the Project.


Page 6-35

Due to inherent uncertainty in supply volume estimates considerable conservatism (i.e. lower than expected yields from water supply sources) has been built into the approaches adopted.

6.5.3.2 Kaolin Mine Water Storages

In order to estimate the potential yields of Claystone Pit and Raw Water Pit for use in supply, a preliminary assessment was carried out using a GoldSim model. The inflows to the pits include seepage from local alluvial groundwater, as well as surface runoff. Appendix 4 describes the modelling assumptions including dam catchment area, seepage rates, transmissivities, rainfall, evaporation, hydrological parameters and stage-storage-area relationships for the pits.

The analysis is considered to provide a reasonable basis for preliminary yield assessment. Data was provided by Gulf which states that the reliable continuous supply of the Claystone and Raw Water Pits was measured to be 25 kL/hour (600 m3/d) by previous operators of the kaolin mine. This is in line with the rate predicted in the Goldsim model, which gives an estimated reliability of 92% for a supply of 600 m3/d, as shown in Figure 6-8.

Figure 6-8 Estimated Yield of Kaolin Water Storages

6.5.3.3 Shallow Aquifers

The hydrogeology of the Project area, including shallow aquifers is described in Chapter 13. The shallow aquifers include groundwater to be sourced from the Bulimba Formation and from alluvial deposits adjacent to the creeks in the area. During previous kaolin mining operations, shallow bores that were used and that are available to the Project as supplies include bores in the Namaleta Creek and Lunette Swamp aquifer systems.

The Namaleta Creek borefield area has four bores (AKP02, AKP03, AKP04, AKP05), which are not currently in use and would require refurbishment for water supply. The Lunette system is host to the camp supply bore G1 (formerly AKP01). There are also production bores at the Port area, which are used intermittently at present (G5). These borefields and bores are shown in Figure 6-9.


Page 6-36

Six new shallow aquifer bores have been proposed to meet the water demand for the Project, with three bores proposed for the Port area, two in the Lunette aquifer and one in the Namaleta Creek aquifer north of Namaleta Creek), as shown in Figure 6-9.

The potential discharge rates for these bores have been based on previous studies for the kaolin mine (refer Chapter 13). Information provided by the previous mining lease holders to Gulf gives an estimate of the average yield of the shallow aquifer to be approximately 600 m3/d. This rate concurs with the results of yield testing carried out by Golders (1998) in the Namaleta Creek system, which resulted in recommendations for a borefield comprising four bores, each capable of delivering 155 m3/d. This would imply that discharge rates over the long term from each bore would be in the range of 1 to 2 L/s which is consistent with the sustainable discharge rates measured for shallow aquifer bores elsewhere in the Bulimba Formation in the Cape York area.

Local groundwater can be of sufficiently high quality as to not require even primary treatment. However, the bore water quality is subject to local conditions in the bore recharge capture zone where river and rainfall recharge the aquifer. Hence, any groundwater used in potable supply or to meet other higher quality water demand such as concrete batching will be tested regularly.

!(

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ML 6025

ML 40082ML 40069

SKARDON RIVER

NAMALETA CREEK

G1

G5(production)

Supply Lunette Bore

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Figure 6-9

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Existing and Proposed Boresfor Water Supply

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CAIRNS

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No warranty is given in relation to the data (including accuracy, reliability, completeness or suitability) and accept no liability (including without limitation, liability in negligence) for any loss, damage or costs (including consequential damage) relating to any use of or reliance upon the data. Data must not be used for direct marketing or be used in breach of privacy laws. Tenures © Geos Mining (2015). State Boundaries and Towns © Geoscience Australia (2006). Watercourses © Geoscience Australia. Imagery © ESRI (2015).

LegendMining Lease Boundaries

!( Port of Skardon RiverWatercourses

!>Existing and Proposed WaterSupply Bores

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NAMALETACREEK

SupplyBore #4

AKP02

AKP03AKP04

AKP05

1:30,000


Page 6-38

6.5.3.4 Sediment Ponds

Sediment ponds constructed as a part of normal operations can be used to provide a low quality water source for applications such as dust suppression and rehabilitation. However this has not been factored into the site water balance due to the unreliability of these sources for supply. Any use of this water will be opportunistic, and will further offset the need for use of shallow groundwater.

6.5.3.5 Great Artesian Basin and New Dams

Water supply from GAB aquifer sources and / or from construction of additional surface water storage dams is not proposed for the Project. Gulf recognises that a licence application to access GAB water was made in 2010. There have been a number of changes in legislation and policy regarding access to GAB water since 2010 and that licence application remains with DNRM. Gulf initially considered the GAB water would be required in conceptual mine planning for the Project in 2010 when beneficiation of the bauxite ore was proposed. The current mine plan does not propose beneficiation and hence GAB water is not required to supplement other sources.

Construction of a surface water dam has not been considered as it will have a high capital cost and impact on the local hydrology.

6.5.4 Supply Summary

Table 6-4 summarises the average sustainable yields of existing and proposed supply sources. The existing system (which would require refurbishment of the supply infrastructure) would supply an estimated 1,251 m3/d, which is not be capable of meeting the forecast demand at all times under the proposed regime of 9 months of mining annually. With the addition of new shallow aquifer bores, supply estimates increase to 1,741 m3/d.

Table 6-4 Existing Supply Sources

Source Source Comment Yield (m3/d)

Namaleta Borefield

Existing / Potential

Shallow aquifer; yield estimates from field testing by Golders (1998) for 4 bores at 130 m3/d each.

520

Lunette Borefield

Existing Camp supply bore (G1); estimate from field testing by Golders (1998) - 150 m3/d sustainable yield for each bore

150

Kaolin Pit surface storages

Existing Water Pit and Claystone Pit; yield estimated in current study for 95% reliability.

581

Sub-total – existing sources 1251

New Shallow Aquifer Bores

Proposed Comprising:

1 additional bore in Lunette shallow aquifer (150 m3/d)

4 additional bores in Bigfoot or Port area at ~85 m3/d per bore,

assumed average daily discharge of 1 L/s per bore. (Note that

there is an existing bore at the Port that may be suitable).

490

Total – all supply sources 1741


Page 6-39

6.5.5 Supply and Demand Forecasts

Figure 6-10 shows the water balance under the proposed supply options, which would require that additional bore capacity is installed prior to August 2017.

Figure 6-10 Water Balance Summary

The existing water supply is capable of producing 1,251 m3/d, however not all of this water supply is required on a daily basis, particularly in the wet season. Existing water supply sources will be used in preference to new supply sources. Over an annual period when the mine is at full production the estimated water supply from existing sources is 355 ML per annum, comprising 195 ML per annum from the kaolin pits and 160 ML per annum from existing shallow aquifer bores. Therefore, existing sources are capable of supplying more than is currently licensed.

Over an annual period when the mine is at full production the estimated water supply required from new sources (i.e. new shallow aquifer bores) is 35 ML per annum. These new sources are only required to meet peak demand during the dry season.

6.5.6 Demand and Supply Management

The water balance presented above represents a conservative scenario (i.e. higher demand than expected and lower supplies than potentially available). This provides a realistic, conservative scenario for the assessment of impacts to groundwater from shallow aquifer supply (refer Chapter 13). The following opportunities exist to reduce demand or increase supply, which are not considered in the water balance modelling:

Opportunistic use of water in sediment ponds will have some capacity to offset local demand.

Binding agents are proposed for use on roads to reduce the need for water for dust suppression.

Stabilisation of haul roads prior to mining is likely to include the application of a polymeric binding agent based on a calcium lignosulphonate compound that assists in reducing watering requirements for dust suppression during operations. Calcium lignosulphonate is a by-product of the pulp and paper industry.


Page 6-40

It reacts with negatively charged clay particles to agglomerate and stabilise the soil. A manufacturer has reported that trials have demonstrated water demand reductions of up to 90%. The median dust suppression demand over the Project life has been estimated to be 793 m3/d. A reduction in road-water usage of even 30% would result in a saving 238 m3/d which is equivalent to the yield of one to two shallow aquifer bores. In the absence of any proven site-specific information for the Project area, binder efficiency cannot be verified and therefore has not been taken into consideration in the Project water balance.

chapter 6 – water management - metro mining · chapter 6 – water management page 6-3 6.4 water...

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